'*.?*M Division of Agricultural Sciences UNIVERSITY OF CALIFORNIA SOYBEAN RESEARCH IN CALIFORNIA B. H. BEARD, P. F. KNOWLES (Editors) - ii filii t iiililiil^illllHl ^ CALIFORNIA AGRICULTURAL EXPERIMENT STATION BULLETIN 862 CAEBAD 862 1-70 (1973) Soybean yield and other data from small plot and field-size experiments in California have been included in annual reports of various research organizations for over 50 years. However, these data are not generally available to the public. Even though there has been no sustained commercial production of soybeans in California, there is a con- tinuing interest in the crop by farmers, oil mill processors, and consumer organizations. This bulletin summarizes the results of various soybean experiments in California and compares these results with data from other areas where the crop has been profitable to producers. JUNE, 1973 THE AUTHORS: G. H. Abel is Research Agronomist, Plant Science Research Division, Agricultural Re- search Service, USDA, stationed at University of Arizona Salt River Valley Experiment Station; B. H. Beard is Research Geneticist, Plant Science Research Division, Agricul- tural Research Service, USDA, stationed at University of California, Davis; E. C. Carlson is Specialist in Entomology, Department of Entomology, Davis; R. T. Edwards was Agronomy Extension Technologist, Agricultural Extension, Davis, at time this work was done; B. B. Fischer is Agriculturist, Agricultural Extension Service, Fresno; J. R. Goss is Professor and Chairman, Department of Agricultural Engineering, Davis; D. H. Hall is Extension Plant Pathologist, Department of Plant Pathology, Davis; W. A. Harvey is Extension Environmentalist, Division of Environmental Studies, Davis; D. W. Henderson is Professor, Department of Water Science and Engineering, Davis; P. F. Knowles is Professor and Chairman, Department of Agronomy and Range Science, Davis; A. J. MacKenzie is Soil Scientist, Soil and Water Conservation Research Di- vision, Agricultural Research Service, USDA, Imperial Valley Conservation Research Center; M. D. Miller is Extension Agronomist, Department of Agronomy and Range Science, Davis; R. J. Miller is Associate Water Scientist, Department of Water Science and Engineering, Davis; W. A. Williams is Professor, Department of Agronomy and Range Science, Davis. [2] CONTENTS Introduction 5 B. H. Beard, M. D. Miller, P. F. Knowles Morphology and development of the soybean plant 7 P. F. Knowles Economic facts: Supply, Competition, Use 10 M. D. Miller, B. H. Beard Climate factors 15 P. F. Knowles Soil factors 16 G. H. Abel, A. J. MacKenzie Management practices for various areas in California 18 B. H. Beard, P. F. Knowles Sowing methods and practices 20 P. F. Knowles, G. H. Abel, B. H. Beard Weed control 28 B. B. Fischer, W. A. Harvey Irrigation 34 D. W. Henderson, R. J. Miller Varietal testing and improvement 41 B. H. Beard, P. F. Knowles Spider mites and insects 44 E. C. Carlson Diseases 54 D. H. Hall Harvest and storage 56 J. R. Goss, M. D. Miller, R. T. Edwards Soybeans for forage and green manure 60 M. D. Miller, R. T. Edwards, W. A. Williams Summary and conclusions 63 B. H. Beard Acknowledgments 65 Literature cited 66 [3 WARNING University of California recommendations for pest control are based on the best information currently available. Treatments described in this bulletin are for information only and do not constitute a recom- mendation for use in commercial plantings. Treatments should give control without leaving residues that will exceed the tolerance estab- lished for any particular chemical. Because this crop is not commonly grown in California, tolerances have not been established. Before you treat for control, consult the latest U.C. Pest Control guide, your local Farm Advisor, or the local State Agricultural Commissioner for up-to-date recommendations. The grower is legally responsible for residues on his crops as well as for problems caused by drift from his property to other properties or crops. [4] SOYBEAN RESEARCH IN CALIFORNIA INTRODUCTION B. H. Beard, M. D. Miller, P. F. Knowles Because of its great usefulness, the soybean became one of the five sacred crops of China, along with rice, wheat, common millet, and glutinous millet. Soybeans were introduced to neighboring countries probably during the early years of the Christian period. It is very likely that soy- beans will provide an important part of the protein (as well as the vegetable oil) urgently needed to feed a rapidly expand- ing world population. The first published record of soybean trials in the U. S. was in 1804, and begin- ning in 1898 numerous introductions were made by the U.S. Department of Agricul- ture. The soybean industry of the United States is based on introductions from Man- churia, China, Korea, and Japan. At first soybeans were considered a hay crop, and even as late as 1940 the acreage grown for hay was equal to that for beans. Today, less than one-half million out of a total of 41.6 million acres are harvested for hay. The remainder of the crop is used as beans for production of oil, meal, and industrial products. The U. S. area of production increased dramatically beginning about 1954. Yield per acre has been maintained or even increased, so total production per acre has more than kept pace with the startling in- crease in acreage. In volume of production in the U. S., soybeans are about equiva- lent to wheat (both are far below corn). Of the present world production, about 75 per cent is in the United States and 20 per cent in mainland China. U.S. exports of soybeans have increased from 140 mil- lion bushels in 1959 to 410 million bushels in 1971. About one-half of U.S. exports go to western Europe and one-quarter to Japan. The early development of soybeans as a crop in the U.S. was centered in the Midwest, and most U.S. acreage is still in that area. However, southeastern states have increased their acreage greatly in recent years, primarily because of the de- velopment of better-adapted varieties, but partly because of the need for another crop and partly because of greater knowl- edge about the culture of soybeans in the South. For numerous reasons, soybeans have not become a volume commercial crop in the southwestern U.S. It is estimated that 600,000 tons of soy- beans or soybean products are used in California annually. Despite this large use (equal to 400,000 acres with a yield of 3,000 pounds per acre), California's agri- culture has had a disappointing role in the production of the crop. Soybean yield tests were started in Cali- fornia by the University of California as early as 1918, and in 1951 the U. S. Depart- ment of Agriculture and the University started research on soybeans at the South- western Irrigation Field Station in Braw- ley. This research, conducted principally in the Imperial Valley, was discontinued in 1963. The University also conducted extensive experiments throughout the San Joaquin and Sacramento Valleys in 1955, 1956, and 1957, and another soybean re- search program was started in 1966. The later was conducted cooperatively by the U. S. Department of Agriculture, Agricul- tural Research Service, Oilseed and In- dustrial Crops Research Branch, and the Departments of Agronomy and Range Sci- ence, Water Science and Engineering, Entomology, Agricultural Field Stations, and the Agricultural Extension Service of the University of California, Davis. A Submitted for publication May 25, 1972. [5] Soybean production, acreage, and exports, 1954-1971. grant to the University of California by the Oil Seed Crops Research Trust helped finance the 1966 to 1969 project. Almost 30 years of experience with soy- beans in California were summarized in 1944 by B. A. Madson (1944), who reported that yields under commercial production, though occasionally quite good, were not high enough to attract farmer interest on a sustained basis. Where yields were good, as on bottom lands of the lower Sacra- mento River and warmer coastal valleys, other crops would yield a greater net cash return per acre. He noted that the soybean varieties then available were susceptible to spider mites and to shattering. [6] The problems of today are largely the same as those enumerated by Professor Madson in 1944. Double cropping, germ plasm that is somewhat tolerant to spider mites, and varieties less susceptible to shattering are new developments in the last 10 to 15 years that allow some hope for future production of soybeans in Cali- fornia, but additional research is needed to develop adapted varieties. MORPHOLOGY AND DEVELOPMENT OF THE SOYBEAN PLANT P. F. Knowles The soybean (Glycine max [L] Merrill) a summer annual, was domesticated in north or central China from a closely related vine-like wild species G. ussuriensis Regel and Maack. It requires 75 to 175 days to mature, depending on the variety and the environment. Culture and harvest of the crop will be helped by an understanding of the development of the plant and seed. ROOTS. Soybeans develop a tap root penetrating to depths of 5 to 7 feet with most of the branch roots in the surface 2 feet of soil. Root development ceases at about the time seed development begins. Like other legumes, soybean roots de- velop nodules if the appropriate race or strain of RJiizobium bacteria is present. These nitrifying bacteria invade the plant through root hairs and form colonies, which appear as nodules. Each nodule con- tains millions of bacteria. The bacteria ob- tain carbodydrates from the plant, in re- turn supplying the plant with nitrates which they produce from the nitrogen of the air. (This cooperative arrangement is called 'symbiosis.') The strain of bacteria required by soybeans, being absent from California soil, must be added to the seed just before planting (page 25). STEMS. Stems are 1 to 6 feet tall, depend- ing on variety and planting date. They are usually erect, though some long-stemmed varieties lodge readily. With close spacing, branches are seldom produced. Usually branches rise at the base of the stem and do not rebranch. In soybean varieties from northern latitudes the terminal growing point elongates until the plant matures, and does not terminate with a cluster of flowers or pods. These are called inde- terminate types; such types continue vege- tative development and stem elongation after flowering commences. The determi- nate types (usually with a southern distri- bution) have stems terminating in a cluster of flowers or pods. Determinate types have more branches and are usually shorter (the Soybean plants terminating in a cluster of flowers or pods are called "determinate" types. [7] stems cease elongation after flowering com- mences) . LEAVES. The cotyledons (two halves of the seed) , following emergence from the soil, nourish the seedling for about 2 weeks from the beginning of germination. The first true leaves appearing above the cotyle- dons have single leaflets; thereafter, all leaves have three leaflets. At or before seed maturity the leaves drop off, their loss being hastened by fall frosts. Under California conditions, in the absence of fall frosts, leaves may remain longer than they do in the Great Plains, and may be a problem at harvest. FLOWERS. The flowers, small and incon- spicuous, are found mostly in axils of leaves. They are borne on racemes (clus- ters) of 3 to 15 flowers. Structurally they are similar to flowers of other legumes, such as peas or alfalfa. They are white, some shade of purple, or combinations of white and purple. The flowers, opening early in the morning, are self-pollinated. Soybean flowers are borne on clusters on the axils of leaves. Flowers appear first at lower nodes, usually 6 to 8 weeks after planting, and develop progressively upward as the stem elongates. About 75 per cent of the flowers abort without producing pods. Shedding is in- creased by low fertility levels, drought, and red spider injury. PODS. The pod generally has two to four seeds. The main colors are light straw- color, gray, or black, all of which may be modified in appearance by the color of the hairs on the surface. sgp% spf^i»^p if»a#!fHipeiWf ■ J Typical soybean specimens from five varieties grown in test plots. Pods have 2 to 4 seeds. Varieties are (left to right): Clarke, Lincoln, Hawkeye, Blackhawk, Brown Derby. [8] Table 1 COMPOSITION OF COMPONENT PARTS OF THE SOYBEAN SEED* Part of seed Proportion of seed Dry matter Nitrogenous substances Carbo- hydrates Fat Ash Entire seed Cotyledons Plumule Seed coat per cent 100 90 2 90.18 89.43 87.99 87.47 38.06 41.33 36.93 7.00 12.06 14.60 17.32 21.02 17.80 20.75 10.45 0.60 4.44 4.38 4.08 3.83 'From: The Soybean, by C. V. Piper and W. J. Morse. New York, N.Y.: McGraw-Hill Book Co. Inc., 1923. Used with permission of McGraw-Hill Book Company. Varieties differ greatly in tendency to shatter, a tendency increased by the dry atmospheres prevailing in California. As a consequence, many varieties with accept- able resistance to shattering in the Corn Belt suffer severe seed loss before harvest in California. PUBESCENCE. Most soybean varieties have a dense coat of hairs (pubescence) on the leaves, stems, and pods. Pubescence varies in degree and may be gray or brown in color. Smooth (glabrous) types have hairs only on the veins of the leaf. SEEDS. Seed development requires about 35 days after pollination. Dry-matter ac- TOTAL PLANT WEIGHT / BEANS \ - / P0DS\ - // STEMS \ \ S PETIOLES N. V LEAVES \ \ *i 1 1 1 1 1 ^>S| 60 80 100 120 DAYS AFTER EMERGENCE 140 Development of soybean plant. (Adapted from Hanway and Thompson.) cumulation varies from 60 to 90 pounds per day per acre. Commercial varieties grown for oil and protein have seed almost spherical in shape, ranging in size from 10 to 20 grams per 100 seed. Certain vege- table varieties, however, weigh up to 40 grams per 100 seed and are often flattened in shape. Some hay types may have flat- tened seed weighing less than 10 grams per 100 seed. The seeds of most commercial varieties are some shade of yellow, in some cases having a dark hilum (point of seed attachment). Seeds may also be green, black, brown, buff or combinations of these colors. Inside the seed coat are the two hemi- spherical cotyledons and between the cotyledons is the plumule (embryonic plant). Soybean seeds are easily injured by rough handling during harvest or in stor- age. Sometimes the injury is invisible (the cotyledons or plumule broken while the seed coat remains intact). Table 1 gives the chemical composition of soybean seeds. Most of the seed is made up of protein (nitrogenous substances) and oil, with twice as much protein as oil (Morse, 1950, and Piper and Morse, 1923). Seedling development. Soybean seeds ger- minate quickly, with the embryonic root (radicle) emerging first through the micro- pyle. The hypocotyl above the root and be- low the cotyledons grows rapidly. It is crooked in the middle, with the crook emerging through the ground first and pulling the cotyledons through behind it. Emergence occurs within 4 to 7 days under field conditions. After the cotyledons emerge tlfe hypocotyl no longer elongates, so the cotyledons remain close to the ground. [9] Plant development. The figure on page 9, which is based on data from Iowa, gives the pattern for development of a soybean plant. Note that development proceeds slowly in early stages but becomes very rapid about 50 days after emergence. ECONOMIC FACTS: SUPPLY, COMPETITION, USE M. D. Miller, B. H. Beard Farmers, oilseed processors, and oilseeds product users are all keenly interested in soybeans' potential for production in Cali- fornia for a number of reasons discussed below. Large quantities of soybeans and soy- bean products are imported and consumed in the state annually. For example, the California State Department of Agricul- ture in 1965 reported that the California feeding industry alone used 150,836 tons of soybean meal, a large proportion of the total usage of 993,312 tons of all types of protein supplement (Thomas and Braun, 1965) . Because of its high nutritional quality, soybean meal is expected to con- tinue to expand into this market. Total usage of soybeans for all purposes within the state is now estimated at 600,000 to 700,000 tons yearly. Freight costs of these and of commodities based on soybean oil and meal are estimated at in excess of $22 million. Alternatives or "new crops" such as soy- beans are not only desirable but urgently needed because of governmental crop acreage restrictions on cotton, rice, and the feed grains, and because of new land cur- rently coming under irrigation on the west side of the San Joaquin Valley. Although soybeans are a federally price-supported crop, to date there has been no economic need for soybean acreage-control programs. Existing California oilseed-processing fa- cilities, particularly in the San Joaquin Valley, have a capacity which could be used in slack or off-season periods to process soybeans. In recent years U. S. soybeans have been exported to Japan and other countries in great volume. For example, in 1970, 432.8 million bushels of soybeans were exported out of a total U. S. supply of 1,365.9 mil- lion bushels (USDA Economic Research Service 1971«). Soybean production in areas adjacent to such West Coast ports as San Francisco or Los Angeles should nor- mally have a transport cost advantage over soybeans produced east of the Rocky Mountains. Assuming an average yield of 3,000 pounds of soybeans per acre, 400,000 to 500,000 acres could potentially be devoted to the crop just to meet California needs, if local production costs can be competitive with the cost of imported domestic beans. Farm machinery generally available to California growers would be sufficient as specialized equipment is not needed for soybean production. Cost of producing soybeans in California Because soybeans have rarely been grown as a commercial crop in California, esti- mates of production costs are limited. Barnes and Burlingame (1967) reported 1966 Kern County cash materials and labor costs to be $82.75 per acre for a yield of 2,550 pounds of soybeans ($3.31 , per cwt) grown on a single-crop-per-season basis. Their report lists additional costs which prospective growers in other areas must consider (page 14). Amick and Allison (1968) reported the costs of growing soybeans in Georgia with * an average yield of 1,734 pounds per acre as a full-season crop, and a yield of 1,530 pounds per acre following cereals in a ,. two-crop rotation in a single year. These studies illustrate present cost-of-produc- tion advantages which other areas have in comparison with California. Total cash « and interest on operating capital costs of producing soybeans were $37.62 per acre ($2.17 per cwt) on a single-crop basis and $31.77 ($2.07 per cwt) as a second crop in the season. No land use or equipment depreciation charges were reported in the Georgia [10] studies. Comparison with the California study requires that appropriate additional charges be added. Assuming charges only one-third of those in California (total Cali- fornia depreciation and interest = $82.17 per acre), this would increase the Georgia costs by about $27.00 per acre, or to $3.72 per cwt and $2.95 per cwt, respectively. Compare these costs with the "All Costs at Varying Yields" column on page 14. The data clearly illustrate that California grow- ers who are considering soybeans as an alternative crop must face the fact that soybeans are already grown on over 42.8 million acres in states where irrigation is not required and land values and other production costs are currently appreciably below those in California. To be competi- tive, we must produce 3,000 to 4,000 pounds of beans per acre with present costs or find ways of growing soybeans at lower costs per acre. If soybeans are grown in California immediately following a winter cereal or vegetable crop, then the first crop could be assigned an appropriate proportion of the annual overhead costs, including taxes, thereby reducing the total cost of growing soybeans by from 15 to 25 per cent. Economics of double cropping In California, yields from experimental plots are similar for all seeding dates be- tween April 1 and July 1 (pages 21-23). , Consequently, there has been considerable interest in the possibility of including soy- beans in a double cropping system. Lack of moisture at seeding time is not a prob- lem in most of California because of irrigation. Economic relationships. Success or failure of double cropping with soybeans depends on timing of each operation and the rela- tionship of price of the beans, yield, and cost of production. Production costs de- termined for an individual farm can be more accurate than average costs. In areas where the land will be fallow during the summer unless used for soybeans, total costs for the year should be compared with p the total returns as well as the costs and returns for alternate land uses. There are two aspects of increasing the profit from a crop. Generally the price received, al- though variable, is beyond the control of individuals. Thus higher yields per acre and lower cost of production are the prin- cipal components subject to changes by the producer. Yields for many areas of California have been determined from experimental plots and are reported here. Although individual producers and farms will have varying yields, usually the best yields will be close to those determined experimentally for the area. The cost of production of soybeans can be varied by the individual producer. The methods of soil preparation before seeding can be varied as can be the number of cul- tivations and irrigations. (See "Manage- ment practices for various areas of Cali- fornia" page 18.) The lowest price for soybeans during the last 10 years was 3 \/ A cents per pound and the highest was 4i/£ cents per pound (USDA Agricultural Statistics 1970). These two extremes in price were used to con- struct the following graph, which shows the relationships between price, yields and production costs. This graph can be used in two ways. First, if average yields for an area are known they can be compared with the production costs for an individual producer to determine if soybeans are a profitable crop under his conditions. Second, if production costs are known the lowest profitable yield can be determined. Intersection points of any comparison fall- ing below the lower straight line will be a loss, above the upper straight line will be profitable, and between the two lines may be profitable, be a loss, or break even depending on the price at the time. 30 40 50 60 70 80 90 100 110 120 130 PRODUCTION COSTS (Dollars/Acre) Soybean yields, production costs, and price relationships. [ii] The long-term soybean outlook Information in this section is based upon recent published reports of the Economic Research Service, USDA, Washington, D.C. (1966, 1971a, 19716) and Foreign Agriculture Service, USDA, Washington, D.C. (1969, 1971a, 19716). As of October 1971, the primary production of world food supplies of several types including vegetable oil, had increased to the point where many nations which had been his- torically considered as importers were on an export basis. In appraising the long- term outlook for soybeans, one must consider the total worldwide oil-supply situation. Depending on supply and price, many vegetable oils can be used inter- changeably. Thus, one in excess supply tends to soften the price of competing substitute oils. World production of fats and oils in 1971 is projected to reach an estimated record 41 million metric tons (fat or oil equivalent), about 10 per cent above the 1963-67 average (USDA Foreign Agriculture Service 19716). This estimate includes edible and industrial vegetable oils produced largely from oilseed crops, palm, animal, and marine oils and fats. Unlike food grains, however, per capita increase in world production of edible fats and oils has not been striking. World- wide, edible fats and oils output increased about 35 per cent from 1957 to 1968 while populations advanced 25 per cent (world production per person rose from under 18 pounds to 19 1/9 pounds). The big in- crease in edible vegetable-oil production occurred in the developed countries, which accounts for about 60 per cent of total world production of edible fats and oils. World per capita consumption of food fats and oil is generally low compared with that in the U. S., where each person con- sumes about 50 pounds annually. There is opportunity for future export expansion of vegetable oil to the developing coun- tries if the problem of low consumer buy- ing power can be solved (USDA Economic Research Service 19716). U. S. position. All through the 196()'s the U. S. has produced about one-fourth of world supply of oilseeds, fats, and oils, and provided one-third of world exports. This large vegetable-oil export program has been anchored to the rapidly expand- ing U. S. soybean production, where three- fourths of the world total was grown in 1969 (USDA Foreign Agriculture Service, 1969). Because about 25 to 32 per cent of the annual U. S. soybean crop is exported, short-term changes in world supply can exert considerable effects on the U. S. competitive position and unsupported farm prices for soybeans in any one year. The data on page 14 show soybean production and use in the U. S. since 1959 (USDA Economic Research Service 197 la). The principal soybean-producing states include those in the corn and cotton belts, with the principal area of soybean production being the North Central states, the Mississippi delta, and the Middle At- lantic coast. Soybean utilization The soybean, long known as "the meat of the fields" in the Orient, has come to be known as "The Marvel Crop" in U. S. agriculture. Although about a century has passed since the crop was first introduced into the U. S. it was the modern chemurgic era that skyrocketed the crop into prime commercial importance. The crop's ver- satility accounts for the many uses to which it is put. For forage. Soybeans are used for the pro- duction of hay. For hay of best quality, plants are cut when the seeds in the pods are about half developed. They are also grown in combination with other crops for pasturage and silage. For human food. Production of soybean oil now far exceeds in volume and value that of any other edible vegetable oil. The oil is used in making margarine, shorten- ing, salad oil, and other food products. Recent advances in food technology have created a high-volume market for proc- essed soybean meal for human food, al- though it is still only a small percentage of the total usage. Soybean meal is used to make high-protein soy flour, which is used in diverse forms in breakfast cereals, breads, cakes, cookies, crackers, and fill- ings. Soy flour and grits (coarser particles) are used in pancake mixes, cake mixes, macaroni, dry foods, and packaged and canned food. Soybean meal products re- [12] SOYBEANS: ACREAGE, YIELD, AND PRODUCTION IN VARIOUS COUNTRIES, AVERAGE 1962-1966, ANNUAL 1968-1970* Acreage t Yield Per Average acre Production Continent and Average Average Country 1962-66 1969 1962-66 1969 1962-66 1969 1,000 1.000 1,000 1,000 acres acres Bushels Bushels bushels bushels North America : Canada 245 322 29.1 23.8 7,126 7,664 United States! 31,602 40,857 24.3 27.3 768,672 1,116,876 Mexico 56 395 30.8 25.3 1,721 9,994 South America : Argentina 36 70 16.1 16.7 582 1,168 Brazil 957 2,297 16.1 15.2 15,367 34,906 Colombia 61 138 23.2 26.8 1,429 3,711 Paraguay § 18 69 20.7 15.9 370 1,102 Europe : Romania 22 133 10.2 14.1 228 1,870 Yugoslavia 16 11 20.2 18.8 330 201 U.S.S.R. 2,106 2,125 7.6 9.3 16,049 19,105 Africa : Nigeria || • ■ ■ 673 300 Rhodesia§ H 2 6.5 11 10 Tanzania** 10 12.1 125 South Africa § If Asia: Iranft 22 33 5.2 7.9 113 257 1 . . 8.9 . 10 121 Turkey 14 20 12.5 16.7 178 331 China : Mainland 19,915 19,770 13.0 11.5 259,600 230,000 Taiwan 130 112 16.4 22.0 2,148 2,466 Cambodia 29 25 10.8 13.4 312 331 Indonesia 1,433 1,221 10.1 12.5 14,442 15,297 Japan 528 254 18.4 19.7 9,718 4,986 Korea, South 709 761 8.4 11.1 5,959 8,416 Philippines 5 4 12.7 12.3 59 44 Thailand § 77 51 14.4 21.4 1,112 1,102 Other countries 1,099 1,105 8.1 9.5 8,949 10,480 Total excluding Romania, U.S.S.R., Bulgaria, Hungary, Mainland China, North Korea, and North Vietnam§§ 36,164 46,897 22.9 25.8 829,120 1,210,088 Estimated world total§§ 59,229 69,944 18.8 21.0 1,113,273 1,470,868 * Years shown refer to years of harvest. Southern Hemisphere crops harvested in the early part of the year are combined with Northern Hemisphere crops harvested in the latter part of the same year. t Harvested area as far as possible. t Acreage harvested for beans. § Planted area. || Quantities purchased by the Nigerian Marketing Boards for export. 11 European farms only. ** Sales. tt Less than 5 years. §§ Includes estimates for the above countries for which data are not available and for minor producing countries. Data from USDA, Foreign Agricultural Research Service reports. [13] SAMPLE COSTS OF PRODUCING SOYBEANS IN KEEN COUNTY, 1966^ lours per acre Cash and Labor Cost Per Acre I Operation Labor 'Fuel and repairs — equipment Material and other costs Total sample costs Cultural : Land preparation 2.5 $3.50 $2.75 $ 6.25 Plant .5 .70 .55 Seed: 70 lbs. @ \1$ $ 8.40 9.65 Irrigate: 1 pre-6 crop 8.0 9.60 2.50 Water : 3 ft . @ 6.00 18.00 30.10 Cultivate : 3 times 1.5 2.10 1.65 3.75 Taxes 12.50 12.50 Miscellaneous overhead 2.60 2.75 4.65 10.00 Total cultural costs $18.50 $10.20 $43.55 $72.25 Harvest : Combine $ 8.00 Haul 2.50 Total harvest costs $10.50 Total cash and labo r costs $82.75 All Costs at Varying Yields Investment Per acre Annual Cost Depreciation Interest Pounds Cost Land $900.00 $54.00 per acre per cwt. 1,500 $10.99 2,000 5.25 2,500 6.60 Irrigation facilities Tractor 5 Vz hrs. Equipment Total 200.00 20.00 $15.00 3.30 2.00 6.00 1.27 .60 3,000 5.50 3,500 4.71 $20.30 $61.87 $82.17 4,000 4.12 4,500 3.66 Total cost ; per acre $164.92 Data prepared by Roy M. Barnes and Burt B. Burlingame SOYBEANS: SUPPLY DISPOSITION, ACEEAGE AND PRICE IN THE U.S., 1959-72 Item Year Beginning September 1959 1965 1970 1972' Item Year Beginning September 1959 1965 1970 1972' Acreage planted Acreage harvested 23.3 Acreage and yield (million acres) 35.2 43.3 46.4 Supply fc >upply and Disposition (million bushels) for beans Per cent harvested 22.6 97.0 34.4 42.0 97.7 97.0 45.8 98.7 Beginning Stocks, Sept. 1 Production 87.8 532.9 29.7 845.6 230.1 1,123.7 71.9 1,351 Yield per acre harvested 23.5 (bushels) 24.5 26.8 29.5 Total supply 620.7 875.3 1,353.8 1,423 Price per bushel Price (dollars) Disposition Support (U.S. Crushings 394.0 537.5 760.1 765 farm basis) 1.85 2.25 2.25 2.25 Exports 139.9 250.6 433.8 510 Received by Seed 29.3 42.9 48.3 ) farmers 1.96 2.54 2.84 3.201 Feed 1.5 .9 1.0 )73 No. 1 yellow, Residual 4.2 7.8 11.7 ) 111. pts. 2.07 2.91 3.00 — Total No. 1 yellow, disposition 568.9 839.7 35.5 1,254.9 98.9 1,348 75.0 Chicago 2.17 2.98 3.05 — Ending stocks, Aug. 31 51.8 * September indications. t Forecast. Data from USDA Economic Research reports. Service 14] cently developed are used as a wholesome, nutritious binder for making sausage and meat loaves and for whipping agents. They are also being used to produce high- quality meat-like and milk-like products. Protein for livestock feeding. Soybean meal is the first ranking vegetable protein livestock feed supplement in the U. S. and 90 per cent of the meal produced is utilized in this manner. Every pound of soy oil produced leaves 4 pounds of high- protein meal. It has proved an excellent protein feed for livestock and poultry. Industrial uses. New chemical knowledge has proven soybeans to be an excellent source of structural and decorative ma- terials for homes, offices, and factories. Soybean meal is used in making a series of protein products which, in turn, are made into low-cost adhesives. These pow- erful adhesives are used for many purposes, including plywood. Other uses include wallpaper, coated printing papers, and ad- hesive tape. They are used in the manu- facture of the new cold-water paints. Soybean oil is used to make paints, varnishes, enamels, and lacquers. Lino- leum, putty, caulking compounds, leather dressings, lubricating greases, and water- proofing coatings are all now being pro- cessed from soybean-oil formulations. CLIMATE FACTORS P. F. Knowles The soybean is a warm-season crop which requires the same general climate as corn, and this probably explains why it has been so successful in the Corn Belt. Day length and humidity are very important factors in soybean production. Day length. All varieties will flower 20 to 28 days after emergence if there are 12 hours of daylight or less; in other words, it is a short-day plant. When day lengths are over 12 hours, varieties differ in flower- ing response. Varieties with the shortest day requirements are found in semi-tropi- cal and tropical areas; under long days these varieties grow vegetatively, either failing to flower or flowering only late in the growing season, as days shorten. Long- day varieties, which are adapted to north- ern latitudes in the northern hemisphere, flower very early under short-day condi- tions (page 41). The flowering response of soybeans to different day lengths is determined by a pigment named "phytochrome" which is a soluble protein that is very unstable once it is extracted from the plant (it has a half-life of 20 minutes at room tempera- tures). Phytochrome exists in two photo- reversible forms: P r , with absorption in the red portion of the light spectrum (wavelengths of 590 to 680 m/i); and P fr> with absorption in the far-red portion (wavelengths of 700 to 800 m/i). Irradia- tion of the plant with light of 590 to 680 m/i shifts the pigment to P fr , the active form of phytochrome that stimulates flower development. P jr reverts to P r , the inac- tive form, quickly in sunlight (450 to 700 m/i) and slowly in darkness. The degree of reversal is less with long nights (short days); hence, flowering response is stimu- lated by short days. Humidity. Soybeans require a moist warm climate, and have been economically un- successful in areas with prolonged periods of low relative humidity. Prolonged low humidity seems to aggravate two prob- lems: shattering and spider mites. Many varieties developed for the humid areas of the Corn Belt tend to shatter excessively as they approach maturity in a dry climate, although recently developed varieties are partially resistant to shattering. Even with less shattering, spider mites are a serious problem under dry, dusty conditions. Mites arc a problem in the soybean pro- duction areas of the U. S. only after ab- normally long periods of drought, but they are generally prevalent throughout Cali- fornia. Temperature. Soil temperatures at seed- ing depths should average 65° F before [15] planting; at lower temperatures emergence will be delayed and some seedlings will not survive. Temperatures above 100° F slow soy- bean growth. When plants are flowering, hot dry winds seriously reduce seed setting. Seedlings and fully developed plants are not injured by light frosts. SOIL FACTORS G. H.Abel, A. J. MacKenzie Soil types. Soil types favorable for the growth of other crops are suitable for soy- beans. Ideal for optimum growth are deep, friable soils with good drainage and aera- tion characteristics; also desirable are medium-textured soils with a high water- intake and water-holding capacity. Avoid saline soils containing soluble salts above 5 to 7 millimhos per cm (mmhos per cm) electrical conductivity of saturation paste extract. Effect of salinity. Salinity decreases avail- ability of soil water to plants. The salts responsible for salinity are mainly cations of sodium, calcium, and magnesium, and anions of chloride and sulfate (table 2). These salts increase the osmotic pressure of the soil solution in direct proportion to the salt concentration. Salt concentration increases rapidly as soil moisture is de- pleted. Saline soils require irrigation more often than nonsaline soils because the range of available moisture is less. Toxicity to the chloride ion is quite apparent in many of the varieties de- veloped for highly leached soils east of the Rocky Mountains. Seed germination and seedling to maturity are two separate growth stages that may show high, inter- mediate, and low tolerance to excessive chloride in the soil. Chloride tolerance for the two stages of growth are unrelated, and all combinations have been found in different varieties of soybeans. For ex- ample, the Lee variety has low chloride tolerance during germination but high chloride tolerance during later growth, whereas the Jackson variety has the re- verse. Other varieties may have either high or low chloride tolerance during both stages of growth. For further details see Abel and MacKenzie (1964). During seed germination, rate and per cent emergence of all soybean varieties are decreased when the salt concentration of the soil saturation paste extract is above 7 mmhos per cm. Salt-susceptible varieties are more affected than the toler- ant. At lower salinities all varieties reach ultimate emergence, although the tolerant do so in 1 week and the susceptible in 3 weeks. During the growth stage, toxicity in the chloride-susceptible varieties appears as an incipient light-brown necrosis be- ginning at the leaf tips, advancing to the leaf margin, and then moving inward un- til the whole leaf is affected. The entire plant can become affected, with death ensuing. In direct contrast are the chlor- ide-tolerant varieties, which do not show necrosis to salinities up to 10 mmhos per cm. Above this level, the plant tissues die from physiological drouth and root de- terioration. Table 2 CHEMICAL COMPOSITION OF SATURATION-PASTE EXTRACTS OF THREE SALINE SOILS IN THE IMPERIAL VALLEY Soil Electrical conductivity Soluble cations Ca~ Mg" Na+ K+ Soluble anions HCO; so; CI mmhos. per cm. meq. per liter Imperial silty clay 6.8 30.5 19.6 38.0 1.7 6.5 58.3 26.1 Meioland loam 7.0 32.4 19.7 32.0 0.6 3.8 52.6 29.5 Holtville silty clay 5.0 24.2 12.0 30.0 1.0 7.5 48.4 17.0 [16] Uptake of chloride in stems and leaves is high in chloride-susceptible varieties, but tolerant varieties are able to exclude virtually all the chlorides. As an example, 1-month-old plants of the susceptible variety Jackson and the tolerant variety Lee contained 30,000 ppm and 140 ppm chloride in the stems respectively, and 50,000 ppm and 100 ppm chloride in the leaves, respectively. Seed yield of the chloride-susceptible varieties is reduced when soil salinities are 5 mmhos per cm or higher, whereas the chloride-tolerant varieties show no reduc- tion in yield until salinities exceed 9 mmhos per cm. Chloride- tolerant soybeans should thrive well in salinities of 8 mmhos per cm if emergence is good and there are no other limitations on growth. A salinity of 8 mmhos per cm reduces height even with resistant varieties, and there is a harvest problem when a portion of the podding is too close to the soil surface for combine harvest. The usual recommenda- tion is to select fields with salinities no higher than 5 or 6 mmhos per cm, be- cause higher salinities indicate other seri- ous problems which would limit soybean growth. The leaves of susceptible varieties are a paler green when grown in a substrate with moderate to high concentrations of salt, but leaves of tolerant varieties re- main normal green under similar con- ditions. Effect of boron. Soybeans have a low requirement for boron, with 0.1 ppm available boron content of soils required for optimum growth (Berger, 1949). Boron toxicity effects have been observed in the Central Valley of California. Boron in ex- cess of 0.5 ppm causes a speckled type of necrosis, which may lead to plant death. Excessive boron reduces plant metabolism and seed yield. Nutrient uptake and fertilizer needs. Soy- beans grown in the Imperial Valley have produced 4.3 tons of dry matter per acre (oven-dried at 70°C). This included 3.0 tons of vegetative material (stems, leaves, and petioles) and 1.3 tons of fruiting ma- terial (pods and beans). Iowa-grown soy- beans have been reported to produce 3.2 tons of dry matter per acre, 2.1 and 1.1 tons of vegetative and fruiting portions, respectively (Hanway and Thompson, 1967). Nitrogen content of soybeans, obtained through nitrogen fixation and uptake from the soil, is approximately 250 pounds per acre. The harvested seed contains 110 pounds of nitrogen, leaving 140 pounds per acre to be returned to the soil with plant residue. Phosphorus and potassium uptake by soybeans has been reported to be respec- tively 17 and 77 pounds per acre. Har- vested seed per acre contains 12 pounds of phosphorus and 40 pounds of potas- sium (Hanway and Thompson, 1967). Soybean plants require other nutrients, such as calcium, magnesium, sulfur, iron, manganese, molybdenum, zinc, and cop- per. Unlike nitrogen, phosphorus, and potassium these nutrients are not com- monly deficient in soils. Although the very early stages of growth require only relatively small amounts of nutrients, early plant growth is promoted by high concentrations of nutrients in the root zone at that time. If needed, fertiliz- ers can be applied preplant by broadcast spreading and discing before bed prepa- ration, but preferable application is in a band 1 to 2 inches to the side and slightly below the seed. Placing the fer- tilizer too near the seed or with the seed can result in salt injury to the plant. In the Midwest, top soybean yields are gen- erally obtained on fields with high potas- sium and potash levels built up by a con- tinuous program of high fertilization. Nitrogen. Nodulated soybeans generally do not respond to nitrogen fertilizer as do nonlegume crops. When properly nod- ulated, soybean roots may derive a con- siderable portion of the nitrogen needs of the plant from nodules through the fixation of atmospheric nitrogen. Appli- cations of nitrogen tend to retard the nodulation of seed-inoculated soybeans planted in rhizobia-free soil. Applications of 100 pounds of nitrogen at planting time in the Imperial Valley, where rhizo- bia were not present in the soil, resulted in poorly nodulated soybeans and yields of only 360 to 960 pounds of beans per acre. Omitting nitrogen at planting time permitted good nodulation and yields of [17] 2100 to 2400 pounds of beans per acre (Carter and Hartwig, 1963). Initially the soybean seedling is ex- clusively dependent on the soil and coty- ledons for nitrogen and must wait for the development of nodules for symbiotic nitrogen supplies (Ohlrogge, 1963). Seed- ling soybean leaves will show nitrogen- deficiency symptoms when grown in nitro- gen-deficient soil, but with proper inocu- lation nitrogen fixation initiates normal growth 4 or 5 weeks after emergence. Studies in the Imperial Valley have shown no growth responses to different levels of nitrogen fertilizer applied to nitrogen- deficient soil at preplant and bloom stages. Phosphorus. The roots absorb phosphorus and translocate it to the plant parts in different amounts. The leaves and plant top contain about twice as much as the stems. During plant maturation, about 75 per cent of the phosphrous moves into the seed. In the South, phosphorus applied as a fertilizer will induce a response in soy- beans when the soil contains less than 40 pounds per acre of this nutrient. No re- sponse to phosphorus has been obtained in the Imperial Valley, probably because the soil contained the minimal amounts needed for optimum plant growth. There- fore, when soil phosphorus is less than the minimal, apply approximately 50 pounds of P 2 O s per acre for the soybean crop. Additional phosphate fertilizer would be reserves for succeeding crops. Potassium. This highly mobile constituent in the plant is particularly abundant in young tissues. The soil is well supplied with potassium, and it should never be exhausted where irrigation water is ap- plied from watersheds which provide dis- solved potassium salts. Magnesium and sulfur. If deficient, mag- nesium and sulfur should be incorporated in soil as fertilizer supplements. Mag- nesium is highly mobile in the plant and is used mainly in forming the chlorophyll molecule and in certain enzymatic reac- tions. Sulfur promotes root nodulation in addition to other plant functions. None of the other essential elements has been found deficient. If and when they do become deficient they should be added to the soil for optimum growth. MANAGEMENT PRACTICES FOR VARIOUS AREAS IN CALIFORNIA B. H. Beard, P. F. Knowles If soybeans are to become a successful crop in California, they will not only have to be profitable but be more profitable than other crops that could be grown at the same time at comparable risks. Al- though soybeans can be grown as hay, silage, or green manure crops the primary market is for the beans. At present yield levels (2000 to 3000 pounds per acre) it appears that double-cropping offers the best possibility for soybeans to succeed as a profitable crop in California. Soybeans will fit into most cropping systems used by California farmers grow- ing grain crops. All cultural operations can be handled by row-crop equipment used for seeding and cultivating cotton or corn with only minor adjustments. A properly adjusted grain combine can be used for harvest. Because the soybean is a legume, it does not deplete the soil of nitrogen. In soybean areas the crop has been observed to have a beneficial effect on soil structure. It produces minimum residue quickly and easily incorporated into the soil during preparations for seed- ing the following crop. In major soybean production areas of the U. S. it is generally a full-season crop, occupying the land from May through October. In the South, and in southern portions of the Corn Belt, a small per- centage of the total soybeans are also grown as the second crop in a 2-crop 1- [18] year rotation along with small grains. Lack of moisture at seeding time has been the major hazard to that practice in those areas. Although yields from experimental plots in California tend to be higher from earlier seeding dates, yields are not greatly reduced by planting as late as July 1; as a consequence there has been consider- able interest in the possibility of includ- ing soybeans in a double-cropping system. Lack of moisture at seeding time need not be a problem in California if crop irrigations can be given when needed. Imperial Valley. Soybeans have been grown here in experimental plots follow- ing early-harvested sugar beets and fol- lowing barley. The minimum tillage needed following sugar beets caused no special problems. The beds were thrown up with furrowing shovels, and soybeans were sown on top of the ridges. Following barley, the field should be disced and irrigated. After 2 or 3 weeks the soil is dry enough to make beds and plant the soybeans. An irrigation must follow within 2 days after sowing. Irri- gations cause weed seeds and volunteer barley to germinate, but the weeds can be controlled with herbicides if it is nec- essary and the barley will die or be stunted by hot weather during July and August. This system requires attention to details and careful control of the timing of the various operations. If the barley can be harvested during the middle to later part of May, and the initial discing and pre- irrigation completed around June 1, there will be adequate time to seed the soy- beans before July 1. Southern San Joaquin Valley. In the southern San Joaquin Valley a 1-year crop- ping system of potatoes and soybeans ap- pears practical. Following potato harvest, the soil is generally loose and requires re- shaping of beds before soybeans are sown. Experimental soybean plots following po- tatoes on land of the Kern County Land Company near Wasco have shown that careful water management is required to obtain good stands. Growing soybeans as green manure between potato crops seems to help control potato scab due to Strep- omyces scabies. It is not known if harvest- ing a crop of soybeans between potato crops would have the same effect. Soybeans and barley have not been tested but ap- pear possible in a double-cropping system in the area. Central San Joaquin Valley. Extensive double-cropping experiments have been carried out at the West Side Field Station, using barley and soybeans. Barley is broad- cast on a level seed bed, and beds are thrown up with furrowing shovels. A single heavy irrigation will usually germi- nate the barley seed and produce good stands. After the barley harvest the soy- beans are seeded into the top of the beds and immediately irrigated to germinate the seed. Care must be taken to thor- oughly wet the bed to the location of the seeds. Double-cropping minimum-tillage ex- periments were conducted in 1968 and 1969 in conjunction with herbicide tests described in another section of this re- port (only the tillage effects are discussed here). Three levels of pre-sowing tillage were used: no tillage; a sectioned rolling cultivator, and a power-driven rotary culti- vator. These respectively represented none, medium, and thorough tillage. The barley straw was burned on half of each Table 3 YIELD DATA FROM DOUBLE-CROPPING EXPERIMENTS WITH SOYBEANS AT THE WEST SIDE FIELD STATION, FIVE POINTS, 1968 AND 1969 Preplant tillage Burned Nonburned Two-year average 1968 1969 Average 1968 1969 Average None 1505 1490 1460 1380 1338 1396 1443 1414 1428 lb. per acre 1375 1577 1600 1388 1284 1416 1382 1431 1508 1412 1422 1468 Thorough 1485 1372 1429 1517 1362 1440 1434 [19] Table 4 YIELD DATA FROM TESTS OF SOYBEAN VARIETIES AND SELECTIONS GROWN ON SUMMER FALLOW AND AFTER BARLEY CUT FOR HAY, DAVIS, 1957 Maturity group Number of entries Summer fallow After barley I II 6 8 15 lb. per acre 2137 1773 1764 2225 1995 1580 Average - 1891 1933 replication, and was shredded with a flail- type cotton-stalk chopper on the other half. A starter application of nitrogen fer- tilizer (25 pound N per acre) was chiseled about 5 inches deep into the beds. Inocu- lated seed was sown into the dry beds in June and the test area was irrigated im- mediately. A 5-foot by 43.5-foot (0.005 of an acre) strip was combined from each plot. Table 3 shows yields for each experi- ment. The varieties Wayne and Kent were used, respectively during 1968 and 1969. Tillage differences were not associated with significant yield differences, and yields did not differ significantly whether the straw was burned or shredded. Burning the straw is wasteful of organic matter and contributes to atmospheric pollution. From a cost standpoint, the no-tillage plots were obviously more economical. The big- gest problem is keeping the inoculum alive in the hot, dry soil until the post-seeding irrigation water reaches the seed. With the proper varieties of soybeans, harvest can be in October or the first part of November. Thus the following rota- tional crop can be sown in November or December. Seed size and quality, as well as oil content and meal percentage, were not affected by the tillage or straw treatments. In a similar experiment, yield was not affected by increased amounts over 25 pounds of nitrogen per acre. Southern Sacramento Valley. In 1957, variety tests were sown on both summer- fallow land and on stubble land after a crop of barley cut for forage in early June. After the barley stubble was disced down the entire test area was furrowed and irri gated prior to planting. A level seedbed was then prepared by discing and harrow- ing. Plantings were made in rows 30 inches apart on June 20. Plots were single rows, 20 feet long, with 16 feet of row cut for yield determinations. All seed was inoculated. Yields for any maturity group were essentially the same whether sown on summer fallow or sown after barley (table 4). SOWING METHODS AND PRACTICES P. F. Knowles, G. H. Abel, B. H. Beard Sowing is a critical operation in growing soybeans because often crop failures can be traced back to errors in choice of seed, rate of depth of seeding, choice of wrong type of inoculum, and so on. Choice of variety is so important to economic suc- cess that it is discussed in a separate section (pages 41-43) . Seedbed preparation. Seedbed prepara- tion varies from one area to another of California, but will be about the same as that used for other irrigation row crops in the district. (See pages 18-20 for seed- bed preparation details for soybeans as the second crop.) Good stands have frequently been ob- tained with flat plantings, provided the seedbed is level and moisture is main- tained close to the surface of the soil. Flat plantings are used in the Midwest and in [20] the South. One disadvantage of flat plant- ings in California becomes apparent at harvest. When furrows are prepared for irrigations, soil is thrown to the base of the plants, in effect producing a raised bed. Raising the bed after plant establish- ment will decrease the distance between the soil surface and the lowest pods, thereby increasing bean losses during harvest. Success is best achieved with sowings made on top of raised beds. To facilitate combine harvesting, beds should be thor- oughly settled, uniform in height and shape, not too high, and free from clods. They should be firm, with moisture near the surface of the soil. Quality of seed. It is important to use high-quality unbroken seed having at least 85 per cent germination. Use a ger- mination test to determine the number of seed that will germinate and produce strong seedlings. The viability of undam- aged seed is short-lived; 1 year of non- airconditioned shed storage reduces the germination level considerably. Where possible, certified seed grown the previous season should be used. Until soybeans are regularly grown in California, arrange- ments for seed purchase will be necessary well in advance of the seeding date. Date of seeding. Optimum seeding dates are not greatly different for most areas of California. For economic reasons it is generally advisable to plant soybeans as the second crop in a double-cropping sys- tem after a cereal or vegetable crop. Other advantages of later dates of seeding are: (1) the growing season is shorter, with less water required and less weed control; (2) flowering occurs when days are shorter, after the high temperatures of mid-sum- mer; and (3) pods mature in the fall, when relative humidities are higher and shat- tering is less. In the Imperial Valley the highest yields for Lee (Maturity Group VI), an adapted variety, were obtained from plantings made between mid-May and mid-June (table 5 — maturity group classifications are explained on page 41). With this range of planting dates, maturity varied over a period of one week and height was about the same. Plantings after July 1 were dis- tinctly and progressively shorter in height and lower in yield. If an adapted short-day variety, such as Lee, is planted in February and March in the Imperial Valley, the plant will begin to flower very soon after stem elongation begins because the days are short. Because of the longer days in May and June the plant enters a vegetative phase and stops flowering. It will begin flowering again later in the season, but the total yield will be low, and the seed quality poor. Lodging may result from the excessive vegetative growth caused by the long growth period (Abel, 1961). Yields of the variety Clark (Group IV), sown in a test at the U.S. Cotton Research Station at Shafter, were above 3000 pounds per acre when sown on June 1 1 and June 25 (table 6). In a seeding on July 16 the yield had dropped about one-third. The seeding of June 25 gave less lodging and shorter plants than that of June 11. Oil content decreased with later dates of seeding. Table 5 AVERAGE PERFORMANCE OF SOYBEAN VARIETY LEE (MATURITY GROUP VI) AT THE USDA SOUTHWESTERN IRRIGATION FIELD STATION, BRAWLEY, 1957 Date of planting Planting to flowering Flowering to maturity Date ripe Plant height Seed quality score" Yield May 2 May 15 May 29 June 18 July 3 July 15 Aug. 2 dc 81 75 69 59 55 46 40 ys 101 92 85 82 74 72 75 10/31 10/29 10/30 11/6 11/9 11/10 11/25 in. 30 31 35 31 18 16 7 2.7 2.3 2.7 1.8 1.3 1.0 1.0 lb. per acre 1842 2598 2394 2532 1506 1824 648 *1 = excellent, 5 — poor. [21] Table 6 AVERAGE PERFORMANCE OF SOYBEAN VARIETY CLARK (GROUP IV) AT THE U.S. COTTON RESEARCH STATION, SHAFTER, 1957 Date sown Date mature Height Yield Oil* Protein" Oct. 25 Nov. 4 Nov. 26 in. 52 49 44 lb. per acre 3065 3175 1930 20.0 18.6 17.8 per cent 37.1 June 25 July 16 35.8 36.7 "Basis 10% moist jre. At the West Side Field Station in 1966 and 1967 yields decreased progressively from mid-May to mid-June planting dates (tables 7 and 8). Boron injury was ob- served in these tests, and the low yields may have been a result of this injury. Mite damage has usually been severe and in 1967 the difference between the yields of the May 15 and June 6 planting may have been due to greater insect injury with the latter date of planting. At Davis in 1955, Group O varieties did not differ appreciably in yield between plantings on May 16 and July 2 (table 9). But with Groups I and II there was a greater difference in favor of the earlier planting. In 1955, yields were mostly above 2,000 pounds per acre. In 1956, however, where maximum yields were rarely above 2,000 pounds per acre, the May 15 and June 27 plantings were simi- lar in yield, considering the varieties of Groups O, I and II (table 10). In 1955, the May 16 planting required eight irri- gations after planting, and the later plant- ing three. In 1955, oil content was 3.0 to 3.5 per cent higher with the earlier seeding date, and protein content lower by the same amount. Within each seeding date, earlier- maturity groups had slightly higher levels of both oil and protein. In 1956, the earlier planting date had slightly higher oil content and slightly lower protein content. Row spacing. A vast amount of experience in the U. S. soybean-growing areas indi- cates that rows 20 to 24 inches apart will yield 10 to 15 per cent more than will wider spacings. In the South, however, where branching is more extensive, yields in wider row spacings have not been re- duced even up to spacings of 40 inches (Hartwig, 1954). Because irrigation is required in Cali- fornia farmers growing soybeans use single rows usually spaced 28 to 30 inches apart. Where double-row beds are used, row spacings are 12 to 16 inches on the bed and 24 to 28 inches over the furrow, with a total of 40 inches between centers of beds. Because of salt accumulation at the top of beds in the Imperial Valley, rows Table 7 YIELD AND OIL CONTENT OF SOYBEANS SOWN AT DIFFERENT DATES AT THE WEST SIDE FIELD STATION, FIVE POINTS, 1966 Number of varieties* Yield Oil contentf Maturity Seeding dates Seeding dates May 25 June 8 June 22 May 25 June 8 June 22 lb. per acre per cent I 2 962 788 758 21.8 21.6 21.8 11 4 1067 894 832 21.3 21.8 22.0 III 3 1160 904 774 20.6 22.2 22.9 IV 3 1292 951 728 20.0 22.5 23.7 V 1 988 574 487 19.2 19.9 19.3 "Group I = A-100 and Chippewa 64; Group II = Adams, Harosoy 63, Hawkeye and Lindarin; Group I Shelby and Wayne;GroupIV = Clark 63, Delmar and Kent;GroupV = Hill. fBasis 10% moisture. Adelphi [22] Table 8 YIELD OF SOYBEANS SOWN AT DIFFERENT DATES AT THE WEST SIDE FIELD STATION, FIVE POINTS, 1967 Maturity group Number of varieties" Seeding dates Maturity Apr. 13 May 15 June 6+ June 22f July 17 group average 1 11 III IV 2 2 1 1 1154 1573 1341 1530 1890 1561 1128 1532 1397 1306 1083 1106 906 991 974 1124 1326 1531 1169 1289 1418 1346 1087 Seeding date average^ 1359 1680 1433 1003 1286 1353 "Varieties were: Group I Clark 63. flnsect damage severe. ^For groups I, II, and III only. A-100 and Hark; Group II — Amsoy and Harasoy; Group III — Wayne; Group IV Table 9 YIELD AND OIL AND PROTEIN CONTENT OF SOYBEANS SOWN AT TWO DATES, DAVIS, 1955 Maturity group Number of varieties Sown May 16 Sown July 2 Yield Oil Protein Yield Oil" Protein lb. per acre per cent lb. per acre per cent 16 2445 21.0 39.8 2339 18.0 42.0 I 5 2967 21.5 39.7 2184 17.8 42.2 II 16 2571 21.1 37.2 2083 17.4 41.2 III 10 2196 20.4 38.2 - - - IV 14 1327 20.0 38.5 - - - 'Basis 10% moisture. Table 10 YIELD AND OIL AND PROTEIN CONTENT OF SOYBEAN VARIETIES SOWN AT TWO DATES, DAVIS, 1956 Maturity group Number of varieties Sown May 15 Sown June 27 Yield Oil° Protein" Yield Oil" Protein" lb. per acre per .eni lb. per acre per cent 17 1632 20.5 40.3 1601 19.6 41.1 I 9 1399 20.1 41.1 1532 19.6 41.7 II 19 2010 — - 2028 - - III 16 1548 - - - — - IV 16 1854 - - - - - 'Basis 10 r 'c moisture. there are sometimes located on the shoul- der or side of sloped beds. Two experiments involving plant and row spacings were conducted in the Im- perial Valley, one in 1954 and one in 1957. In both experiments, seed yield was little affected by increasing plant popula- tions within rows ranging from 20 to 40 inches apart. The narrower between-row widths increased yields 6 per cent in the earlier experiment and decreased it 7 per cent in the later. The plants compensated for the different between-row spacings in several ways. Branching increased from 1.8 branches per plant in the 20-inch between-row spacing to 3.16 branches in the 40-inch rows. Seeds per pod were re- duced from 2.5 at the wider row spacing to 1.2 at the closer ones. At plant spac- ings of 8.4 plants per foot, 3.7 plants failed to develop at the 20-inch between- row spacing and 1.9 plants at the 40-inch. [23] Table 11 PLANT HEIGHT. YIELD. AND OIL AND PROTEIN CONTENT OF SOYBEAN VARIETIES SOWN AT DIFFERENT RATES. DAVIS, 1955» Variety Chippewa Chippewa Chippewa Chippewa Hawkeye Hawkeye Hawkeye Hawkeye Number plants Plant height Yield Seed analyses Seeds sown Gilt Proteint per 6 foot in. //). per acre per cent 5.6 46 2 - 1 9 5 36.4 12 10.1 51 2181 L9.4 35.1 18 9.4 44 2259 19.4 36.0 24 12.5 46 2144 21.1 35.9 6 5.8 57 2>4h is 9 34.6 12 10.5 50 2102 19.0 34.5 18 11.4 4s 2093 is 7 35.6 24 14.0 51 is 7 35.9 "Date sown: May 16: irrigations: 3, treated with a miticide Julj 6 and Hawkeye September 25. fBasis lCr moisture. mil date mature Chippewa September 10, Seed size was unaffected by between-row spacing. Per cent oil tended to increase and protein to decrease at the wider be- tween-row spacings. In one test at Davis in 1955, the vari- eties Chippewa and Hawkeye were sown at between-row spacings of 12, 18. 24, and 30 inches, with about 8 plants per linear foot of row. Early defoliation by mites caused low yields, more so in Hawkeye because it matured later. Hawkeye w.is equally good at all spacings (900 to 950 pounds per acre), apparently because it grew taller and filled in the area between rows at all spacings. Chippewa, being shorter and arrested early in development by mites, was unable to fill in the area between the rows. As a consequence, yields were reduced as spacings increased (1300 pounds per acre at 12-inch rows, and Sin pounds per acre at 30-inch row spacings). Rale of seeding. Recommended rates of seeding in the U. S. soybean-growing areas are about 55 pounds per acre lor 40-inch i,,us. 65 pounds per acre lor 30-inch rows, and 75 pounds per acre for 20-inch rows. This works out to an average of about 10 seeds per loot of row, irrespective of be- tween-row spacing. Experience in Cali- Eornia supports this recommendation. However, in more- productive environ- ments in the Midwest where excess vege- tative growth and early lodging may be a serious problem Lower seeding rates (6 to s seeds per loot ol row) may be more de- sii able (( iooper, 197 1). In a test .it Davis in 1955, yields showed no significant differences where plant spac- ings ranged from about 6 to M plants pei Fool ol io\v and tows were 30 inches Tabi i 12 NITROGEN UPTAKE, SEED YIELD, AND DRY-MATTER PRODUCTION OF UNINOCULATED AND INOCULATED SOYBEANS WITH AMMONIUM NITRATE APPLIED AT DIFFERENT RATES, USDA SOUTHWESTERN IRRIGATION FIELD STATION, BRAWLEY, 1955 Lee soybean seed Nitrogen applied" Leaf colort Numbei <>l nodules^ Nitrogen uptake Seel yield Dry matter Uninoculated Inoculated Uninoculated lb. per acre 60 120 7.2 9.1 7.8 9.2 8.4 9.3 5.5 1 9 4.7 lb. pe 84 LSI SI. L63 1 1 3 173 acre 744 1H74 912 1566 984 1674 tons per acre 3.0 3.7 3.3 3.6 Uninoculated Inoculated 3.6 4.1 "Nitrogen applied in split application, 'A preplant, l A at mid-vegetative stage fScore of 1 = yellow and 10 = dark green on October 26 at late podding. $Score of = no nodules, 10 = many large nodules. [24] apart. At seeding rates of 18 to 24 seeds per foot of row the stems of the plants were thin, with consequent lodging. At plant populations above 8 plants per foot of row there was some natural thinning which increased as the population in- creased (table 11). Rates of seeding had no significant effect on oil and protein content. Results were similar in an experiment conducted at Davis in 1956. Blackhawk, Hawkeye, Chippewa, and Harosoy varie- ties at seeding rates of 6, 12, and 18 seeds per foot in rows 30 inches apart, averaged 1614, 1614, and 1674 pounds per acre respectively. Oil and protein contents showed no consistent changes with differ- ent rates of seeding. Results from experi- ments in other areas of California have been about the same. Gaps up to 8 inches in the row do not reduce yield significantly. The plants on each side of the gap compensate by branching. Depth of seeding. Optimum depth of seeding varies considerably with date of seeding, temperature, texture of the soil, and amount of moisture present. In gen- eral, the seeds should be sown into firm, moist soil to about 1 inch or no more than 2 inches. Moist soil should be pressed closely around the seed, but it should not be packed. For example, a rubber packing wheel providing 7 pounds of pressure per square inch when seed was sown to a depth of 2 and 3 inches, has reduced stands 20 to 25 per cent. Planters should be designed to leave the surface soil loose. Ideal planting conditions are often diffi- cult to achieve where high temperatures and low humidities prevail at planting time; as a consequence, farmers have de- vised various techniques to provide good conditions for the germinating seed, some of which are described below. In the Imperial Valley success has been best with plantings 2 to 2\/ 2 inches deep into a firm, moist seedbed, if a quick furrow irrigation is given no later than 2 days after planting. The early-post- planting irrigation prevents the soil from drying out in the region of the seed and also lowers soil temperatures. Without the irrigation the temperature at a depth of 2i/o inches was 80 to 100° F. An irrigation lowered temperatures 10° F. The stand was 95 per cent with an irrigation and 75 per cent without it. In the San Joaquin Valley a technique used for cotton has been successful with soybeans. Rough beds are put up and a furrow irrigation provided before plant- ing. When the soil is dry enough to work the beds are reshaped and soybeans planted immediately, usually Avith one machine. In this way the top of the bed is very moist and germination occurs quickly. In June (when high temperatures prevail) an irrigation within 2 days after sowing will improve stands. Inoculation. As a general rule, soybean seed should be inoculated with Rhizobhim bacteria of the type required especially for soybeans. It is an absolute necessity that the seed be inoculated the first time the crop is sown in a field, and it is usually advisable to inoculate again if more than a year has passed since the last time soybeans were grown. Because soybean inoculum is not widely used regularly in California, arrangements for its purchase and delivery should be made at the time of seed purchase. Inoculum usually appears as a dry black dust, which is mostly organic matter. A special southwest (SW) inoculum was de- veloped for the Imperial Valley by mix- ing seven of the strains which gave the best nodulation and plant response in that area (Abel and Erdman, 1964). The Southwest inoculum has been satisfactory elsewhere in California, although it has not been compared critically with inocu- lum developed for other areas, except in the Imperial Valley. Only fresh inoculum should be used, and it should be stored in a cool place prior to use. Inoculum stored in a cool place for a year or more, or subjected to temperatures above 80 to 90° F for 10 to 12 hours, or left uncovered in bright sun- light for even a short time, will be non- viable. Therefore only a limited amount of seed should be inoculated at one time. This may be done by sprinkling y 4 to 1 pint of water on 60 pounds of seed in a washtub; the recommended amount of inoculum is then added and stirred until all seeds are almost black with inoculum. Because the water makes the seed coat soft, [25] Nodulation patterns of soybean roots. Left pair: no nodulation. Center pairs: limited nodulation after seed inoculation. Right pair: general nodulation from Rhizobium in soil before planting. seed is placed in the planter boxes in small amounts and sown immediately. Inoculated seed should be kept cool and covered with a damp cloth. If inoculum is applied as a dust to dry seed, the amount should be doubled. Roots should be examined about 2 weeks after the seedlings emerge, to see whether small nodules are present. Lift the roots and soil carefully with a shovel and wash the soil away. If the bacteria are in the soil at seeding time, nodules will be distributed over all of the surface roots. If the bacteria are not present in the soil and seed inoculation is the only source of the Rhizobium, nodulation will be abundant only in the region of the germinated seed. Nodules that furnish nitrogen to the plant appear pink when sliced open; ineffective nodules are white. As few as three or four large nodules will be adequate for good growth. If inocula- tion fails, and no nodules are found, about 80 pounds of nitrogen should be applied promptly as a side dressing. The benefits of inoculation will depend on the level of soil fertility. In an experi- ment in the Imperial Valley on soil with low levels of available nitrogen, inocula- tion nearly doubled yields. Even with ap- plications of nitrogen fertilizer at 60 and 120 pounds nitrogen per acre, yields were much increased by inoculation (table 12). On fertile soil at Davis where yields have varied between 1600 and 2000 pounds per acre without nodulation, inoculation had little or no beneficial effect on yield in experiments conducted in 1955, 1956 and 1957. This was true whether comparisons were made with or without the addition of nitrogen and phosphorus fertilizer. In those experiments inoculation did not af- fect oil and protein contents in a consistent manner but generally lack of nodulation results in a higher oil and a lower pro- tein percentage compared with beans from [26] Table 13 EFFECT OF NITROGEN FERTILIZATION AND DIFFERENT INOCULATION PROCEDURES ON NODULATION, YIELD, AND OIL AND PROTEIN CONTENT OF SOYBEANS, DAVIS, 1957 Rhizobium seed treatment Nitro- gen applied Nodul- ation" Yield Oil contentt Protein contentt Chip- pewa Black- hawk Av- erage Chip- pewa Black- hawk Av- erage Chip- pewa Black- hawk Av- erage lb. per acre lb. per acre per cent None 1890 2058 1974 16.2 14.7 15.4 39.7 40 2 40.0 Dry 6 1650 2178 1914 16.6 17.3 17.0 40.5 40.1 40,3 8 1674 2028 1851 16 1 17 16 6 40 5 39 4 40 Water and honeyt 9 1812 2208 2010 17,3 15.3 16.3 40.9 40.4 40.6 Water and honey:}: 40 5 1698 2244 1971 17.2 14.6 15.9 40.4 40.0 40.2 Water and honey:}: 80 5 1560 2202 1881 17.4 17.5 17.4 41.4 40,3 40.9 Score of = no nodules , 10 = ri nany lar ie nodules. tBasis 10 p/ r moisture. £10 to 1 by weight. well-nodulated plants. In 1957, the addi- tion of nitrogen fertilizer depressed nod- ule formation, and the addition of honey to the inoculating solution had no appre- ciable effect (table 13). At Davis in 1955, several strains of Rhizobium were tested for their ability to produce nodules on the Lee variety. In the absence of inoculation no nodules were produced, plants were light green in color, and 112 days after seeding the yield of hay was 7940 pounds per acre with a protein content of 11.6 per cent. All Rhizo- bium strains produced nodules, and plants were dark green. Where a composite rhizo- bial strain was used, yield of hay was 7760 pounds per acre, and protein content 14.6 per cent. Apparently, good nodula- tion can increase protein content of the hay without affecting yield. An experiment at the West Side Field Station illustrated the relationship be- tween the application of nitrogen and nodulation. Different rates of nitrogen fertilizer (ammonium sulfate) were applied before sowing, at flowering, or at both times. A barley crop was harvested just Table 14 MEAN NUMBER OF NODULES PER SOYBEAN PLANT AFTER FERTILIZATION WITH AMMONIUM SULFATE AT DIFFERENT RATES AND DIFFERENT TIMES, WEST SIDE FIELD STATION, FIVE POINTS, 1968 Applications of nitrogen Mean number of nodules per plant Time Pounds per acre Straw burned Straw not burned Nitrogen rate average Preplant 17.5 15.4 16.5 50 5.2 2.2 3.7 100 1.8 6.8 4.3 150 2.2 4.4 3,3 6 7 7 2 6 9 o + o — o 7.9 23.2 15.6 + 50 = 50 7.9 19.0 13.5 50 + 50 = 100 5.7 9.4 7.6 50 + 100 = 150 1.5 8.6 5.1 5.8 15.1 10 4 12 24 6 18 3 50 17.4 21.2 19.3 100 13.5 21.8 17.7 150 4.4 15.2 9.8 11.8 20.6 16 3 "Differences due to time of application significant at 5% level; differences due to rate of application significant % level. [27] before seeding the soybeans. On one-half of the area the barley straw was burried. On the other half of the area the straw was shredded and left on the ground. Applications of 50 or more pounds of nitrogen before planting reduced the number of nodules (table 14). Delayed application of nitrogen was associated with significantly higher nodule counts. However, applications of 150 pounds of nitrogen at flowering time also reduced the number of nodules. Burned and unburned areas were not significantly different in nodulation (Beard and Hoover, 1971). Fungicidal seed treatment. Where good quality seed with a high germination is used there has been little or no benefit in California tests from treating the seed with a fungicide. If poor seed is used, however, seed treatment has resulted in better stands. Most seed-treatment chemi- cals are toxic to Rhizobium bacteria. Thus, they can reduce the effectiveness of seed inoculation, but when used at recom- mended rates they have no effect on Rhizobium bacteria already present in the soil. Where it appears that both fungi- cidal seed treatment and inoculation are essential, best results have come from applying the fungicide first to the seed, followed by the Rhizobium, with planting following shortly thereafter. Consult the current pest control guide for recom- mended chemicals and rate to use. WEED CONTROL B. B. Fischer, W. A. Harvey Weed control is essential to economical soybean production. Weeds not only com- pete for moisture, nutrients, and space but also serve as hosts to insects and disease organisms which can damage the crop. Weed control is the major cost item in crop production in many soybean-grow- ing areas, and numerous investigators have demonstrated the harm that annual weeds have on the growth and yield potential of soybeans. Weedy fields were subject to yield re- duction, delayed maturity, increased lodging and poor harvesting conditions. Studies also showed that plant height, maturity, number of pods, seeds per pod, and seed weight were adversely affected by weeds. For further background on weed control in soybeans consult the following references (Burnside and Col- ville, ]964a,b; Kust and Smith, 1969; Peters, et al, 1959; Peter? el al, 1965; Ray, 1961; Staniforth and Weber, 1956; Stani- forth et al, 1963; Wax and Pendleton, 1968; Wiggins, 1939). Weed species Most research on soybean weed control in California was done in the San Joaquin Valley. Weeds generally the most trouble- some in that area include: Redrool pigweed Amaranthus retro flex us L. Lambsquarters Chenopodium album L. Barnyardgrass Echinochloa crusgalli (L.) Beauv. Prickly lettuce Lactuca Serriola L. Annual sowthistle Sonchus oleraceus L. Lance leaf groundcherry Physalis lanceifolia Nees. Hairy nightshade Solatium sarrachoides Sendt. ex Mart. Cocklebur Xanthhun stru murium L. var. carta- dense (Mill.) T. & G. Common sunflower ^ Helianthus annuus L. Tall morning glory Ipomoea purpurea (L.) Roth. Tolguacha Datura meteloides A. D.C. Potato family Solanaceae Puncture vine Tribulus terrestris L. [28] Principles of weed control A good weed-control program includes the following: • Proper selection of a field free of per- ennial weeds. • Good seedbed preparation to facilitate uniform planting and later cultivations. • Proper planting to ensure uniform emergence and allow early cultivation. • Proper row spacing (rows 30 inches or narrower offer greater weed competi- tion). • Adequate plant population within the row (close spacing of soybeans in the row encourages rapid growth). • Proper fertilization and irrigation to ensure a vigorously growing crop that competes strongly with weeds. Briefly stated, weed control must be an integral part of the entire production or management system to be effective. Mechanical weed control An effective method of weed control in soybeans is timely cultivation with prop- erly adjusted tools. Emergence and rapid growth of weeds in the planted row can offer severe and early competition. Shallow working of the soil with rotary hoes, with tines reversed, will control weeds in their seedling stage of growth. Reversed disk-hillers and bed knives can also be used effectively when the beans are small, and breaking up the top i/o to 1 inch of soil will also kill weeds. Finger- type weeders properly adjusted to operate under a shallow layer of soil can be used to remove seedling weeds, espe- cially grasses, from the planted row when beans are well established (2 inches or taller). Rubber weeders similar to finger- type weeders but made of rubber can also be used; both these devices work best in lighter soils. Sectioned rolling cultivators are found to be effective and versatile cul- tivating tools where beans are on beds or flat-planted in rows. Effective mechanical weed control de- pends on timeliness of operations. The younger the weeds the more easily they are dislodged and destroyed by cultiva- tion. Adverse weather conditions or irri- gation schedules can make effective mechanical weed control difficult or im- possible because soil is too wet or too dry. Selective herbicides have greatly improved weed control in soybean fields. Chemical weed control Investigators in the Midwest states have found that residual pre-emergence herbi- cides are as effective as timely shallow cul- tivations, and are superior when rainfall delays cultivation. Most published data summarize soybean weed control research conducted in areas where natural precipitation follows soy- bean planting; under these conditions surface applied pre-emergence herbicides performed effectively. Herbicides regis- tered for use in soybeans are shown on page 33; this list will change as new herbicides are developed and older ones abandoned. To obtain effective weed control from surface application the herbicide must be leached by water into the soil where weed seeds germinate. Rain or sprinkler irriga- tion is effective for leaching the herbicide, but furrow irrigation has not been suc- cessful. In California the weed control obtained with surface-applied pre-emer- gence residual herbicides has been erratic and unpredictable. California studies 1966-67 During the 1966 and 1967 growing sea- sons selected herbicides were evaluated under varied methods of land preparation, soil incorporation, and furrow and sprin- kler irrigation. These studies further demonstrated that incorporation of her- bicides is essential for effective weed control under furrow irrigation. Incorpo- ration with power-driven rotary tillers gave the most effective control. Sectioned rolling cultivators gave as effective control when two passes were made over the same area (in opposite directions) as did in- corporation with disks to a depth of 3 to 4 inches prior to listing. Tolerance of soybeans to the herbicides used was equally good regardless of the incorporation tools employed. Vernolate, chlorpropham, diphenamid, and a com- bination of diphenamid and trifluralin gave the most effective volunteer barley control. Weed control with vernolate was [29] Table 15 EFFECT OF DIFFERENT HERBICIDES ON NUMBER OF VOLUNTEER BARLEY PLANTS AND SOYBEAN PLANTS COMPARED WITH UNTREATED PLOT, WEST SIDE FIELD STATION, FIVE POINTS, 1966° Application ratet Effect on volunteer barley Effect on soybeans Number of plants per plot Per cenl of untreated pIot§ Herbicide On bed In furrow Number of plants Trifluralint ........ Chlorprophamt Chlorpropham Vernolate Amiben® Untreated 0.75 3.0 4.0 3.0 3.0 11 3 4 8 28 9a 17ab 19ab 67 cd lOOe 24a 57b 90 be 100c 100c 106 87 90 94 110 "Harosoy 63 soybeans sown July 28 after a crop of California Mariout barley. Barley straw and broadcast herbicide applications incorporated by discing. Beds made on 30-inch centers in July, 1966. tTrifluralin and chlorpropham were used in a combination treatment at rates shown by first two figures in the next column. ^Active ingredient in pounds per acre. §Values followed by the same letter do not differ significantly. (P = <0.05) Duncan's multiple range test. markedly better with incorporation by power-driven rotary tillers. Early growth of soybeans was retarded in areas treated with chlorpropham, alone or in combination with trifluralin (table 15). Vernolate also caused early growth retardation, plus some deformity (fusion) of the leaflet on the first true leaves. The retardation caused by these herbicides was short-lived; a month follow- ing crop emergence it was not discernible. Amiben®, DCPA, and propachlor failed to give adequate volunteer barley control. As expected, residual control was short with chlorpropham and vernolate. Five to six weeks after treatment, summer annual weeds (primarily pigweeds, lambsquar- ters, and barnyardgrass) were germinating and growing in the treated areas. California Studies, 1968-69 It was envisioned that soybeans in the San Joaquin Valley will be grown in a double- cropping system following barley or, pos- sibly, wheat. Attention was therefore focused on controlling volunteer barley. Varied methods of soil preparation were employed, with emphasis on minimum soil manipulation following barley harvest. Chlorpropham and diphenamid were the only herbicides used because of their effec- tiveness in controlling volunteer barley. The performance of these herbicides was evaluated in plots where barley stubble and straw were burned, and in unburned areas. In the unburned areas the thorough- ness with which the straw and stubble were incorporated into the soil varied with the method of soil preparation (pages 19-20). The herbicides were evaluated in pre- irrigated plots and in plots where the crop was planted in dry soil and then irrigated. Burning straw and stubble greatly re- duced the volunteer barley population. Effectiveness of burning varied with the quantity of straw present and the intensity of the fire. Where straw was sparse, control was poor. Postplant surface-applied herbi- cides under sprinkler irrigation performed much better in the burned areas than in the straw-mulch areas. Diphenamid gave somewhat better control than chlorpro- pham when applied postplant and sprin- kler-irrigated. The most effective control was obtained when the herbicides were incorporated 2i/o to 3 inches deep, in a 12-inch band with a power-driven rotary tiller (tables 16, 17). This method was effective in both burned and unburned areas when the barley was planted on 30-inch beds and the soil left undisturbed until the herbicide was applied and in- corporated. Chlorpropham gave somewhat better control when incorporated with sectioned rolling cultivators. Two passes over the same area, made in opposite directions, gave better control than a single pass. Where barley was planted on 30-inch beds, control was improved by working the beds with sectioned rolling cultivators once prior to herbicide application. Emergence of seedlings was more rapid and uniform in both herbicide-treated and [30] Table 16 EFFECT OF HERBICIDES ON NUMBER OF SOYBEAN AND VOLUNTEER BARLEY PLANTS FOLLOWING DIFFERENT SEEDBED PREPARATIONS, WEST SIDE FIELD STATION, FIVE POINTS, 1968° Appli- cation ratet Method of incorp- oration^: Number of plants§ Burned area Straw-mulch area Herbicide Soybean Barley Soybean Barley Chlorpropham Chlorpropham Chlorpropham Diphenamid Diphenamid Diphenamid 4 4 4 5 5 5 Power Rotary None Power Rotary None Power Rotary None 51 56 58 53 56 60 57 79 62 3 4 30 16 11 4 16 22 19 51 58 37 41 53 30 42 50 23 1 2 6 15 13 17 18 18 Untreated 7 "Wayne soybeans sown July 3 after a crop of California Mariout barley. Barley seed was broadcast and beds made on 30-inch centers in November, 1967. Barley straw and stubble was burned on half of test area, and was mulched with a flail type cotton stalk chopper on other half. fActive ingredient in pounds per acre. t-Power = power-driven rotary tiller operating at 2Vi mpb, with incorporation 2.5 to 3.0 inches deep; rotary = sectioned rolling cultivators. None = unfilled, surface application. §Counts were made in a 6-inch band 8 feet long over center of bed. untreated areas when the soybeans were planted in dry soil and irrigated up. Un- controlled volunteer barley attained a height of 12 to 20 inches before heading out, and produced 6 to 18 seeds per head. The effect of this competition on soybean growth and vigor varied with the density of the barley population. Timely cultiva- tions can control volunteer barley unless repeated irrigations are needed. After secondary roots develop on the barley re- moval is difficult, especially from the planted row. California studies, 1970 Wayne variety was seeded on June 25th, and effect of the herbicides was evaluated on July 14th and 28th. Some herbicides did not injure soybeans, while others pro- duced severe injury. There were also large differences between the effectiveness of the herbicides in controlling the volunteer Table 17 EFFECT OF HERBICIDES ON STANDS OF VOLUNTEER BARLEY AND YIELD OF SOYBEANS FOLLOWING DIFFERENT SEEDBED PREPARATION, WEST SIDE FIELD STATION, FIVE POINTS, 1969° Appli- cation ratet Method of incorp- oration^ Barley stand§ Soybean yieldll Herbicide Burned area Straw-mulch area Burned area Straw-mulch area Chlorpropham Chlorpiopham Chlorpropham Diphenamid Diphenamid Diphenamid Untreated Untreated Untreated 4 4 4 5 5 5 Power Rotary None Power Rotary None Power Rotary None 10 10 35 28 18 45 50 53 50 8 8 55 30 38 58 93 80 70 1540 1560 1300 1340 1300 1560 1320 1440 1160 1020 1380 1460 1500 1240 980 1440 1240 1540 "Kent soybeans sown June 19 after a crop of California Mariout barley. Barley seed was broadcast and beds made on 30-inch centers in November 1968. Barley straw and stubble was burned on half of test area, and mulched with a flail-type cotton-stalk chopper on other half. Soybeans harvested October 25, 1969. fActive ingredient in pounds per acre. t-Power = power-driven rotary tiller operating at 2Vs mph, with incorporation 2.5 to 3.0 inches deep; rotary = sectioned rolling cultivators. None = unfilled, surface application. §Stand of barley in per cent of a solid stand which would rate 100 c 'r. 1 1 Yields not significantly different. [31] Table 18 EFFECTS OF VARIOUS HERBICIDES ON SOYBEANS AND VOLUNTEER BARLEY, WEST SIDE FIELD STATION, FIVE POINTS, 1970 Herbicides Application rate§ Effect on soybeans Effect on barley Number of plants Aug. 14|| Injury evaluation Aug. 14H Number of plants Aug. 14|| Control evaluation Aug. 28H Alachlor Alachlor Chloroxuron . . . Chloroxuron Norea Norea VCS438 VCS438 Diphenamid Trifluralin" Diphenamid" Chlorpropham Chlorprophamf Trifluralinf Chlorpropham $ SD30l87t SD3018 ER5461 Untreated 2.0 4.0 2.0 4.0 2.0 4.0 2.0 4.0 6.0 0.25 4.0 4.0 2.0 0.75 2.0 0.75 0.75 0.75 23.6a 22.3a 21.3a 19.3a 15.0b 18.6a 14.3b 6.0c 20.3a 19.0a 18.0a 21.0a 18.0a 15.0b 19.3a 19.6a 0.6 1.0 0.6 6.0 7.6 2.6 1.6 0.6 2.0 1.6 1.3 8.6b 8.3b 9.6b 4.3b 17.3d 13.0c 8.3b 6.3b 3.6a 7.0b 3.3a 3.3a 4.0a 15.6c 5.6a 23.0d 6.6 6.6 2.3 5.6 3.0 6.3 7.0 9.0 9.0 9.0 9.0 2.3 4.6 1.3 "Trifluralin and diphenamid were used in a combination treatment at rates shown in adjacent column. fChlorpropham and trifluralin were used in a combination treatment at rates shown in adjacent column. t Chlorpropham and SD 30187 were used in a combination treatment at rates shown in adjacent column. §Active ingredients in pounds per acre. llCounts were made in a 6-inch band 4 feet long over center of bed. Values given are from two areas in each plot for three replications, and are estimates of the average number of plants in 4 feet of row. Values followed by the same letter do not differ significantly (P = 0-1 ft. 1-2 2-3 3-4 -11 9 65 95 10 15 'Data of J. R. Stockton (deceased) Department of Water Science and Engineering, University of California. Davis. [35] cent; 8 to 16 inches, 35 per cent; 16 to 24 inches, 50 per cent; 24 to 36 inches, 90 per cent (data of George H. Abel, unpub- lished). Water requirements In irrigation planning and practice it is useful to know the rate of water loss from the cropped area by evaporation and transpiration. However, if complete in- formation is lacking, knowledge of the time and magnitude of maximum use along with the total seasonal requirement will be valuable. Data for soybeans are limited, and estimates must be reinforced by comparison with data from other crops grown about the same time, as well as by study of climatic and plant factors in- fluencing evapotranspiration. The Chippewa variety at Davis, planted July 1, used 19 inches of water for the entire season. At Shafter, six irrigations estimated at 3 inches of water per irriga- tion, appeared to adequately supply the crop (data of J. R. Stockton, unpublished). No accounting was made of water stored in soil at planting, but this can be dis- counted because the first irrigation was applied very early before much water use by the crop. The peak use rate was 0.28 inch per day in early August, a value probably similar to that of other crops at the same time. In West Side Field Station experiments, 15 inches of water applied during the cropping season produced near-maximum yields. A 12-inch prcirrigation was ap- plied before seeding. The fraction of the preirrigation water used by the crop was not measured, but could not have been more than a few inches. Thus, water use of 18 to 22 inches seems reasonable. Data for water use at Davis have been compared with those for pink beans, blackeyes, and grain sorghum — crops com- monly planted in early June. The seasonal water use for all these crops is similar, ranging from 18 to 22 inches. Planting date probably has appreciable influence. In the July 1 planting at Davis, maximum vegetative development was not reached until late August when potential evapotranspiration is appreciably below the peak reached under full plant cover in June or July. Thus planting on June 1 might increase seasonal water use by 3 or 4 inches. All available evidence indicates that seasonal water use for soybeans in the Sacramento and San Joaquin Valleys is 20 to 24 inches, with lower values within that range applicable to earlier-maturing varieties and late planting. In an Imperial Valley test, estimates of water applied ranged from 28 to 39 inches including two irrigations for establish- ment of stand from planting and replant- ing. Yield differences, while statistically significant, were not great (data of George H. Abel, unpublished). On the basis of these data and comparison of climatic factors influencing evapotranspiration with those of the Central Valley, an ap- proximate estimate of seasonal water use for the Imperial Valley is 25 to 30 inches. Responses to irrigation treatments Tables 21 to 28 give data on various re- sponses to differential irrigation treat- ments at five locations. A wide range of soil conditions are represented, and the climatic differences between locations at Davis and Brawley are appreciable. At Davis the tests were on Yolo soil, a deep alluvial clay loam. The available wa- ter storage capacity of the soil is moder- ately high (approximately 1.5 inches water per font of soil) and the subsoil readily penetrable by roots. In Experiment Davis- 1 (table 21), the treatment receiving 10 ir- rigations was irrigated weekly beginning 1 weeks after planting. The 2-irrigation treatment was irrigated after an observable retardation of growth but prior to wilting. The 1 -irrigation treatment was watered 1 week after the first irrigation of the 2-irri- gation treatment. The 3-irrigation treat- r ment was irrigated at weekly intervals prior to flowering with no irrigations after onset of flowering. For Experiment Davis- 2 (table 22), irrigation interval for the most frequently irrigated treatment was 10 to 12 days. The 2-irrigation treatment was applied at observable growth retardation. At Five Points, the Panoche clay-loam soil is deep alluvium with high available [36] Table 21 EFFECTS OF IRRIGATION TREATMENTS ON CHIPPEWA VARIETY PLANTED JUNE 8, 1957, EXPERIMENT DAVIS-1 Number of irrigations Plant height Weight of 100 seeds Yield Lodged in. gm. lb. per acre per cent 10 42 20.0 2204 65 3 43 18.1 1988 35 2 42 17.8 2296 5 1 42 17.1 1923 3 Table 22 EFFECTS OF IRRIGATION TREATMENTS ON CHIPPEWA VARIETY PLANTED JULY 1, 1958, EXPERIMENT DAVIS-2 Number of irrigations Plant height Pods per plant Weight of 100 seeds Yield Lodged Maturity date in. gm. lb. per acre per cent 6 37 17. 4 17. 2 1588 40 11/5 2 35 20.5 15. 1 1712 10 10/20 31 15. 5 11. 6 1092 10/3 Table 23 EFFECTS OF IRRIGATION TREATMENTS ON THREE SOYBEAN VARIETIES PLANTED MAY 26, 1966, EXPERIMENT FIVE POINTS-1 Number of irrigations Chippewa Clark Wayne Yield Oil Protein Yield Oil Protein Yield Oil Protein lb. per acre per cent lb. per acre per cent lb. per acre per cent 5 1650 19.8 48.5 1790 17.6 46.5 2060 19.7 47.6 3 1580 20.2 48.0 1580 17.6 46.2 1905 19.7 46.4 1 995 20.4 44,3 1005 21.9 42.4 1115 20.5 42,3 water storage capacity (2 inches per foot). Physical retardation of root growth is prob- ably slight, but the salinity and boron lev- els are high enough to affect plant growth and possibly root development. The 5-, 3-, and 1-irrigation treatments of Experiment Five Points- 1 (table 23) were applied when soil moisture levels were at approximately 50, 35, and 10 per cent available moisture at the 18-inch soil depth. A 12-inch preirri- gation was applied, and treatments re- ceived respectively 22, 15, and 5 inches of irrigation water during the cropping sea- son. For experiment Five Points-2 (table 24), irrigations were applied at 65, 50, and 35 per cent residual available moisture at the 18-inch soil depth for, respectively, treat- ments receiving four, three, and two irri- gations. A 12-inch pre-irrigation was ap- plied, followed by 16.5, 14.5 and 11 inches during the growing season. Mite infesta- tion was severe but not uniform in the area. (For additional details of these two experiments see Miller and Beard, 1967.) The Shafter experiment (table 25) was conducted on Hesperia sandy loam of low available water storage capacity (about 0.7 inch per foot), readily penetrated by roots. The 6-irrigation treatment was irrigated at 2 week intervals, while in the 3-irriga- tion treatment watering was delayed until plants wilted. Soil characteristics are not available for the site of the Corcoran Experiment (table 26). However, the soils of the vicinity are clay loams and clays with variable sub- soils. The 5-irrigation treatment was first irrigated 24 days after planting and sub- sequently at 17, 14, and 21 day intervals. [37 Table 24 EFFECTS OF IRRIGATION TREATMENTS ON TWO VARIETIES PLANTED MAY 25, 1967, EXPERIMENT FIVE POINTS-2 Number of irrigations Clark Wayne Yield Oil Protein Yield Oil Protein //;. per acre per cent lb. per acre per a nt 4 990 19.3 47.3 1194 19.3 47.2 3 966 20.1 46.3 1110 19.0 47.7 o 624 18.9 46.2 660 19.2 46.4 The 4-irrigation treatment was watered at moderate observed water deficit, and the 3-irrigation treatment was irrigated at wilting. The Brawley experiments were con- ducted on intermixed Holtville silty clay and Holtville clay. Holtville subsoils are typically dense, and soil salinity at levels of 5 to 10 mmhos per cm in the satura- tion extract were measured in the plot area of Experiment Brawley- 1 (table 27). The plants were irrigated up and two subse- quent irrigations applied before differen- tial irrigation treatments were started at age 43 days. The irrigation regimes were classified according to soil moisture ten- sion at 8- or 16-inch depth: wet if subse- quent irrigations were applied at 0.3 bar soil-moisture tension; medium at 2 bars and dry at 6 bars. The irrigation regimes were varied during three periods of plant development. The first period included the remainder of the development prior to flowering, the second period was from the beginning till the end of flowering, and the third included pod formation and seed development. The 12-irrigation treatment was thus characterized as wet-wet-wet and the 1 1-irrigation treatment wet-dry-wet. The first 9-irrigation treatment was termed wet-dry-dry, the second 9 (9M in table 27) as medium throughout, and the 7-irriga- tion treatment dry throughout. Data are averages for all row spacings and in-row plant spacings. In Experiment Brawley-2 (table 28) dif- ferential irrigation did not start until five weeks after planting, and four irrigations had been applied by that time. Subsequent irrigations were applied at 0.6, 2, and 9 bars (presumably at the 8 or 16 inch soil depth) for the 12-, 8-, and 6-irrigation treat- ments. Data for uninoculated treatments are not included, but data are averaged for nitrogen treatments since nitrogen pro- duced little effect on yield. Effect on yields and yield components The effect of irrigation treatment is less at Davis than at any other site. The soil was moist at planting to depths well be- low the potential rooting depth. The root system increases in depth and in degree of proliferation, tapping new sources of water nearly rapidly enough to produce maximum \ields without irrigation or rain- fall. The unirrigated treatment in Experi- ment Davis-2 produced a very satisfactory yield (70 per cent of maximum). One or at most two irrigations produces maximum yield provided the root zone is moist at planting. The Brawley experiments illus- Table 25 EFFECT OF IRRIGATION TREATMENTS ON CLARK VARIETY PLANTED JUNE 11, 1957, SHAFTER EXPERIMENT Number of irrigations Plant height Yield Lodging Maturity date 6 3 LSD 5^ in. 53 49 //>. per acre 2686 1926 4 SO per cent 40 10 10/25 10 20 'Data of J. R. Stockton. [38] Table 26 EFFECT OF IRRIGATION TREATMENTS ON CLARK VARIETY PLANTED JUNE 26, 1957, CORCORAN EXPERIMENT Number of irrigations Plant height Yield Lodging Maturity date in. Ih. jH'r acre per cent 5 39 1469 40 11/3 4 39 17.52 10 11/3 3 36 1510 10 10/29 LSD 5^ 179 'Data of R. T. Edwards and P. F. Knowles. Table 27 EFFECT OF IRRIGATION TREATMENTS ON SOYBEANS PLANTED JUNE 6, 1954, EXPERIMENT BRAWLEY-1° Number of irrigationst Plant height Yield Weight of 100 seeds Oil Protein in. //;. per acre Km. per cent 12 34 1548 10. 21.8 37.2 11 - 1632 10. 21.8 39.2 9 - 1284 - 22.3 36.9 9 M 33 1398 - 22.0 38.0 7 30 1074 8.2 22.3 37.1 LSD 5% 192 "Data of George H. Abel. tSee text for difference in two 9-irrigation treatments. Table 28 EFFECT OF IRRIGATION TREATMENTS ON SOYBEANS PLANTED JUNE 16, 1955, EXPERIMENT BRAWLEY-2* Number of irrigations Plant height Pods per plant Seeds per pod Weight of 100 seeds Yield Maturity date in. Km. lb. per acre 12 24 21.8 2.04 12.0 1722 11/4 8 20 10.8 1.98 11.8 1092 11/5 6 22 17.7 1.97 12.0 1494 11/4 'Data of George H Abel trate the other extreme. The dense subsoil retards root penetration, and the root zone is effectively shallow. The requirement for frequent irrigation is increased by high soil salinity and the somewhat higher rate of transpiration. Production of maximum yields on Holtville clay apparently requires eigth to ten 3- to 4-inch irrigations. Be- cause the soil is effectively shallow, the root zone storage is so low that preirrigation is meaningless except possibly for reducing surface salinity. Furthermore, soybeans in the Imperial Valley generally must be ir- rigated up. The San Joaquin Valley tests show ef- fects of intermediate conditions, but this is probably more determined by soil than by location. The Shafter data are repre- sentative of required irrigation for a sandy soil. The available water storage in the 4 to 5 foot root zone is only 3 to 4 inches, and six 4-inch irrigations would be needed to supply the seasonal requirement. The Five Points and Corcoran soils have mod- erately high storage capacity, but appar- ently retard rate of root penetration or growth is affected by salinity. Under these conditions, seasonal water requirement must be met by moisture in the soil at planting plus three to four irrigations. If water infiltration into soil is slow, depth of water applied per irrigation is small be- [39] cause plants may be damaged if water is ponded too long, and the total number of irrigations must be increased regardless of water-storage capacity and penetrability by roots. In two experiments attempts were made to determine irrigation schedules by foliar darkening; this has been shown to be effec- tive for common beans., but the procedure failed here because foliar darkening was too indefinite. From two experiments (Shatter, Corcoran), it is apparent that de- laying irrigation until wilting reduces yields. Yield component data were collected in only two experiments, and except for seed weight determinations, sampling and counting are so tedius that adequate sam- pling is rarely undertaken. However, the data indicate no major impact of irrigation practice on flowering and seed develop- ment processes under conditions where ex- tremely severe drought is not a factor. Pro- longed moderate drought late in the season does result in shriveled seed and in lower seed weight (as shown in table 21). Although soybeans bloom over a period of nearly a month, there is apparently little tendency to remain vegetative at ex- pense of seed production. Forcing bloom by moderate drought is suggested in the Davis-2 Experiment (table 22) where the higher number of pods per plant indi- cates increased seed set in the 2-irrigation treatment, resulting in higher yield. How- ever, the yield of the most frequently irri- gated treatment was lower than that of an intermediate treatment in only one other experiment (at Corcoran, table 26). Effect on protein and oil content of seed The constituents of major interest are pro- tein and oil. In the three experiments in which oil and protein content were meas- ured there were no clear over-all trends except that irrigation does not markedly influence oil and protein content. Irriga- tion practices that reduce yields will affect seed composition only if seed size is re- duced. The data of Experiment Five Points-1 (table 23) suggest that drought slightly increased oil content and de- creased per cent protein. However, no trend is detectable in other data. Effect on lodging and maturity More frequent irrigation often increases lodging as shown in data from several ex- periments. Lodging generally is not caused as much by breaking or bending of stems as by lack of support at the crown, so that lodging increases with a combination of wind and wet surface soil; more frequent irrigation thus increases probability of lodging. In most experiments the effect on matur- ity was not pronounced, but the Davis-2 experiment shows that moderate but pro- longed water deficits, occasioned by water extraction only from deep subsoil, can hasten maturity date substantially. Degree of shattering was measured in some experiments. The data show that irri- gation treatment had little if any influence. As with other plants, incidence of mite infestation and injury is increased by drought conditions. Summary Soybeans should be irrigated in the same general manner as many other field crops which grow during the same season. They are neither especially sensitive to, nor tolerant of, drought or excess water in soil. Root development is relatively rapid and vigorous, and soybeans can effectively absorb water from soil depths of 5 to 6 feet in deep, easily penetrable soils. The crop consumes 20 to 24 inches of water during the growing season in the central valleys and 25 to 30 indies in the desert areas of California. The portion of this quantity of water not supplied by water stored in the soil at planting must be applied as irrigation. If given less water, yields will be reduced. The number of irrigations required to provide the necessary quantity of water depends primarily on three soil character- istics: the depth, the water storage capac- ity, and penetrability by roots. Experi- ments show that the number of irrigations required for maximum yields may range from two to twelve under varied condi- tions. [40] VARIETAL TESTING AND IMPROVEMENT B. H. Beard, P. F. Knowles Planting the most suitable soybean variety is of paramount importance. In past years many California farmers have been dis- appointed with this crop, partly because they seeded varieties that were either too early or too late for their location. Soy- beans are day-length sensitive (see page 15) and available varieties have a great range of maturity. If a variety is mod- erately late for a particular location, only a few flowers will develop late in the sea- son; if the variety is extremely late there will be no flowers. If a variety is too early for a location it may also produce only a few beans before it matures, or if it flowers during a period of hot dry weather it may not set many pods. For convenience in organization and comparison, soybean varieties are ar- ranged into groups based on the date of maturity. The maturity groups are num- bered 00, 0, and I through VIII, from earliest to latest types, with differences mainly in the vegetative growth period (see page 15). In U. S. soybean-growing areas, different varieties are recommended for areas only 100 to 200 miles apart in the north-south direction. Locations for different maturity groups The probable area of soybean production in California extends north to south for 700 miles (the distance from Ames, Iowa to Shreveport, Louisiana), thus different varieties with a wide range of maturities will be required for satisfactory yield in different areas of the state. The po- tential areas of soybean production in California are somewhat discontinuous and are rather distinct in varietal require- ments. Most if not all of the major vari- eties in the United States and many experi- mental lines have been tested during the 50 years tests have been conducted in Cali- fornia. Seed for many of the tests was sup- plied by the U. S. Department of Agricul- ture through the U. S. Regional Soybean Laboratory, Urbana, Illinois and the USDA Soybean Project, Stoneville, Missis- sippi. During 1967 through 1969 there were 133 different varieties and lines tested in Yolo County, 197 in Fresno County, 86 in Kings County, 23 in Kern County, and 68 in Imperial County. These tests and other sources of information have indi- cated there are at least four regions in California with different varietal maturity requirements. Southern Sacramento Valley One area of potential production is the Sacramento River Valley from Stockton northward for 50 to 100 miles. Varieties in maturity groups and I have given the best yields here. Chippewa or Chippewa 64 have consistently given the best yields in Yolo County tests. Other varieties satis- factory for this area are Portage and Hark. Two new varieties not extensively tested but having promise are Rampage and Wirth. Central San Joaquin Valley A second potential production area ex- tends from about 50 miles north to about 50 miles south of Fresno. In this area vari- eties in maturity groups II and III are re- quired. Amsoy, Beeson, and Corsoy of Group II maturity plus Calland and Wayne of Group III maturity have pro- duced high yields in tests in Fresno and Kings Counties. Although most of the vari- eties of Group IV maturity have not done well at these locations, one variety, Kent, has been one of the higher yielding vari- eties in these tests. Southern San Joaquin Valley A third area of potential production is roughly 50 miles north to 40 miles south of Bakersfield. Varieties of Groups IV, IVS, or V maturity do best in this area. Calland a variety of Group III maturity did well in one test. Clark 63, Cutler, and Kent have produced the highest yields in limited tests at the USDA Cotton Research Station near Shatter. Hill, Dare and York of Group V maturity have not been tested but would [41] appear to have some promise for this region. Desert areas south of the Tehachapi Mountains The fourth area of potential soybean pro- duction is any farming region south of the Tehachapi Mountains. Varieties of matur- ity Groups VI and VII seem best for this region. Lee, Hood, Pickett and Davis of Group VI maturity have produced the highest average yields in tests in Imperial County. Bragg and Semmes of Group VII maturity have been slightly lower in yield. Frio, a variety adapted for many areas in Arizona has not done well in Imperial Valley tests probably due to the difficulty in obtaining adequate stands. It appears the poor stands are due to salt sensitivity during the germination stage. Cajeme, a new variety grown in Mexico should be tested in this area. Yields Experimental yield tests of soybeans have shown that yields, even from a single variety, may be extremely variable and may range from complete failure to over 3,000 pounds per acre at some locations. Generally, yields of all varieties in any one group under test are either high or low at any one location in any one year. It is not known why there is such extreme variation in yield from year to year or location to location. Higher yields are common in the second season if soybeans follow soybeans on the same field. This is probably due to earlier establishment of an effective symbiotic re- lationship between the bacteria and the plant if the proper Rhizobium are distrib- uted throughout the soil. However, even on fields where well-nodulated soybeans have previously grown it is advisable to inoculate the seed before planting, because the bacteria may not survive from one sea- son to another in our hot dry soils. Representative yields for a few selected varieties in each of the maturity groups are shown on page 43. These and similar data from other varieties have been used to determine varieties that might be ap- propriate for each area of production in California. Yields indicate that on the aver- age about 2,000 pounds of beans per acre could be expected in most areas if the crop is well managed from seedbed preparation through harvest. The varieties that have produced the highest yields in experimen- tal plots are included here as information for those who are considering an experi- mental commercial planting of the crop. Yield data for California have been ob- tained using introduced varieties devel- oped for other specific areas. Usually, vari- ety adaptation to a given environment re- sults in highest yields and thus it seems pos- sible that varieties developed especially for use in California might result in higher yields than those obtained with introduced varieties. However, California cost of pro- duction studies have shown yields approxi- mately double those obtained in past Cali- fornia yield tests would be needed to make soybeans competitive with other crops that can be grown during the same season. An analysis of the situation provides some optimism. California yield tests have shown that soybean production potential here is similar to that of the Midwest. The average yield in Illinois for example is about 2,000 pounds per acre, but a few growers are routinely producing 3.500 to 4,000 pounds per aire and yields in some instances have exceeded 5,000 pounds per acre. This level of production would be profitable on high-priced California irri- gated land if we can establish the combina- tion of cultural practices and germ plasm that will produce such yields here. Varietal adaptation to the California environment would undoubtedly contribute something toward higher yields. The varietal agronomic characteristics that must be improved for profitable pro- duction in California are: higher and more stable yields, a non-shattering pod, and spider mite resistance or tolerance. Other characteristics needing some improvement are: stiff stalks that do not lodge, plants that shed their leaves at maturity, boron tolerance or resistance, salt tolerance or resistance, and better seed quality. A varietal improvement program even with a crop that is widely grown locally rarely can yield an improved variety in less than 10 years of plant breeding effort. Because soybeans need major changes in three important characteristics, and small changes in several other characteristics, it [42 AVERAGE YIELDS (POUNDS PER ACRE) OF THE MOST PROMISING SOYBEAN VARIETIES AT VARIOUS LOCATIONS IN CALIFORNIA FOR YEARS 1967 THROUGH 1969 Varieties Yolo County* Fresno Countyt Kings Countyt Kern County § Imperial County II Group 00 Flambeau Portage 1068 1318 1047 1128 1573 1947 Group I Chippewa 64 Hark A-100 1098 1110 1029H 1181U 1058U 1999H 229311 220111 Group II Am soy Beeson Corsoy 1080 1002 1372 1278 1298 1468 2253 1384** 2132 887 1032 869 Group III Calland Wayne 1344 1273 2660** 1330 2403 1098 Group IV Clark 63 Cutter Kent 1039 1216 1373 1716 1890 2334 1759 1974 1772 Group V Coker 240 Dare Hampton 266 210911 152311 284311 Group VI Davis Hood Lee Pickett 1931 1627 1569 1646 Group VII Bragg Serames 1409 1201 Group VIII Hampton Hardee 1559 1288 * Tests at the University of California Experimental Farm, Davis. Three-year average for 1967, 68, and 69. t Tests at the West Side Field Station, Five Points. Three-year average for 1966, 68, and 69. t Tests at J. G. Boswell Co., Corcoran. Two-year average for 1966-67. § Tests at the Cotton Research Station, Shafter. One-year test, 1968. II Tests at the Southwestern Irrigation Field Station, Brawley. Two-year average 1966-67. II One year only 1966. **One year only, 1967. is unrealistic to believe varieties suitable for California conditions could be de- veloped in less than 10 to 15 years even with adequate funding. The breeding pro- gram should include cultural practices de- signed to maximize yield potential. All present varieties shatter in hot, dry, or windy weather. Rain on dry pods fol- lowed by hot, dry, or windy weather seems to increase the problem. There are varietal differences in the amount of shattering: Clark 63, Lee, and Bragg seem to shatter less than most other varieties and crosses of these and other varieties might increase the level of shatter resistance. Shattering is also known in other soybean production areas, but with higher humidity in these areas the problem is usually less severe. Spider mite tolerance or resistance is an important requirement for successful pro- duction of soybeans in most of California. Although chemical protection is possible, the cost is prohibitive for a low income crop. The screening program described on [43] pages 48 to 50 has identified lines that have spider mite resistance. This resistance, though discovered in the greenhouse, has held up in the field. It may now be pos- sible to develop lines with a usable level of spider mite resistance and other necessary characteristics for a commercial variety. Stiff stems that do not lodge, leaves that fall off at maturity without the need of a frost, and pod development high enough on the stem to be harvested with a com- bine, are necessary for a successful variety. The present varieties are generally suitable but improvement in each characteristic would be desirable, and improved lodging resistance may be essential if 4,000 pounds per acre yields are obtained. \t present diseases are of minor impor- tance in California, but if a large acreage of soybeans were grown here over a period of years, disease would no doubt become more important. Disease resistance would then become an important objective in a varietal improvemeni program. SPIDER MITES AND INSECTS /.. C. Carlson Spider mites Experience over several years has shown that in California the most serious eco- nomic pest of soybeans is the spider mite. Entomological research since 1966 his therefore dealt with control of mites and mite damage. I he species ol spider mites found pri- marily responsible for soybean damage are the two-spotted mite, Tetranychus urticae (K«>ch). and th< Pacini spider mite, T. pad ficus McG. Mites feed b) sucking juices from the plant, mostly from the underside «>! the leaves. 1 he) can build up popula- White spots (stippling) on leaves are caused by moderate infestation by red spider mites. [44] tions of over a thousand mites per leaflet. They cause a white-stippled type of in- jury. With high populations or prolonged feeding the leaves turn yellowish and then brown, and drop prematurely. Defoliation reduces seed yields, significantly, particu- larly if it occurs early. Each female spider mite lays 50 to 60 eggs on the leaves; eggs hatch in about 3 days. The young reach maturity in 10 to 12 days, and in summer the adults live 1 to 2 weeks. Adults hibernate in winter in crevices, trash, weeds, under bark, and in the soil. There are many generations during a year, depending upon climate (principally temperature and humidity), which actually determines the length of each life cycle and the number per season. These mites prefer a dry climate, warm to hot, and build up speedily when the pho- toperiod is long and nutrition is satisfac- tory. They become more severe on plants closely spaced and irrigated infrequently, as this results in greater moisture stress, lower humidity, a decline in plant nitro- gen levels, and higher temperature — all factors favoring spider mites. Dust appears to aid mite development and increase plant damage, although re- search has indicated only that dust may act as a pollutant adding to plant stress. Mite numbers are decreased by many in- sect and mite predators in some areas and on most crops, especially if left untreated by chemicals. These predators generally build up too late to prevent plant damage by the mites, for they do not effectively de- crease mite numbers until late summer or fall. Mites are web-spinning, live in and under their webbing, and migrate to ad- jacent plants and fields via air currents or wind when under population stress. Research has included: (1) an inquiry into the feasibility of controlling mites with chemicals; (2) a correlation of plant damage with mite numbers; and (3) a search for and evaluation of resistant vari- eties. Chemical control of mites. Essentially all this research has been done at the Uni- versity of California at Davis and the West Side Field Station, near Five Points. Plots have been of various dimensions, but rows have always been 30 inches apart. Plants were on raised beds, with irrigations sup- plied in furrows between the beds. Every effort was made to have heavy mite populations in the test area. Varieties Chippewa and Clark, both known to be susceptible, were used. Abundant un- treated soybean material was provided, and on occasion mite-infested leaves were in- troduced into the test areas prior to treat- ments. Spray applications were made with an experimental back-pack sprayer (pressur- ized with COj). The spray was applied at 18.9 gallons per acre at a pressure of 60 pounds per square inch. Granular side dressings were chiseled in 5 to 7 inches from the rows and 5 to 6 inches deep. Mite infestations were measured by tak- ing 20 leaflets at random from each plot and storing them in wide-mouthed pint jars in a refrigerator at 41 °F. Two mite counts were made on each leaflet in areas 1/2 inch in diameter. A 6-inch strap hinge with a drilled l/o-inch hole close to the base of one side of the hinge and another up in the center of the same side was used. Soybean leaflets were then placed, base first, between the halves of the hinge up to the joint. Counts were quickly made of the live mites in each hole or "window" under a binocular microscope at 12 power. Where a single acaracidal spray applica- tion was used, Kelthane® gave the best control of mites (tables 29, 30); two appli- cations of Trithion® gave about the same degree of control. Mite reduction was very good from a 2-pound-per-acre phorate (Thimet®) granular treatment side- dressed into the soil a month after plant- ing (tables 29, 31). Migration of mites from untreated plots in such experiments give data that understate the actual control achieved. Where mite counts were reduced by acaracides at the West Side Field Station in 1966 and 1967, seeds were larger and yield of seed much greater than in un- treated plots (tables 29, 31). At Davis, mite control with Kelthane® and Temik® in- creased yields about 25 per cent in 1966 and 1967 (tables 30, 32). Rank growth of the soybeans and high humidities under the leaf canopy limited mite buildup. In all of these experiments the yield of treated plots would have been much greater in the [45] Table 29 DATA FROM A TEST OF FOLIAGE SPRAY AND GRANULAR SIDE DRESSING USED TO CONTROL MITES ON THE CHIPPEWA VARIETY, WEST SIDE FIELD STATION, FIVE POINTS, 1966° Treatment and number of applications Trithion*, 1 (carbophenothion) Trithion®, 2 ( carbophenothion ) (tetradifon) Kelthane®, 1 (dicofol) Morocide , 1 (binapacryl) (disulfoton) Thimet®, 1 (phorate) No treatment Per cent reduction of live mites t foliage spray (7) (14) (21) (28) 84 76 41 71 84 86 92 81 67 91 86 78 45 55 granular side dressing (9) 16 15 (16] 2 46 (23) 23 89 (30 71 (42) 43 Average number of mites t 10b 5 a 7 a 4 a 19c 26d 8ab 30e Yield' lb. per acre 272b 484a 318b 476a 115c 580 a 58c Weight per 100 seeds § gra 6.5c 7.5bc 6.8c 8.0ab 6.0cd 5.6cd 8.8 a 5.3d 'Sown May 25; foliage sprays applied July 15 and July 26 at 1 lb. active ingredient per acre in 19 gal. H2O/A at 60 psi; side dressing of 10 r i- granular material at 2 lb active ingredient per acre chiseled into the soil 5 inches deep 5 inches from the plants on July 6 and ungated 2 days later. tNumbers in parentheses are days after treatment. tAverage number of mites from all counts during test period. Values are estimates ot the num- ber of mites in an area 1/2 inch in diameter (0.1936 sci. in I. §Values followed by the same letter do not differ significantly. (P 0.05) Duncan's multiple range test. Table: 30 DATA FROM A TEST OF FOLIAGE SPRAYS APPLIED TO CHIPPEWA VARIETY. DAVIS, 1966° Treatment Application ratet Reduction in live-mites and days after treatment Yield* 2 7 1 I 21 Kelthane® (dicofol) Trithion® (carbophenothion) Cygon® 1.0 1.0 0.5 1.5 36 69 67 55 per 77 68 51 38 cent 93 84 71 34 <»2 83 //; per aire 1 ,205a 986b 913b "Sown June 8; sprays applied August 23 at 60 pounds per square inch in 19 gal. H 2 per acre. fActive ingredient in pounds per acre. ^Values followed by the same letter do not differ significantly (P = <0.05) Duncan's multiple range test. absence of migration of mites from un- treated plots. Results in 1968 at Davis showed that treatment with phorate at both planting time and as a seedling side- dressing greatly improved mite control and seed yield from Chippewa. Two acaracidal applications appear to be optimum, and cost 4 to 8 dollars apiece (1972 prices) depending on the material used, the amount needed per acre, and the type and cost of application. Despite good mite control in studies conducted to date, yields have still been low. The pesticides tested are not yet ap- [46] Table 31 DATA FROM A TEST OF FOLIAGE SPRAY AND GRANULAR SIDE DRESSING APPLIED TO GLARK VARIETY, WEST SIDE FIELD STATION, FIVE POINTS, 1967 Treatment Application ratet Percent reduction of live-mi tes£ Number of mites§ II Yiel( Kelthane® (dicofol) GS-19851 Supracide® Morestan® No treatment Thimet® (phorate) Thimet® (phorate) Temik® No treatment (14) 18 (11) 92 83 92 80 foliage sprays (18) 73 73 69 62 granular side dressing (2i: 34 (28) 66 (35) 82 (49) 87 10a 11a 11a 15a 46b 9a 9a 21b 37c //;. per acre 79 275 1 "Sown June 6; foliage sprays applied July 28 at 60 psi in 19 gal. H2O/A; side dressings of 10 per cent granular mater- ial chiseled into the soil 6.5 inches deep and 5 inches from the plants on July 6 and irrigated the following day. fActive ingredients in pounds per acre. ^Numbers in parentheses are days after treatment. ^Average number of mites from all counts during the test period. Values are estimates of the number of mites in a circular area V2 -inch in diameter (0.1936 sq. in.). I IValues followed by the same letter do not differ significantly (P = <0.05) Duncan's multiple range test. Table 32 DATA FROM A TEST OF GRANULAR SIDE DRESSING APPLIED TO TWO SOYBEAN VARIETIES, DAVIS, 1967* Treatment Application ratet Per cent reduction of live mites^ Number of mites§ II Yieldll Thimet® (phorate) Temik® No treatment Thimet® (phorate) Temik® No treatment 14) variety Chippewa (21) (28) variety A-100 (21) (281 87 (35) (35) 6a 4a 38b /a 4a 27b lb. per acre 305bc 446a 249c 312bc 352a 291c "Sown June 12; side dressing of 10 per cent granular material chiseled into the soil 6.5 inches deep, 7 inches from the plants on July 17 and irrigated the following day. fActive ingredient in pounds per acre. ^Numbers in parentheses are days after treatment. §Average number of mites from all counts during the test period. Values are estimates of the number of mites in a circular area '/a -inch in diameter (9.1936 sq. in). 1 1 Values followed by the same letter do not differ significantly (P = <0.05) Duncan's multiple range test. proved or registered for use on soybeans, and cannot be recommended until chem- ical registration and labeling are obtained and federal tolerances and registration are established. Mite numbers versus damage. Compari- sons of mite counts and damage are diffi- cult because of variability in counts from one leaflet to another and from one area to another of the same leaflet. It is also complicated by migration. Nevertheless, these experiments indicate that counts above 5 in a circle i/ 2 inch in diameter will lead to yellowing of the leaf and loss of [47] i r'Ji ' i * -. *'. Severe spider mite damage, foliage loss, and poor pod set are shown in the soybean check plot in the foreground of this photograph. yield. Above a count of 25, leaflets turn The search for mite-resistant varieties. brown and dry up. Untreated plots show Different soybean plants and varieties severe defoliation, and seedpod develop- show obvious differences in tolerance to ment is severely decreased. mites under field conditions. Tolerance Plastic cages 1-inch high and 1-inch in diameter mounted on underside of leaflets. One female was introduced into each cage (see text). [48] appears to be associated in part with stage of development, witli later varieties ap- pearing more tolerant in a nursery with early varieties, but becoming susceptible as they develop further. Even a uniform planting of a single variety will show varia- tions in degree of susceptibility, appar- ently associated with microclimate. Hence, apparent variations in susceptibility under field conditions must be interpreted with great care. Several varieties showing tolerance un- der field conditions were selected for greenhouse tests. A single female two- spotted mite was placed in a small plastic cage mounted on the underside of a soy- bean leaflet. The mites were transferred carefully to the leaflet surface on a one- to-three-bristled camel's-hair brush. The 1-inch plastic cages, cemented to a bent hair clip so they could be clamped tightly to a leaflet, had a soft foam backing to re- duce leaflet injury. The plastic caps were removable for the introduction of mites. A hole drilled in the caps and covered with a very close-meshed cloth provided aeration. There were 10 replications for each variety. Table 33 gives results of a test of 10 varieties. A 2-week mite developmental period proved most effective in measuring varietal differences in resistance. No variety showed complete resistance, but mite development was arrested on varieties P.I. 88,492, P.I. 70,212, P.I. 157,409, and Guelph. Table 34 summarizes results from 14 greenhouse tests. Most of the varieties given a poor rating after 2 weeks are omitted from the table. B-106 (P.I. 88,492) and B-107 (UC-228) were the only varieties showing good to excellent mite tolerance. Both had 81 per cent fewer mites than the susceptible check variety, Chippewa. Varietal field tests in 1968 at Davis veri- fied the tolerance exhibited by B-107. Seed yield was not altered by phorate treat- ment of the tolerant variety B-107 with phorate at planting time and again as a side-dressing in the seedling stage. This is further proof that this variety arrests mite development and damage sufficiently to keep mite numbers below an economic threshold. The 1969 varietal field planting at Davis resulted in excellent plant growth, and the very hot summer promoted high mite de- velopment, especially of the Pacific mite. This species made up about 90 per cent of the mite population present, and differ- ences in damage among varieties were readily apparent. Mite counts (table 35) in- dicated that the varieties B-106 and B-107 reduced mite development the most. A new selection, M-59-213, showed good mite re- duction. There was apparently no corre- lation between seed yield and mite toler- ance among the lines tested. Table 36 shows results from 1969 green- house tests on 10 separate soybean plant- ings. B-106 and B-107 were superior in re- duction of mite development. These two varieties are still the most tolerant to spider mites. The selections UC-1022 and WI4- 221 exhibited fair to good mite tolerance, while CM 1 was good in one test. Table 37 shows results from the 1970 greenhouse tests on seven separate plant- ings of seven soybean selections. These ex- Table 33 AVERAGE NUMBER OF SPIDER MITES ON SEVERAL SOYBEAN VARIETIES, 2 WEEKS AFTER INTRODUCTION OF A SINGLE FEMALE INTO SMALL LEAFLET CAGES, DAVIS, 1967 Variety or plant introduction Number of mites and date female was introduced 5/26/67 6/9/67 6/22/67 P.I. 88,492 P.I. 70,212 11 11 16 27 10 28 19 8 10 5 13 12 11 14 7 11 15 5 9 16 13 Chippewa P.I. 84,976 22 22 P.I. 85,437 22 P.I. 157,409 . . 9 P.I. 80,470 14 P.I. 86,449 ... 21 9 P.I. 68,494 43 [49] Table 34 SOYBEAN VARIETAL DIFFERENCES IN NUMBER OF LINE SPIDER MITES FROM A SINGLE CAGED FEMALE; INCUBATION TIME 2 WEEKS. DAMS. 1968 Number of tests per variety Live adult and nymphal mites per case Variety \verage number Per cent of Chippewaf B-106(P.I. 88.492) B-107 (UC-228) UC-208 Guelph P I 157 409 3 3 1 3 4 4 1 3 2 3 3 3 2 4 14 10 11 12 12 12 13 13 14 14 14 L6 26 J7 19 19 28 30 J 2 UC-219 P I 85 437 J2 2 UC-229 UC-218 UC-3,273 P.I. 70,212 UC-209 UC-220 J5 J6 J 7 39 39 44 Wayne Chippewa 69 LOO "All selections except named varieties were from materials originally supplied !>\ Dr H I Bernard, U S Regional Soybean Laboratory, Urbana. Illinois. fThe largest number of live mites developed on Chippewa, and this variety u.is used is the susceptible check variety. Table 35 SOYBEAN VARIETAL DIFFERENCES IN NUMBER OF LIVE SPIDER MITES AT TWO DIFFERENT DATES IN FIELD EXPERIMEN Is DAVIS 1969 Variety Live adult and nymphal mites"*!" Pei i fni ot ( :hippewa~t Vverage \ ield 8/20 9/9 8 20 9 9 B-106 6a 5 a 6a 6a 8 a 10a 12ab 14ab I4ab 18ab 26b 7a 20 b 24 b 49c 51c 66d 20 J 2 40 47 55 56 69 100 1 1 J 7 74 77 100 ounces pet 100 feet of row 9 ) B-107 M59-213 Hark 10 2 11 6 8 l 12 3 1 I 5 6 7 21 15 B 17 2 6.0 CM 31 C1477 M55-130 Merit Portage Chippewa "Average number of mites from five counts per variety. Values are estimates ot the inn in diameter (0.1936 sq. in). ibei ol mites in an inch fValues followed by the same letter do not differ significantly (P = <0.05> Duncan's multiple range test "|"The largest number of live mites developed on Chippewa, and this variety was used as the susceptible check variety tensive tests confirmed that the selections W-14-221, M-59-213, and CM-1, did indeed give superior reduction in mite develop- ment. The reductions were from 88 to 96 per cent, and along with B-106 and B-107 indicate their potential as breeding ma- terials for future host plant resistance to spider mites. Insects The most damaging insect pest observed on soybeans is the western yellow-striped armyworm, Prodenia praefica Grote. These larvae are primarily foliage feeders, eating such prodigious amounts that plants are sometimes defoliated. Population densities can build up to damaging levels very sud- [50] Table 36 SOYBEAN VARIETAL DIFFERENCES IN NUMBER OF LIVE SPIDER MITES FROM A SINGLE CAGED FEMALE. INCUBATION TIME 2 WEEKS, DAVIS, 1969 Variety Number of tests run Average number of developed nymphs" Per cent of Chippewaf Chippewa B-106 B-107 CM-1. UC-1022 . WI-4-221 . UC-1164 Dae 85 B-48 UC-208 . . UC-1021 B-25 B-23 UC-1244 UC-1498 . 100 15 17 27 28 28 37 58 62 62 65 65 69 77 97 "Average number of mites from all counts during the test period. Values are estimates of the number of mites in a area Vi -inch in diameter (0.1936 sq. in.). fThe largest number of mites developed on Chippewa, and this variety was used as the susceptible check variet; Table 37 SOYBEAN VARIETAL DIFFERENCES IN NUMBER OF LIVE SPIDER MITES FROM A SINGLE CAGED FEMALE; INCUBATION TIME 2 WEEKS, DAVIS, 1970 Nymphs Adults and Nymphs Variety" Average numberf Per cent of Chippewaf Average numberf Per cent of Chippewaf CM-1 B-106 1 2 2 3 3 14 27 4 8 8 12 10 52 100 3 5 5 7 7 23 45 7 12 W-14-221 12 B-107 15 M-59-213 15 U.C.-1022 50 100 "Each variety was tested 7 times at different dates. fAverage number of mites from all counts during the test period. Values are estimates of the number of mites in an area 'A -inch in diameter (0.1936 sq. in.). f The largest number of mites developed on Chippewa, and this variety was used as the susceptible check variety. denly in mid- to late-summer in some local- ities. Chemical control will occasionally be necessary. The salt-marsh caterpillar, Estigmene acrea (Drury) can occasionally cause severe plant damage. It is also a foliage feeder. Other soybean leaf feeders are: the varie- gated cutworm Peridroma saucia (Hiib- ner); the alfalfa looper Autographa cali- fornica Speyer; the alfalfa caterpillar Col- ias eurytheme Boisduval; and the beet armyworm Spodoptera exigua (Hiibner). They have appeared sporadically and have caused minor damage. Western flower thrips, Frankliniella occidentalis (Pergande) have caused dam- age to young seedlings in early summer. However, they do not appear to damage flowers or reduce pod set. Also found on soybean plants, though not in damaging numbers, are the con- sperse stink bug, Euschistus conspersus tinier, other stink bug species, the lygus bug Lygus hesperus Knight, and the dif- ferential grasshopper Melanoplus differ- entialis (Thomas). Aphids have not been observed on soybeans, and the seed-corn maggot has caused no damage. [51 r Western yellow-striped armyworm, Prodenia praefica Grote. ■-■-|li;*;' : '' Salt-marsh caterpillar, Estigeme acrea (Drury). [52] Western flower th rips, Frankliniella occidentalis (Pergande). Lygus bug, Lygus hesperus Knight. Female adult at left, male adult on right. [53] DISEASES D.H.Hall Soybeans are attacked by many organisms that can cause diseases, but diseases that may occur on the crop in California are not known because plantings here are mainly experimental. No limiting disease has appeared in any of the California tests and therefore we can only speculate as to which diseases might become important. The dispersal and survival of the patho- gens involved in diseases in other areas are generally known, as are the environ- mental factors that favor various diseases, and consequently we can list the diseases most likely to attack soybeans in Cali- fornia. Since many soybean pathogens are associated with wet weather, they will probably not be major problems under the arid conditions that prevail for most of the growing season in this state. This section briefly describes the diseases of soybean most likely to be encountered. Revisions can be expected as more experi- ence is gained with the crop. Diseases caused by bacteria There are four bacterial diseases of soy- bean in the U. S., but none is likely to be- come serious in California because lack of rainfall during the growing season is not conducive to spread or infection by these pathogens. These diseases could possibly occur where the crop is irrigated by over- head sprinklers, thus creating an artificial rainfall condition. Two of them, bacterial blight and bacterial pustule, being seed- borne are likely to be introduced into California on contaminated seed. Bacterial blight. Symptoms of bacterial blight, which is incited by Pseudomonas glycinea Coerper appear first as water- soaked angular spots on leaves. The spots turn yellow and then brown as the tissue dies. Several spots may run together, and the dead tissue in the larger spots often drops out. Bacterial pustule. Bacterial pustule caused by Xanthomonas phaseoli (E. F. Sm.) Dows var. sojense (Hedges) Star k Burkh. has similar symptoms, but the spots are yellow- ish-green with reddish-brown centers. Both [ diseases may result in tattered-looking leaves as dead tissue falls out. Diseases caused by fungi Most fungus pathogens that attack aer- ial portions of soybean plants are fa- vored by wet weather and will probably never become established in California. Seed-borne fungi cause brown spot (Sep- toria glycines, Hemmi), downy mildew (Peronospora rnanshurica [Naum] Syd. ex Gaum), and frog-eye leaf spot (Cercospora sojina Hara). These will undoubtedly be introduced into the state but, lack- ing a favorable environment, are not likely to cause concern to growers. Powdery mildew. Powdery mildew is caused by Erysiphe polygoni DC. (More re- cently a second powdery mildew fungus, Mycrosphaera diffusa G. W. Clint 8c Pk., has also been found infecting soybean.) The disease does not appear to be adapted to prolonged survival in the field in the present U.S. soybean-producing areas. Since powdery mildews are common on many crops in California, however, t lie disease could become a serious problem if soybeans are planted extensively. Powdery mildew can be recognized by small colonies of gray-to-white fungus growth on the upper leaf surface. These colonies may coalesce and cover the en- tire surface, giving infected leaves the ap- pearance of being covered with a white powder. Severely affected leaves die and drop from the plant. Phytophthora rot. Phytophthora rot is caused by Phytophthora megasperma Dreschs. var. sojae A. A. Hildeb. Since many Phytophthora root rot diseases oc- cur on other crops in California, this dis- ease could likely become a problem. The fungus can infect the plant at any stage of development. It may cause pre-emer- gence and post-emergence damping-oil, or reduction in vigor, or deatli of plants throughout the growing season similar to Phytophthora root diseases on other crops. The fungus causes a soft watery root rot 54] in the seedling stage, and rapid death fol- lows. On older plants the disease is characterized by yellowing and wilting of leaves, often with brown lesions on the stem. The lesion may extend several inches both above and below the ground. Phytophthora rot is found more often in poorly drained areas of fields and on fine-textured soils. Control requires use of resistant varieties and careful manage- ment to avoid ponding of water or soil water saturation. Pythium rot. Pythium rot will probably occur in California since the causal organ- isms, Pythium ultimum Trow, and P. de- baryanum Hesse., are common in culti- vated soils. These fungi cause seed rot and damping-off of seedlings and may cause root and stem lesions on older plants. P. debaryanum causes stem tissue to appear watersoaked at first but dies rapidly, form- ing long sunken areas that may extend several inches above the soil; wilting and death of the plant follow. The disease is favored by cool, moist conditions. As the fungi that cause the disease are common, there is little that a grower can do to pre- vent the disease on older plants, although an approved seed treatment should pro- vide protection against damping-off. A similar disease occurs on dry beans and blackeyes in California but has never been a major problem on those crops. Rhizoctonia rot. Rhizoctonia solani Kuhn another fungus found in most cultivated soils, is common in California and causes severe disease problems on a number of crop plants. It may cause damping-off of soybean seedlings and a basal rot of stems on older plants. Reddish-brown lesions are formed in the cortical tissues of the below- ground portion of the stem. The lesions often run together and girdle the plant, causing death. Charcoal rot. Charcoal rot is caused by Macrophomina phaseoli (Maub.) Ashley. This fungus is common in California on corn, sorghum, and beans and is found oc- casionally on other crop plants. It attacks its host plants during hot weather, usually following severe water stress. The tissues of roots and stems are invaded by the fungus, which forms small black sclerotia. When the diseased tissue is peeled back, the ex- posed area is grayish-black (hence the name 'charcoal rot'). The disease will most likely be sporadic in occurrence and be associated with irrigating at irregular intervals. Sclerotial (or southern) blight. Sclerotial blight, caused by the fungus Sclerotium rolfsii Sacc, is common to many areas of California and therefore can be expected on soybeans. It is most serious on sugar beets but also attacks many other commer- cial crop plants. During .hot weather the fungus causes a rot, near and below the soil line, that results in death of the plant. The disease resembles charcoal rot in some respects but can be differentiated by the development of fans of white fungus growth on the stem and in the adjacent soil and by the distinctive sclerotia of the fungus. The sclerotia, which are spheres about 1 to 2 mm in diameter, are white at first but become tan to dark brown as they mature. The best control is rotation with non- susceptible crops. Stem rot. Stem rot is caused by Sclerotinia sclerotiorum (Lib.) d By. an organism found in many soils of California. As with the two diseases just mentioned, plant stems are attacked near the soil line. When the rot first appears it is soft and watery: affected tissue is often covered with white cottony growths that soon change to large, black, irregularly shaped sclerotia. Often these bodies may be formed in the stem. This disease is favored by cool, moist weather and is more likely to appear late in the growing season. Diseases caused by viruses Soybean mosaic. Soybean mosaic occurs to some extent in all soybean-producing areas of the United States. Infected plants are stunted, and leaves are a deeper green and narrower than leaves from healthy plants. The leaf margins turn down, and tissue along the main veins is puckered. Symp- toms tend to be masked during hot weath- er. Infected plants have distorted pods, producing fewer seeds than healthy plants and seeds tend to show mottling of color in the seed coat. The virus is spread from plant to plant by several species of aphids. Soybean mo- saic virus is seed-borne, but per cent of [55 transmission varies with the variety (it may be as high as 100 per cent for very suscep- tible varieties). Transmission through the seed makes introduction of the disease into California very probable. Yellow mosaic. The virus causing yellow mosaic of soybean is the yellow bean mo- saic virus, common in dry-bean crops in California. It is transmitted by aphids. Symptoms are a yellow mottling on young- er leaves, developing into necrotic spots as the leaves mature. The disease is seldom a serious problem, even though widely distributed in the Midwest. Bud blight. Bud blight of soybean is caused by the tobacco ringspot virus. Symptoms vary with the stage of plant development. With infection before flowering the grow- ing point turns brown, recurves, and be- comes dry and brittle. Plants are dwarfed and produce very little seed. With infec- tion during flowering, plants produce small undeveloped pods. Plants infected after flowering produce poorly filled pods that have conspicuous blotches. The virus is transmitted to the seed only if it infects before flowering. The tobacco ringspot virus has been found in California but is not common. This virus could be introduced in infected seed, and since the nematode species that transmits the virus is present this disease could conceivably become a problem. HARVEST AND STORAGE /. R. Goss, M. D. Miller, R. T. Edwards Field experiments at Davis and the U.C. West Side Field Station, and recent re- sults obtained by California farmers clearly show that soybeans are easily combine- harvested because mature seeds are of a size and smoothness that make them readily rubbed out of the mature pods and easily separated from dry straw. Im- proper production practices and negli- gent combine-harvester operations can re- sult in soybean field losses as high as 20 to 30 per cent (Bowers, 1967). The nation- al average is about 10 per cent, divided as follows: Source Per cent Shattered 4.0 Left on stems and lodged 2.0 Left on stubble 2.0 Left by machine 2.0 Total loss 10.0 Annual losses of potential income in this way are about 162 pounds of beans per acre, valued on the farm at about $8.60 (1972 prices). Management tools are avail- able to reduce this loss. The following is a summary of Califor- nia soybean-harvesting experience, coupled [ with findings in the V. S. soybean-growing areas. When to harvest As soybeans reach physiological maturity most of the leaves naturally turn yellow and drop to the ground (even without frost) and seed moisture is rapidly lost, decreasing from about 60 per cent to 15 per cent or less in 1 to 2 weeks (Carter and Hartwig, 1963). Atmospheric conditions at the time have a great influence on the rate of water loss. For example, prolonged rain or fog will slow the drying. Seed moisture at harvest. Although soy- beans can be combined when the beans have reached 15 per cent moisture, harvest efficiency is best when seed moisture is down to 12 to 14 per cent. For safe stor- age, beans harvested with higher moisture must be dried down to about 13 per cent or lower by aeration (with atmospheric or heated air). Delaying harvest until mois- ture is 6 to 8 per cent will result in excess- ive pod and seed-shatter losses by the header. When fields have dried excessively, night harvesting helps reduce shatter losses. Chemical maturation. Since soybeans ma- 56] ture in the fall, growers are anxious about possible rain damage and therefore would like to use chemical foliage sprays to speed harvest readiness. Unfortunately, USDA experimental results in the soybean-grow- ing areas have shown that defoliating soy- beans 3 weeks prior to normal yellow leaf drop reduced yield by 30 per cent and speeded the harvest date by only 3 days (Carter and Hartwig, 1963). University of Illinois studies showed that any chemical treatment applied early enough to acceler- ate seed drying appreciably reduced yields. In the soybean-growing areas, the chemical defoliants presently available have been generally most useful in desiccating green weeds in weedy fields to improve havest conditions. Soybean defoliation tests with varieties Chippewa and Hawkeye were conducted at Davis for 2 years, but no materials or methods used hastened harvest readiness to a practical extent. In one experiment a commercially registered defoliant con- taining 40 per cent sodium chlorate and 58 per cent sodium metaborate was ap- plied at 15 pounds per acre as a spray on October 15, when Chippewa had most of its leaves but some pods were ripe, and when Hawkeye had all of its leaves and the pods were green (table 38). The de- foliant did not dry up the Chippewa beans or stems any faster than in untreated con- trols, though it gave some improvement in drying time in the later-maturing Hawk- eye variety. No yield data were collected. In 1957, four desiccating materials were tested on Chippewa soybeans at Davis. The chemical sprays were applied on September 21 to facilitate early-October harvest. All chemicals began to desiccate and defoliate the plants within 7 to 10 days. Several days of heavy rain in the second week of Octo- ber interrupted the experiment. All ma- terials tended to reduce yields, whether desiccating systemically or by contact (table 39). In summary, soybean defoliation with currently available chemicals has the same results in California as in other soybean- growing states. None has been effective in speeding harvest date without reducing yield. Some have been useful in desiccating weeds prior to harvest. Growers planning to try chemical desiccation of weeds should make certain the compound is registered for the purpose, and follow the label in- structions carefully. Direct-combining soybeans For best combine-harvesting, cultural prac- tices should provide: (1) evenly spaced rows 20 to 30 inches apart; (2) 6 to 9 plants per foot of row; (3) level seed beds free of large clods and with gently sloping shoul- ders; (4) soybean plants with pods begin- ning more than 4 inches above the soil; and (5) no green weeds. Once the beans are below 14 per cent moisture, the har- vester operator may have many opportuni- ties to adjust his machine and methods as field conditions change. Causes of combine losses. Harvester losses come from: (1) improper header adjust- ment; (2) improper cylinder adjustment; and (3) separation losses. Most current adapted varieties do not naturally shatter excessively before maturity. A major source of bean loss is a poorly operated header. Cutting too high causes Table 38 EFFECT OF DESICCANT SPRAY ON MOISTURE CONTENT OF SEEDS AND STEMS OF TWO SOYBEAN VARIETIES, DAVIS Days after treatment Per cent moisture Chippewa Hawkeye Date Seed Stems Seed Stems Untreated Treated Untreated Treated Untreated Treated Untreated Treated 10-15 10-20 10-26 11-2 11-11 5 11 18 27 53.1 36.1 25.3 8.3 53.1 35.1 18.1 11.4 72.7 72.9 69.6 68.2 72.7 71.2 71.6 67.9 66.4 55.3 36.6 16.8 66.4 51.9 29.0 11.7 72.1 70.5 70.2 63.2 72.1 71.5 65.5 60.8 [57] Table 39 EFFECTS OF FOUR DEFOLIANT CHEMICALS ON CHIPPEWA SOYBEANS, DAVIS Chemical used Amount of material Harvest readiness dates" Chemical H 2 Oil Yield gallons per acre lb. per acre Dow General® dinotro phenol V* 20 10 10/15 1788 Endothal®t 2 15 — 10/15 1422 Magron® % 15 - 10/17 1764 E-Z Off ®t 2 20 - 10/17 1878 Control - - - 10/20 2016 LSD 05 340 °14 per cent moisture or less. t6.3 per cent by weight of disodium 3.6-endoxohexahydrophthalate. £60 per cent magnesium chlorate hexahydrate + non-boron fire-suppressant. losses from cutting through pods with beans falling to the ground, and from un- harvested pods left in the field on stand- ing stubble. To prevent this, the cutter bar must generally be operated no higher than 3 to 6 inches from the soil surface (using a header height gauge will help reduce losses from this source). When the crop is lodged, pickup guard attachments for the the cutter bar will help recover beans which would otherwise go unharvested. Another source of potential heavy field loss is excessive header-reel speed. When reel speed is too high the dry pods and beans are batted from the plants and lost. Peripheral reel speed should be ad- justed to travel about 25 per cent faster than the forward ground speed of the com- bine. Peripheral speed in feet per minute = 3.1416 times reel shaft speed in revolu- tions per minute times reel diameter in feet. Forward speed in miles per hour (mph) can be converted to forward speed in feet per minute by multiplying mph by 88. The center of the reel should be ad- justed to be about 1 foot ahead of the sickle bar, so that the reel gathers in and brushes the plants toward the combine without batting the beans on to the ground. Although combines operating in soybeans may move forward twice as fast as would be the case if they were harvesting cereals, if the forward move- ment of the combine is too fast the bean plants are pushed forward, with the cutter bar cutting them higher up as they lean forward. Excessive amounts of brans are thus left uncut in the field, and shatter losses are excessive. University of Illinois research has shown that the faster a com- bine travels, the higher it must be set to avoid the risk of running the header into the ground. Tabic 40 shows the results from tests in Illinois (Bowers, 1967). Com- bine cylinder speed and screen and Ian adjustments are important in minimizing broken and ground-up beans and loss of beans out of the rear of the harvester. The Operator's Manual lor the combine will provide useful adjustment guidelines as a starting point. If the peripheral cylinder speed is correct but there are shattered beans in the grain tank, the trouble may be the result of too many beans riding over the clean grain (lower) screen and being cracked as they recirculate through the Table 40 EFFECT OF COMBINE SPEED ON FIELD LOSS OF SOYBEANS UNIVERSITY OF ILLINOIS (BOWERS 1967) Combine speed Stubble height Loss 2.5 .. . mi. per hour in. 6.4 7.3 9.3 lb. per acre 210 282 348 3.2 5.0 58] cylinder. A heavy load of threshed beans in the return can usually be decreased by opening the clean grain screen. If the beans are very dry (below 10 per cent moisture), cylinder speeds should be 1500 feet per minute or less. Improper cleaning of the threshed sample may be due to insufficient air on the shoe screens, overthreshing, weedy con- ditions, or improper engine speed. Cylin- der speed and concaves should be adjusted to rub all of the beans out of the pods with minimum damage to the beans and minimum break-up of the straw. The amount of air on the shoe screens will vary from two-thirds to the maximum possible. The lower screen should norm- ally be 34-inch open, and the top screen 1/9- to ^g-inch open. High loss of thresh- ed beans over the straw walkers or rack is most frequently the result of overload- ing the combine. Harvest experiments. In combine field tests at Davis with variety Chippewa, cyl- inder speeds of 1778 and 1490 feet per minute were tested, with cylinder clear- ance 5/g inch in front and y 8 inch in back. Since only four tests were conducted, no significance is necessarily associated with the fact that two of the three tests con- ducted at a harvest rate of about 2 acres per hour gave a large increase in cutter oar losses. With these machine adjustments used, harvested beans were of planting- seed quality. Recommendations for combine operations Begin harvest operation as soon as pos- sible after the beans in the field average 14 per cent moisture or less. Do not wait until they are less than 10 per cent. To minimize unharvested pods, operate the combine header as close to the soil surface as possible. Use a header-gauge attachment. Header reel peripheral speed should be about 25 per cent greater than forward ground speed of the combine. Harvest slowly for minimum field loss. Presently available chemical desiccants have not proved practical for accelerating bean maturity, but are effective in solving a green weed problem prior to soybean harvest. If used, follow manufacturer's label instructions. Cylinder speeds ranging from 1500 to 1800 feet per minute have given good results in California experiments for low- moisture beans. COMBINE SOYBEAN HARVEST TEST, DAVIS, 1957 Harvester Factor Harvest rate (acres per hour) Cylinder speed (ft. per minute) t Cylinder clearance (front/back, inches) Cutter bar loss (lb. per acre) Clean seed harvested (lb. per acre) Straw walker loss (lb. per acre) Shoe loss (lb. per acre) Total free seed loss (rear combine, lb. per acre) Total unthreshed seed loss (rear combine, lb. per acre) Total harvesting loss (lb. per acre) Total harvesting loss (per cent gross yield) Estimate pre-harvest loss (lb. per acre) Gross yields (lb. per acre) Condition harvested seed: US Grade Mechanical damage (per cent through %i" r. h. screen) Split and broken seed (per cent on %4" r. h. screen) Total mechanical damage (per cent) Test Number* 119 120 121 122 1.0 2.07 2.07 1.93 1778 1778 1490 1490 %-% %-% %-% %-% 45 157 106 46 2825 2525 1568 2500 15 7 9 4 77 68 52 49 10 16 13 13 82 59 48 40 137 232 167 99 4.6 8.4 9.0 3.8 15 14 8 13 2962 2757 1535 2599 2 2 1 1 0.04 0.08 0.07 0.1 3.48 3.17 3.20 3.99 3.52 3.25 3.27 4.09 * Test 119 was in 6-inch drilled rows. Tests 120, 121, and 122 were with 30-inch drilled rows. Lifter guards were used in Tests 119 and 120. Seed moisture at harvest was 10%. t Cylinder speed in ft./min = 3.1416 X cylinder diameter in ft. X rpm. [59] Cylinder concave clearances of "\x inch in front and S/ 8 inch in hack have resulted in a minimum of harvester damage to low- moisture beans. As the harvest days proceed and plants become drier, make combine adjustments to keep bean crackage minimized. II neces- sary, harvest at night. Seed storage. For safe storage after harvest, soybeans should be placed in clean, dry bins or flat storage and maintained no higher than 13 per cent moisture (Holman and Carter, 1952). H beans coming in from tiu- field are mixed with green trash they should be cleaned before being binned. H harvested soybeans hav< more than 1! per cent moisture, the} can be dried l>\ forced ah (atmospheric or heated). Maximum >ii temperature for drying soy- beans should not e\i i ed 11" F, SOYBEANS FOR FORAGE AND GREEN MANURE M. D.Miller, R. '/'. Edwards, M / ll illi Soybeans may be used in California as a summer-grown (top for ha) oi silage pi<> j duction or for green-manure purposes. Good soybean hay has a feeding value about equal to other high qualit) legume hay, although the' coarse stems which make up 10 to 15 per cent ol the soybean hay may be refused by some animals. I he coarse-stem problem can be largeh over- come by using an increased seeding rate, by proper date ol planting, and by well- timed harvesting (Morse and Carter, I Experience in the Midwest has shown that soybeans can be mule into an excel lent silage in combination with corn. There, a combination comprised ol about 2 or 3 parts corn to 1 pan soybeans makes a well-balanced silage thai keeps well and is readily eaten. Because ol the- interest in silage feeding in California, various pos sible crop combinations were tested in both Sacramento and San Joaquin Vallc\ conn ties. Forage varieties. Although varieties grown for bean production may be used, the special forage or "ha\ types" generally yield the best quality forage. These usual- ly have fine stems and small, dark-colored seed. Tests have shown, however, that bean types adapted for California conditions when drilled at 100 to 180 pounds per acre in close drill rows will ecpial the special forage varieties in quantity and quality of forage produced. Time to cut. For hay or silage purposes soybeans ma\ be cut from the time the pods begin to form until the pods begin to mature, bul harvest should begin well Im for< tin Ua\t s begin to fall. I Ia\ mowed at tin t ai I ki stag< w ill have a protein content ol l<» to is per nut. Cui at the latei Stage, the plotnn lontrnt will prob- abh be below 15 pel ( ent . though total ha\ \ kI(I pei acre likeh will be somewhat h ig h ( i I'h(.ium soybean leaves shatter readily wh< n dry, .i\u\ because the sinus dry slow- 1\ i el. ii ive to the leai es, spe< ial hai vest precautions are necessary to produce good quality ha\ . \ good method ol i in ing soybean hay is to h-.i\ c it mi he sw ath for I or 2 days, then lake u into small windrows. II dry- ing conditions are poor, the small wind- rows m.i\ need turning once or twice be- fore baling. Using swathers or mowers equipped with rollei crusher or crimping attachments will hasten the curing or dry- ing process because crushed son bean stems lose moisture more rapidly than intact stems. Hay experiments Forage as well as oil bean variety tests were conducted at Davis and in several counties during l n . r >. r > to 1960. Plantings made in mid-May, 1955, at Davis gave a yield of about 2\<> tons per acre of dry mat- ter containing about 18 per cent protein when harvested in late July or 1 1 weeks af- [60] Table 41 HAY YIELDS AND ANALYSES FROM SOYBEANS SOWN AT TWO DATES, DAVIS, 1955 Date sown Date cut Variety Stage Height (inches) Leaf loss (per cent) Dry matter Protein (per cent) (per cent) (pounds per acre) May 14 May 14 May 14 May 14 July 2 July 2 July 2 July 2 July 2 July 27 July 27 Aug. 10 Aug. 10 Sept. 8 Sept. 8 Sept. 8 Sept. 8 Sept. 8 Harosoy Clark Harosoy Clark Chippewa Harosoy Hawkeye Perry Lee Late bloom Early bloom Early pod Late bloom Early pod Late bloom Late bloom Early bloom Vegetative 44 36 55 46 44 50 48 44 48 5 15 15 15 20 25 15 19.0 17.6 22.1 20.0 18.2 18.2 18.4 15.2 17.4 4910 4750 6690 6820 5120 4900 4970 4760 5050 17.0 18.9 16.0 17.4 18.7 17.8 19.9 19.4 18.9 ter seeding (table 41). Plots harvested at 13 weeks yielded about 3]/ 2 tons per acre, but the protein content had dropped to about 17 per cent. At Hamilton City in Glenn County hay yields of the better varieties were almost 3 tons per acre when harvested about 16 weeks after planting (table 42). When cut about 10 weeks after planting, about 2 1/9 tons of hay per acre were ob- tained at Davis from a planting made July 2. The better varieties sown on June 29 at Hamilton City gave a yield of less than 2 tons per acre when harvested 14 weeks af- ter planting. Varieties did not appear much different in hay yields at Davis, but late maturing varieties were much better at Hamilton City. In 1956 soybean hay experiments, com- parisons included the special soybean for- age varieties Kingwa and Virginia and three yellow-seeded oil-bean varieties. The test at Davis was sown in 6-inch drill rows on May 27, and was harvested on Septem- ber 5. Chippewa yielded 8,625 pounds per acre of dry hay and had 18.3 per cent pro- tein (table 43). The high protein content was a consequence of its mature stage of development. Another forage test was sown at the U.S. Cotton Research Station, Shatter. The same five varieties used at Davis were sown at two dates, May 7 and June 15. Row spacing in these tests was 40 inches. The varieties were harvested when the pods and beans were well developed. All varie- ties had between 14 and 17 per cent pro- tein (table 44). The yield of Kingwa was over 7 tons and for Lee over 8 tons of dry hay per acre. It was noted in this test as well as at Davis that Lee had very coarse stems and was difficult to harvest. Kingwa and Virginia, the forage type soybeans, had fine stems and lodged, but were not difficult to harvest. Similar results have been obtained in other tests at various locations in California in other years. Row spacing, seeding rate and harvest date influence soybean hay yield as well as quality. The protein content of stems, pods and leaves determines the quality of the Table 42 HAY YIELDS FROM SOYBEANS SOWN AT TWO DATES, HAMILTON CITY, 1955 Date sown Date cut Variety Dry matter (pounds per acre) May 9 August 30 August 30 August 30 August 30 August 30 October 8 October 8 October 8 October 8 October 8 Chippewa Blackhawk Lincoln Clark Lee Chippewa Blackhawk Lincoln Clark Lee 4414 May 9 3213 May 9 5880 May 9 5621 May 9 5333 June 29 2113 June 29 1702 June 29 June 29 June 29 2350 4444 3584 [61] Table 43 HAY YIELDS AND ANALYSES FROM SOYBEANS CUT AT DIFFERENT DEVELOPMENTAL STAGES, DAVIS, 1956 (SOWN MAY 27) Dry matter Protein Variety Stage (pounds per acre) (per cent! Chippewa Nearly mature 8625 18.3 Lee Late bloom 8211 16.1 Clark Developed pod 7829 15.2 Kingwa Early pod 7684 11.4 Virginia Early pod 7595 11.1 7989 14 1 'All varieties harvested on September 5. hay. Stems have the lowest protein con- tent (approximately 12 to 14 per cent), leaves have a protein content of 19 to 20 per cent, and the protein content of the pods varies from a low approximating that of the stems to a high of 25 to 27 per cent depending on the stage of devel- opment. As the pods become more mature there is a loss of leaves. The ideal harvest time occurs before there is any appreciable loss of leaves but after the beans and pods have started to mature. Silage experiments In general, soybeans alone are not recom- mended for silage making. This is because the green soybean plants will produce a rather bitter ensilage with a strong, dis- agreeable odor unless the material is wilted to 60 to 65 per cent moisture before being chopped and tightly packed into the silo. The addition of a carbohydrate addi- tive such as chopped corn in the ratio of about 2 or 3 parts corn plant to 1 part soybeans usually will produce a well- balanced silage that keeps well and is readily eaten by livestock (Morse and Car- ter, 1952). The question is in what combi- nation to grow soybeans for ensiling. In a corn and soybeans silage test con- ducted in Tulare County in 1956, we found that soybeans grown alone could not be harvested green with a field chop- per but had to be mowed and dried before chopping. Alternating rows of corn and soybeans grew well, but again there was the difficulty of harvesting soybeans alone. Soybeans planted within the row of corn appeared the most successful method of mixing the two crops for silage; they grew well together and presented no difficulty in harvesting. The seeding rate when in- terplanting should be 14 pounds per acre of corn and 35 pounds per acre of soy- beans. Table 45 gives data from this test. Sudan and soybeans have been used in the Midwest as an ensiling combination, but correct row spacings, seeding rates, and dates of planting must be used to achieve desirable results. An experiment at Davis in 1957 illustrates some of the diffi- culties. On May 22 two varieties of soy- beans (Clark and Kingwa) were seeded in 30-inch rows at 35 pounds per acre. Six- teen days later, Piper Sudan was drilled in 6-inch rows crossways of the soybean rows, using four different seeding rates: Table 44 HAY YIELDS AND ANALYSES FROM SOYBEANS SOWN AT TWO DATES U.S. COTTON RESEARCH STATION, SHAFTER, 1956 Sown May 7 Sown June 15 Date cut Dry matter Protein Date cut Dry matter Protein Lee Kingwa Virginia Clark Sept. 18 Aug. 29 Aug. 29 Aug. 13 lb. per acre 16,120 14,560 9,880 8,840 per cent 14.9 15.4 14.1 15.5 Not harvested Sept. 28 Sept. 28 Sept. 28 lb. per acre 8,320 9,360 9,360 per cent 16.3 15.9 17.3 Average 12,350 15.0 9,013 16.5 [62] Table 45 DATA FROM A CORN-SOYBEAN SILAGE TEST IN TULARE COUNTY, 1956 Treatment Seeding rate Dry matter Corn Soybeans Soybeans alone (variety Lee) 18 12 20 lb. per acre 90 100 20 4,823 9 380 Corn-soybeans interplanted 9,986 10 400 10, 20, 30 and 40 pounds of sudan seed per acre. A month later, the sudan and the soy- beans were nearly equal in height. Before harvest, the sudan at the two higher seed- ing rates almost completely shaded out the soybeans. Sudan at the lower seeding rates did not compete so severely but the soy- beans were weakened and succumbed to spider mites. Effective control of the mites on the soybeans was difficult because of the tall growth of the sudan. This experi- ment shows that local experience with methods of planting this combination is important for good results. Soybeans for green manure Adapted soybean varieties may be used as a summer cover or green manure crop in California. For best results, soybeans should not be allowed to become too ma- ture before being turned under. USDA tests indicate that the highest nitrogen content and approximately the highest yield of green and dry matter are obtained when soybeans are in full bloom (Morse and Carter, 1952). Where a summer grown soybean green manure crop was turned under between each potato crop in a Kern County experiment, the potato market- ability never dropped below 99 per cent in 7 successive crop years, whereas in other treatments there was a highly significant increase in unmarketable scabby potatoes (due to Streptomyces scabies [Oswald et ah, 1956]). The effect on scab of growing soybeans to maturity and turning under the dry straw was not determined. SUMMARY AND CONCLUSIONS B. H. Beard Soybeans, originally introduced into the U.S. from the Orient about the turn of the century is an extremely important crop in many areas. Even though the cattle and poultry industries, and other consumers in California use 600,000 to 700,000 tons of soybeans or soybean products annually at a freight cost of approximately $22 million, the crop has not become established in California. A small acreage of soybeans is grown for hay, silage, forage or as green manure but even for these uses the crop is of minor importance in California. Production costs for soybeans are sim- ilar to other cultivated row crops. Cost estimates vary from $80 to over $100 per acre with our high land values and irriga- tion costs. If the farmer receives 3 1^ to 4i/o cents per pound of beans, a yield of 3,000 to 4,000 pounds per acre is required for a reasonable margin of profit. With this production levef 400,000 to 500,000 acres could be devoted to the crop just to meet California needs. Unfortunately, yields over 2,500 pounds per acre have been rare in California even though many tests have been conducted throughout the state. Growing soybeans as a second crop after harvesting a cereal crop, or after early harvested sugar beets, potatoes, or vege- tables, is a method of reducing production costs by 15 to 25 per cent. Even so it ap- pears that a sustained research program is needed to develop varieties that will give [63] maximum yields under irrigation in a hot dry climate. In California, low relative humidity and soil with a high pH appear to be the environmental conditions that show the most extreme departure from conditions found in soybean production areas. Soybean production does not require any specialized equipment, and a farmer growing other row crops will have the necessary machinery (or it will be avail- able from custom operators). Deep friable soils with good drainage and aeration characteristics, but with high water intake and holding capacity, are ideal for optimum growth. Soil salinity should not be over 5 mmhos per centi- meter, and although small amounts of boron are required either in soil or irriga- tion water anything over 0.5 ppm will cause a necrosis of leaves that can lead to leaf or plant death (depending on con- centration). Soils with less than 40 pounds of phosphorus per acre may require fer- tilization with approximately 50 pounds of P2O5 per acre. Potassium is generally not limiting in California soils, and soy- beans will not require nitrogen fertilizer application if properly nodulated. Soybeans can be planted anytime from early April until July 1st with only minor differences in yield. Seedbed preparation should be similar to that used for other irrigated row crops in the district but double-cropping procedures may be more profitable (as discussed on pages 18 to 20) . Only high-quality seed should be used and seed purchase well in advance will be nec- essary because seed is not regularly avail- able in California. Seeding rates vary with row spacing (55 pounds per acre for 40- inch rows, 65 pounds per acre for 30-inch rows, and 75 pounds per acre for 20-inch rows) but about ten seeds per foot of row, irrespective of row spacing is about right. The seeds should be placed into firm moist soil to about 1 inch and not more than 2 inches below the surface. The soil over the seed should be pressed but not packed around the seed and planters should be designed to leave the surface soil loose over the seed. If high tempera- tures and low humidity prevail during planting time, or if planted as a second crop, an irrigation as soon as possible but not more than 2 or 3 days after sowing will lower soil temperatures and increase the stand. The first time the crop is sown in a field soybean seed should always be inoculated with the soybean type of Rhizobium bac- teria. It is usually advisable to inoculate again if more than a year has passed since the last time soybeans were grown or if the soil was allowed to become completely dry between crops. Inoculation may be done in a farm building or in a shady spot in the field by sprinkling y 4 to 1 pint of water on 60 pounds of seed in a wash tub; the recommended amount of inoculum is then added and stirred by hand until all the seed is almost black with the inoculum. The inoculated seed should be kept in a shady spot and covered with a damp cloth. It is best to place only small amounts of seed in the planter boxes and the inocu- lated seed should be sown immediately. Selection of the proper variety for the location is very important. We have divid- ed California into four areas based on the maturity of the varieties that should be grown. Re sure to get seed of a variety with proper maturity characteristics for the lo- cation. South of the Tehachapi Mountains maturity groups Y. VI and VII should be grown; in southern San Joaquin Valley maturity groups IV or V; in the central San Joaquin Valley maturity groups II and III are best; and in the southern Sacramento Valley maturity groups or I have given the highest yields. Weed control is essential for profitable production of soybeans, and as with other crops a good all-around program is need- ed. A combination of herbicides and culti- vation will probably be required. Consult your Farm Advisor for the latest informa- tion on herbicides that are registered for use on soybeans, and follow directions on the label. Spider mites are always a potential threat to soybean production throughout California. Research has indicated that chemical control is possible but is general- ly too expensive. Some soybean resistance or tolerance to spider mites has been found but has not been incorporated into adapted varieties. Consult your Farm Ad- visor for methods of control for spider mites or insects. [64] Soybean diseases have not been import- ant limiting factors in any experimental planting in California. If large acreages were grown regularly, disease might be- come important. Proper irrigation practices are an im- portant consideration in soybean produc- tion but unless the field has extremely poor drainage the plants will sufler as much from too little water as from too much. Depending on soil characteristics, the crop will require from 20 to 30 inches of water during the growing season. The number of irrigations may vary from two to twelve and will be similar to the needs of other crops grown at the same time. Soybeans should be combine harvested as soon as the beans in the field average 14 per cent moisture. Do not wait because beans will begin to shatter from the pods at less than 8 per cent moisture. Com- bine cylinder speeds should be from 1500 to 1800 feet per minute with concave clearances 5/ 8 inch in front and % inch in the back. The combine header should be kept as close to the ground as possible and the use of a header-gauge attachment is recommended. The header reel speed should be about 25 per cent greater than the forward speed of the combine. Soy- beans must be clean and have 14 per cent or less moisture for proper storage. ACKNOWLEDGMENTS A publication of this kind, which summarizes experiments over a period of years, does not include as authors many people who have helped with various phases of the re- search. We acknowledge contributions made by O. P. Gautom, and Mark Campney, Department of Agronomy and Range Science, Davis; by Terry Braun, Michael Gaffrey, William Kester, and John Campbell, Department of Entomology, Davis; and by Farm Advisors W. G. Lyon and Roy Jeter (Glenn County), W. R. Sallee and R. F. Miller (Tulare County), L. K. Stromberg (Fresno County), O. D. McCutcheon (Kings County), M. D. Morse (Butte County), and Roy Barnes (Kern County). We also ac- knowledge help from Richard Hoover, Fred Fisher, and Richard Munez, West Side Field Station, Five Points; and Richard Reynoso and Mrs. Robert Wagner, Imperial Valley Conservation Research Center, Brawley. Mr. Audie Bell (J. G. Boswell Company, Cor- coran), Dr. W. R. Powell (Kern County Land Company, Bakersfield), and Les Hefferline (Pacific Vegetable Oil, Woodland) helped conduct some of the yield tests, and George Cavanagh and R. E. Pruitt (Ranchers Cotton Oil, Fresno) made oil and protein anal- yses of many yield test samples. Several companies furnished financial assistance to support soybean research from 1955 through 1957. We acknowledge this support with gratitude: Albers Milling Company, Los Angeles J. G. Boswell Company, Corcoran Cargill, Incorporated, San Francisco Kingsburg Cotton Oil Company, Kingsburg Pacific Vegetable Oil Corporation, San Francisco Poultry Producers of Central California, San Francisco Producers Cotton Oil, Fresno West Coast Oilseeds Development Committee, Arizona and California Several companies have furnished chemicals for use in soybean experiments. We here- with thank: The Dow Chemical Company Pennsylvania Salt Mfg. Co. General Chemical Division Niagara Chemical Division Hercules Powder Company Stauffer Chemical Company Chemagro Corporation California Spray Chemical Corp. American Gyanamid Company Rohm and Haas Company [65 From 1966 to the present, soybean research in California has been financed jointly by the University of California, Davis; the U.S. Department of Agriculture, Agricultur- al Research Service, Oilseed and Industrial Crops Research Branch; and the Oil Seed Crops Research Trust. We are especially happy to acknowledge the untiring efforts of Mr. C. R. Rathbone (Ranchers Cotton Oil) as chairman of the Oil Seed Crops Re- search Trust. Other members are: R. A. Aker (Anderson, Clayton and Company) G. B. Brewer (Producers Cotton Oil Company) Russell Giffen (Kingsburg Cotton Oil Company) Mark Raney (Kern County Land Company) George Voll (J. G. Boswell Company) This publication is the result of cooperative investigations of the Plant Science Re- search Division, and the Soil and Water Conservation Research Division, Agricultural Research Service, U.S. Department of Agriculture; and the Department of Agronomy and Range Science, the Department of Entomology, the Agricultural Extension Service, the Department of Agricultural Engineering, the Department of Plant Pathology, the Division of Environmental Studies, Agricultural Field Stations, and the Department of Water Science and Engineering, University of California, Davis, California. The re- search was partially supported by a grant from the Oil Seed Crops Research Trust, Fresno, California, and by the Agricultural Research Service, U.S. Department of Agriculture, Cooperative Agreement No. 12-14-100-9411(34) administered by the Plant Science Research Division, Beltsville, Md. U.S. Regional Soybean Lab. No. 761. LITERATURE CITED Abel, G. H. 1961. Response of soybeans to dates of planting in the Imperial Valley of California. Agron. J. 53:95-98. Abel, G. H., and L. W. Erdman 1964. Response of Lee soybeans to different strains of Rhizobium japonicum \gron J. 56:423-24. Abel, G. H., and A. J. Mackenzie 1964. Salt tolerance of soybean varieties (Glycine max L. Merrill) during germination and later growth. Crop Sci. 4:156-61. Amick, R. J., and J. R. Allison 1968. Production practices used and costs incurred in producing soybeans in the Georgia Coastal Plain. Georgia Ag. Exp. Sta. Res. Bui. 46. 24 pp. Barnes, R. M., and B. B. Burlingame 1967. Soybeans. 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January, USDA, FAS, Washington, D.C. 1971b. World Agricultural Production and Trade Statistical Report. October, USDA, FAS, Washington, D.C. Van Schaik, P. H., and A. H. Probst 1958. Effects of some environmental factors on flower production and reproductive efficiency in soybeans. Agron. J. 50:192-97. Wax, L. M., and J. W. Pf.ndf.lton 1968. EfTects of row spacing on weed control in soybeans. Weed Sci. 16:462-65. Wiggins, J. R. 1939. Influence of space and arrangement on the production of soybean plants. Agron. J. 31:314-21. Williams, L. F. 1950. Structure and genetic characteristics of the soybean. In Soybeans and Soybean Products (K. S. Markley, ed.) New York, N.Y.: Interscience Publishers, Inc. Vol. 1:111-34. To simplify the information, it is sometimes necessary to use trade names of products or equipment. No endorsement of named products is intended nor is criticism implied of similar products not mentioned. I0m-6,'73(Q6211L)VL