UNIVERSITY OF CALIFOBNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA GREEN MANURE CROPS IN SOUTHERN CALIFORNIA BY W. M. MERTZ BULLETIN No. 292 February, 1918 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1918 Benjamin Ide Wheeler, President of the University. EXPERIMENT STATION STAFF HEADS OP DIVISIONS Thomas Forsyth Hunt, Director. Edward J. Wickson, Horticulture (Emeritus). Herbert J. Webber, Director Citrus Experiment Station; Plant Breeding. Hubert E. Van Norman, Vice-Director ; Dairy Management. William A. Setchell, Botany. Myer E. Jaffa, Nutrition. Charles W. Woodworth, Entomology. Ralph E. Smith, Plant Pathology. J. Eliot Coit, Citriculture. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Enology. Warren T. Clarke, Agricultural Extension. John S. Burd, Agricultural Chemistry. Charles B. Lipman, Soil Chemistry and Bacteriology. Clarence M. Haring, Veterinary Science and Bacteriology. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. James T. Barrett, Plant Pathology. Fritz W. Woll, Animal Nutrition. Walter Mulford, Forestry. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. J. B. Davidson, Agricultural Engineering. Elwood Mead, Rural Institutions. H. S. Reed, Plant Physiology. W. L. Howard, Pomology. fFRANK Adams, Irrigation Investigations. C. L. Roadhouse, Dairy Industry. O. J. Kern, Agricultural Education. John E. Dougherty, Poultry Husbandry. S. S. Rogers, Olericulture. R. S. Vaile, Orchard Management. J. G. Moodey, Assistant to the Director. W. M. Mertz, Superintendent of Cultivations. Mrs. D. L. Bunnell, Librarian. t In co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA* By W. M. MERTZ INTRODUCTION In a comparison of factors governing agricultural practice in humid climates and in a semi-arid section as southern California, the two most striking differences are apparent in connection with the moisture content and the organic content of the soil. The develop- ment of successful agriculture under this semi-arid condition depends in large measure upon supplying the deficiencies in water and organic material. In the case of water, the question resolves itself into two factors: first, is there an available source of water; and if so, can it be put upon the land at a cost which the returns from the crop will warrant? The question of maintaining the supply of organic material in the soil after the water has once been applied to the land is the next most vital problem. Agricultural soils of semi-arid regions are notably deficient in organic matter. One of the chief concerns of the farmer is to obtain soil organic matter cheaply in order to main- tain a supply in the soil sufficient for the needs of the crops to be grown. Two methods present themselves : the first, that of incorpo- rating into the soil various animal manures and waste products ; the second, that of plowing under green manures grown in rotation with field crops, or between the rows of orchard trees. Where the supply of organic matter is low, there is usually a corresponding lack of nitrogen. Thus the two problems of increasing the organic matter and increasing the nitrogen content, are closely bound together. The use of animal manures tends to accomplish both of these objects. Complications arise, however, in the way of expense, for only a very small percentage of our farmers are stock- raisers, and many orchardists do not even keep their own work teams. It thus becomes necessary for the orchardist to buy a very large proportion of the animal manures used. Under the increasing de- mand, these manures have advanced in price and are available only in limited quantities. 1 Paper no. 46, University of California, Citrus Experiment Station, River- side, California. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The question naturally arises, cannot legumes be found that would be suitable for green manuring, the use of which would maintain both the organic and nitrogen contents of the soil? For several years attempts were made to use various legumes as green-manure crops, especially in citrus orchards. After quite extensive trials, growers in general adopted two species, spring vetch (Vicia sativa), and Canada peas (Pisum arvense). This practice was based largely upon the fact that the seed of these two plants was obtainable in large quantities at reasonable prices and that both crops gave heavy yields of organic material. Of late years, these legumes have not been giving entire satisfaction and are going out of use in large measure. This state of affairs emphasized the necessity for finding other legumes better adapted to the conditions. Since a tendency was shown to revert to cereals as green-manure crops, it seemed advisable to attempt to verify under local conditions the findings of eastern writers on the relative values of legumes and non-legumes. This publication has three objects : 1. To give the results of a six-year experiment on the relative effects of different green-manure crops, including both legumes and non-legumes. 2. To bring up to date the results of a ten-year experiment with green-manure crops in a citrus orchard. 3. To bring together the experimental and observational data on the subject of green manuring in general. A. WINTER GREEN-MANURE CROPS IN ANNUAL ROTATIONS WITH CERTAIN FIELD CROPS OBJECT OF EXPEEIMENT The objects of this experiment were : 1. To determine the relative value of a number of legumes as measured by their ability to produce consistently heavy yields under fall and winter conditions. 2. To determine the relative value of a number of different legumes and non-legumes as green-manure crops, when measured by their effect on the yields of annual field crops following them. 3. To determine the fertilizing value of legume green manures in comparison with commercial forms of nitrogen when added in con- junction with cereal green manures. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA k O 21 a>73 It CD MJ ST M. <• 2 3 a ° 2 CO ^i CD £5 S| S § a' ^. §1 §'» a "• ' b UNIVERSITY OF CALIFORNIA EXPERIMENT STATION HISTOEY The experiment herein outlined was started at Riverside by the University of California, Citrus Experiment Station. The prelim- inary work was under the direction of J. H. Norton. Since 1912, the work has been under the supervision of the author. A tract of land on the Rubidoux Experimental Farm at Riverside, California, was divided into tenth-acre plots, and so arranged that each plot was irrigated separately. These were numbered consecutively from west to east. The soil is a light Sierra sandy loam, tending to become somewhat heavier on the east side of the block. OUTLINE OF EXPEEIMENT In the execution of this experiment, the tract of land used was divided into seventeen plots, each 20 feet wide by 218 feet long, containing approximately one-tenth of an acre. These were numbered consecutively 1 to 17. The plan of the experiment was to grow differ- ent green-manure crops on these plots during the winter months. During the summer following, certain indicator crops, such as corn and potatoes, were to be grown in solid blocks crossing the plots and serve by their growth and yield to demonstrate the comparative value of the different treatments applied to the plots. The plots indicated by the odd numbers have all had some variety of legume grown on them each winter and turned under as a green manure in the spring. The plots of even numbers have had non- leguminous plants grown and turned under. Certain of these non- legume plots were fertilized with commercial nitrogenous materials during the growth of the indicator crop, thus furnishing some means of comparing the value of nitrogen from the leguminous manure crop with known quantities of nitrogen from commercial fertilizer. The treatment given each plot was as follows : Plot 1. — Common vetch (Vicia sativa). (Fig. 1.) Plot 3. — Bur clover (Medicago hispida denticulate) . Plot 5. — Crimson clover (Trifolium incarnatum) , during the first three years of experiment. This crop failed to germinate in every case, and in the winters of 1913-1914 and 1914-1915, the plot was sown to purple vetch (Vicia atropurpurca) . (Figs. 1 and 3.) Plot 7. — Wild lupine for the first year. This failed to germinate, and beginning with the winter of 1910-1911, the plot has had bitter vetch (Vicia erviUa) grown upon it. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 7 Plot 9. — Canada field peas (Pisum arvense). (Fig. 3.) Plot 11. — Tangier peas (Lathyrits tingitanus). Plot 13. — Soja beans for first year. This proved to be too tender for a winter crop, and beginning with the winter of 1910-1911, bitter clover (Melilotvs indica) has been grown upon this plot. (Figs. 1 and 2.) Plot 15. — Fenugreek (Trigonella Foenum-Oraecum) . Plot 17. — Lentils (Lens esculenta). The plots with even numbers have had growing upon them each year the same non-legume. Different crops have been used during the several years. In the winter 1909-1910, weeds were allowed to grow on these plots. During the winters of 1910-1911, 1911-1912, and 1914-1915, barley was grown, in 1912-1913, alfilaria (Er odium cicutarium), and during the winter of 1913-1914, rye was used. CULTUEE OF WINTER CROPS GROWN AS GREEN MANURES The soil was disked or plowed early in September of each year. The clover seed was then sown broadcast and harrowed into the soil. The other larger-seeded crops were sown broadcast and harrowed into the soil for the crops of 1910, 1911, 1912, and 1913. During the other seasons a grain drill was used. Better stands usually followed drill- ing than broadcasting. As soon after sowing as possible, the land was furrowed out for irrigation. From three to five acre-inches of water was applied at intervals of three to six weeks. In the spring, the crop from typical areas (20 x 20 feet) in each plot, was cut and weighed to determine the tonnage of green tops at time of plowing. The results of these weighings are shown in table II where the average tonnage produced by each green-manure crop is given. The samples were cut at the surface of the soil and immedi- ately weighed. The figures on tonnage represent the entire top growth produced on the plots, as no attempt was made to eliminate the weeds during the growth of the crop or at the time of weighing. The tonnages produced are more uniform than would have been the case had the top growth of the planted crop been weighed alone. Thus the tonnages given may be compared with those obtained under ordinary field conditions where a certain percentage of the crop is made up of the common weeds. In late February or early March, a dressing of raw rock phosphate, 540 pounds per acre, and sulphate of potash, 324 pounds per acre, was uniformly applied over all plots. Following this operation, the 8 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION plots were plowed to a depth of nine to ten inches. This was usually done with a large eighteen-inch moldboard plow equipped with fourteen-inch rolling cutter and heavy weed-chain, which completely buried all of the tops. CULTURE OF SUMMER CROPS GROWN AS INDICATORS OF RELATIVE VALUE OF VARIOUS GREEN MANURES Following the preparation of a good seed-bed, summer field crops were planted. This was usually done during the months of March or April, depending upon variety and season. During the growth of these summer indicator crops, applications of nitrogen were made to the non-legume plots, nos. 2, 6, 10, and 14. The amounts and sources of the nitrogen added are shown in Table I : TABLE 1 Nitrogenous Fertilizers Applied to Plots 2, 6, 10, and 14, in Pounds per Acre Dried blood Nitrate of soda during during seasons seasons of 1910, 1911, of 1914 and 1912, and 1913, 1915, Plot Treatment pounds pounds 2 Non-legurne green manure and 123 lbs. N per acre 810 900 6 Non-legume green manure and 41 lbs. N per acre 270 300 10 Non-legume green manure and 163 lbs. N per acre 1080 1200 14 Non-legume green manure and 82 lbs. N per acre 540 600 The nitrate of soda was divided into two or three applications made during the early development of the indicator crops. With the dried blood the entire amount was applied after plowing under the green-manure crops and then disked into the soil before the planting of the summer crops. During the summers of 1910 and 1911, cabbage, corn, and sugar beets were grown as summer indicator crops. "With each of these three crops the yields were heavy, and those of the check plots were reasonably uniform. Potatoes and corn served as the indicator crops for the season of 1912. Potatoes, corn, and sorghum were used as the indicator crop in 1913. The sorghum followed the potatoes which were harvested early in June. During 1914, corn was used as the summer indicator crop. The results of this year were satisfactory, although the wireworm caused considerable irregularity in the stand. Sudan grass was grown as the indicator crop for 1915. This crop was sown broadcast and two cuttings of hay removed. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA L^** i iar : Fig. 2. — A, Melilotus clover plant (1/10 natural size). Note tendency to root deeply. Its upright branching habit is shown in this cut. B, Partial root system of melilotus clover plant (% natural size). Note large taproot and presence of small nodules on the fibers. 10 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION RESULTS OF EXPERIMENTS YIELDS OF DIFFERENT GREEN-MANURE CROPS Assuming that organic matter is of prime importance in main- taining fertility in California soils, the value of green-manure crops must be judged in part by their ability to produce heavy tonnages under average winter conditions. Table II gives the average yield of green matter produced by the different green manures at the time they were turned under. The tonnages vary from 7.5 to 20 tons, with most of the crops averaging about 12 tons of green tops per acre. The very heavy yield of purple vetch is, however, the average of only two years as compared with a five-year average of the other crops. TABLE II Average Tonnage and Composition of Green Matter Turned Under on Each Lot Plot 1 Green manure ; crop Common vetch Average tonnage of green manures on acre basis 12.0 No. of analysis 25 Percent- age of water 82 Per cent nitrogen in green weight .538 Pounds of nitrogen per ton green tops 10.8 Pounds nitrogen per acre 129.6 2 Non-legume* 10.9 4 82 .281 5.6 61.0 3 Bur clover 12.7 21 84 .637 12.7 161.3 4 Non-legume* 9.0 4 82 .281 5.6 50.4 5 Purple vetcht 20.0 5 81 .569 11.4 228.0 6 Non-legume* 9.7 4 82 .281 5.6 54.3 7 Vetch 12.8 4 82 .518 10.4 133.1 8 Non-legume* 9.2 4 82 .281 5.6 51.5 9 Canada peas 7.5 18 80 .633 12.7 95.2 10 Non-legume* 11.0 4 82 .281 5.6 61.6 11 Tangier peas 13.7 5 88 .494 9.9 135.6 12 Non-legume* 8.7 4 82 .281 5.6 48.7 13 Melilotus indica 13.7 9 80 .556 11.1 152.0 14 Non-legume* 10.5 4 82 .281 5.6 58.8 15 Fenugreek 12.3 12 82 .557 11.1 136.5 16 Non-legume* 8.9 4 82 .281 5.6 49.8 17 Lentils 12.1 7 75 .650 13.0 157.3 Average of nine legume plots 13.0 11 81 .572 11.4 148.2 Average of eight non- legume plots 9.7 4 82 .281 5.6 54.3 * Non-legume tonnages and compositions are averages of barley, rye, and alfilaria. t Purple vetch was grown but two years. X The author is indebted to Professor J. H. Norton and Messrs. H. D. Young and E. E. Thomas for most of the analyses from which the averages contained in this table were computed. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 11 Fig. 3. — A, partial root systems of purple vetch (% natural size). Note the number of lateral fibers and absence of any well defined taproot. B, Partial root system of Canada pea i 1 /^ natural size). Note large size of nodules characteristic of this plant. This is not, however, an indication that more nitrogen is being taken from the air. 12 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION Although no records were made of the percentage of weeds present in the various green manure crops, there were very noticeable differ- ences in this regard. The common vetch was always badly infested with the western pigweed (Chenop odium murale). To a lesser extent this was also true of Vicia ervilia and fenugreek. During the last three years of the experiment, the stand of Tangier peas was poor and thus enabled weeds to get a foothold on Plot II. The common vetch was seriously affected with the green pea aphis during the winters of 1911-12 and 1912-13. Bur clover was slow in its early development and was thus unable to smother out the weeds as satisfactorily as certain others. The fenugreek gave poor results during several winters from causes not understood. It is naturally a smaller growing plant than the others and seemed less able to with- stand adverse temperature and moisture conditions. Lentils gave good yields of green tops during the first two seasons, but later suffered from a root disease. Canada field peas gave good yields and pure stands during the first two years, but later the yields were markedly reduced by aphis injury, poor germination and frost. The newly introduced bitter vetch (Vicia ervilia) gave better stands than the common variety, but was not sufficiently vigorous to smother the weeds. Purple vetch, 2 like the foregoing variety, is a recent intro- duction of the United States Department of Agriculture. This variety gave very heavy yields for the two years tested and seemed able entirely to smother weeds. Melilotus indica gave more uniform results as to stand than any other variety tested. Nothing seemed to affect it materially, its most serious disadvantage being its slow early development. It was more easily handled in the spring because of its upright habit and was not seriously damaged by the tramping necessary in orchard heating. Temperatures as low as 16° F., although checking its development, did not injure it as was the case with all other varieties except bur clover. COMPOSITION" OF DIFFERENT GREEN-MANURE CROPS Table II also gives the average nitrogen content of the crops used as green manures in the experiments which includes several of those most commonly used in southern California. The nitrogen content is based on the green weight of the tops at time of plowing. 2 The author is especially indebted to Professor Roland McKee, Assistant Agrostologist, U. S. D. A., Bureau of Plant Industry, for his active cooperation in furnishing seed of the Tangier pea, purple vetch, and bitter vetch (V. ervilia). GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 13 The percentage of nitrogen shown in these analyses indicates that with the legumes a considerable portion of the nitrogen they contain must have been derived from the air, since on the same soil, from two to three times as much nitrogen had gone into the tissues of the legumes, as was the case with the non-legumes. This is further borne out by the analyses of the soils of the various plots. The soil was sampled during January, 1914, while the crops were still growing, thus representing the soil's condition as to nitrogen before that con- tained in the green crop had been returned to it. The average of Fig. 4. — Showing yields of corn on plots 10, 12, and 13, for the season 1912: 10, barley plowed under and 108 pounds of nitrate of soda added; 12, barley plowed under — no fertilizer; 13, bitter clover (Melilotus indica) plowed under — no fertilizer. fifteen analyses of the legume plots showed a total nitrogen content of .032 per cent, while the average of eight analyses of the non-legume plots shows a content of .027 per cent nitrogen. Since these samples were taken to a depth of two feet, this difference of .005 per cent of nitrogen represented an apparent gain of 400 pounds nitrogen per acre. Table III gives the average yields of the six indicator crops for each plot on the acre basis. The figures in italics are the yields of the unfertilized non-legume plots where the green manure crop was rye or barley. The yield of the four unfertilized non-legume plots 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION are uniformly low when compared with those of the plots where legumes had been turned under or where nitrogenous fertilizer had been applied to the non-legume plots. It is significant, however, that the low yields on the unfertilized non-legume plots are practically equal to the state average for these crops. Table IV gives the percentage of increase in yield of the legume plots, and those receiving nitrogen additions over those where non- legume green manures were used alone. These figures were obtained by comparing the yield of each plot where legumes had been turned Fig. 5. — Showing yields of corn on plots 1, 4, and 5 for the season of 1912: 1, common vetch plowed under — no fertilizer; 4, barley plowed under — no ferti- lizer; 5, purple vetch plowed under — no fertilizer. under, with the yield of the adjacent unfertilized non-legume plot. The increases noted on plots 2, 6, 10, and 14, were obtained by com- paring these plots fertilized with nitrogen with the average of the yields of the two nearest unfertilized non-legume plots. Thus Plot 13, where a green-manure crop of Melilotus indica had been turned under, was compared in yield with that of the unfertilized non-legume Plot 12. The yield of Plot 10, which had non-legumes turned under and nitrogenous fertilizer applied, was compared with the average of the yields on the unfertilized non-legume plots 8 and 12. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 15 Very marked effects are noted in the great majority of the cases where a commercial nitrogenous fertilizer was used in addition to rye or barley green manure (fig. 4). With the exception of Plot 2, the amount of increase was roughly in proportion to the amount of nitrogen added. Where 41 pounds of nitrogen was added, the average increase was 12.8 per cent ; with 82 pounds, 30 per cent increase ; and with 163 pounds, 51 per cent increase. Striking results are, however, noticed on plots where legumes were used as green manures (fig. 5). TABLE III Yields Following Various Soil Treatments in Pounds per Acre Plot Treatment Shelled corn, 5-yr. aver. Potatoes, 2-yr. aver. Cabbage, t 2-yr. aver. Beets, 2-yr. aver. Sorghum hav, 1913 Sudan grass hay.t 1915 1 Common vetch 2,125 10 243 30,640 8,363 2 Non-legume + 123 lbs. N Bur clover 2,046 2,135 11,504 13,671 32,106 34,748 11,580 9,489 16 245 3 11,689 14,079 4 Non-legume (check) 1,693 9,275 10,639 26,878 7,505 13 395 5* Purple vetch Non-legume 4- 41 3091 17470 6 lbs. N 1,929 9 982 11,714 25,048 9,114 16,615 7 Vicia ervilia 2,293 13,874 18,139 36,888 9,516 16,957 8 Non-legume ( check ) 1,550 9,942 10 314 21,476 8,792 13,908 9 Canada peas 2 235 14,600 15,571 35,270 11,231 15,789 10 Non -legume + 163 lbs. N 2,462 13,103 15,108 34,424 12 733 20 320 11 Tangier peas 2,523 13,607 16,405 41,192 12,250 17,841 12 Non-legume (check) 1.617 9 823 7,678 24,687 7,881 15,988 13 Melilotus indica '2,754 15,115 19 835 47,300 11,607 19,038 14 Non-legume + 82 lbs. N 2,395 12,256 13,024 31,388 11,770 20,206 15 Fenugreek 2,652 15,322 13,208 33,567 10,374 19,038 16 Non-legume (check) 1973 9 887 11,865 25,362 9 971 16 359 17 Lentils 2 569 12,268 12,793 38,931 12,224 16,800 Aver. of legume plots 2,486 13,588 15,377 37,317 10,632 17,126 Aver. of non-legume plots fertilized with an aver- age i of 102 lbs. nitrogen 2 208 11,711 13,282 30,741 11,299 18,346 Aver. of unfertilized non- legume plots 1,708 9,732 10,124 24,601 8,537 14,912 * Purple vetch was grown as green-manure crop during the years 1914 and 1915 only. t Cabbage on Plots 1 and 2 was so seriously injured by rabbits that the yields of these plots cannot be taken into consideration in getting the average. t Sudan grass was such a poor stand on Plot 1 that it was thrown out of the experi- ment. 16 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION W>0 CO H 1— 1 ci CI CO 01 CO CM sj 1> HJ CO HH : °°. 01 t^ t> Tjj rH ^ r-i T— 1 -n' IO : iH QO t> 0] 01 h rH rH oo : co OS 01 rH CO Ci •* 00 10 oi o » . . 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Being green and succulent at time of plowing the material' rapidly underwent decom- position, thus performing the functions of so-called "active organic matter," and at the same time liberating large quantities of nitrogen which were temporarily locked up in the tissues of the plant while growing during the winter. Determinations on the nitrogen trans- formations in these plots have been made by McBeth. 3 These activ- ities going on during the seasons of blooming and of setting fruit ma}' be in large part responsible for the heavier yields obtained from Plot U as compared with F. Quality Heavy applications of nitrogenous fertilizers, especially if they be bulky, as in the case of stable manure, have been frequently con- demned because of the belief that they tend to produce coarse fruit of a low commercial grade. During the seasons of 1914 and 1915, the fruit from these plots was carefully graded. The results as given in table VI do not support the theory mentioned above, but on the contrary show as large a percentage of high-grade fruit on Plots F, 0, and U, as on the check, and with lemons a very marked advan- tage is evidenced on and U. This last is largely due to the smaller percentage of lemons that became tree-ripe before reaching full size. The column showing the percentage of tree-ripe lemons on the four plots again points to the general superiority of Plot U as regards quality of fruit. The column devoted to a comparison of the per- centages of the desirable sizes, shows an advantage in the case of Plot U as regards size of fruit, i.e., an increase of 17 per cent of desirable sizes in Navel oranges, and 28 per cent in Valencia oranges. Plot F and do not show marked effects upon size of fruit from their several treatments. Size of Tree Vegetative growth is certainly an indication of vigor and health, and with other factors equal, the larger the tree the larger the crop. Since marked differences existed in the size of the trees in the several plots, a method of getting the size of tree by volume was adopted in s McBeth, I. G., Eelation of transformation and distribution of the soil nitro- gen to the nutrition of citrus trees. Jour, of Agricultural Eesearch, vol. IX, no. 7, pp. 194-195, 1917. 22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 1914. A standard fumigation tent was used and the volume cal- culated by means of the Woglum 4 formula. In the columns on tree sizes, there is shown to be a marked increase in size where fertilizers were applied. Trees of all varieties are much larger on Plots F, 0, and U, than on B, but between F and O, there is no constant difference. Trees on F are slightly larger than those on in the case of oranges and smaller in the case of lemons. This fact again emphasizes the relative uniformity of results obtained on these plots regardless of the difference in the amount of phosphate fertilizer applied. "Mottled Leaf" Since the plots discussed have been on a relatively uniform type of soil and have been handled as uniformly as the experiment per- mitted, it is at least interesting to note the marked differences in the percentage of abnormal mottled leaves as shown in the three right- hand columns of table VI. These figures were obtained by taking the averages of several estimates made by a number of separate investigators during the fall months of the three years mentioned. Trees on Plot U have consistently remained more normal as regards leaf development than on the other plots here considered. At the present writing, B stands as before, giving every evidence of starvation, but not showing any material increase in the percentage of mottled leaves. Plots F and O show some increase in the amount of mottling. This is more pronounced on than on F, as the two plots are more nearly similar in this regard than formerly. Plot U shows quite a tendency toward further increases in mottling this season. This is not especially marked with the lemons and Navel oranges, but is beginning to be pronounced with the Valencias. * Woglum, R. S., Fumigation of citrus trees. U. S. D. A., Bureau of Ento- mology, Bui. 90, Pt. I, p. 28. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 23 C. GENERAL DISCUSSION METHODS OF HANDLING In handling green-manure crops, too little care has usually been taken to insure a good stand. This is probably due to a general lack of knowledge of the real value of such crops. When the bitter clover crop will duplicate in result applications of dried blood, costing $35 per acre, the question of how to insure success with the clover becomes one of considerable importance. TIME OF SEEDING In the citrus grove, it is usually considered wise to plow early; that is, during February or March. A good development of any one of the legumes cannot be expected in less than five months. Thus, it is essential to sow the seed during September or the early part of October. In the case of the annual field crops, such as were grown in this experiment, the green-manure crops can be planted after har- vesting of such crops as corn, beets, Sudan grass, and the like. With late corn and cotton, the seed may be sown with the last cultivation and thus get a much earlier development of the legume than would result from awaiting the removal of the crop before seeding. AMOUNT OF SEED TO SOW The amount of seed to sow will vary with conditions, such as the variety and the actual percentage of the land planted. In young orchards practically all the land can be planted, while in old orchards frequently less than one-half the land is available. Since this per- centage of available land will vary so greatly, it is left to each grower to determine the rate of seedage. Taking all the land into consideration, as in a newly planted orchard, or after annual crops, the following amounts of seed per acre may be recommended : Crop Pounds per acre Melilotus indica and bur clover 20 — 30 Fenugreek 35 — 40 Vetches 70 — 80 Peas 90 — 100 Windsor beans 100 — 200 Lentils 60— 70 Average price in cents per pound 6- — 14 8- — 12 3- — 6 4- — 6 3 — 6 9- — 11 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Methods of Sowing The preparation of the soil is another important matter. The small seeded species, such as bitter clover, demand a good seed-bed to insure germination. The soil should be thoroughly worked up with cultivator, disk-harrow, or plow, following the irrigation preceding the sowing of the seed. With bitter clover, the method that has worked to the best advantage has been to broadcast one-half the seed on the dry soil mulch before furrowing. The soil should then be lightly harrowed to cover the seed. After furrowing, the other half of the seed should be sown broadcast over the furrowed land. The portion of the seed falling in the furrows will be covered by the sifting down of the soil on the sides of the furrow, when the water is first turned in. In this way, a good stand can be obtained in the furrow, and if the land is wet to the surface between the furrows, a good stand should follow over all the land. With vetches and peas and all those plants having relatively large seeds, the most successful method has been to irrigate the land and follow as quickly as possible with a cultivator to establish a loose seed-bed. As soon as this is completed, the seed should be sown with a drill to a depth of from two to three inches. Furrowing should follow the drilling in order that no further working of the land be required after the seed has sprouted. Water Requirements of Manure Crop The question of irrigation is very important. As a general rule, it may be said that with a rainfall of fifteen inches or less, no green- manure crop should be grown if irrigation water is not available. Even in some of the irrigated districts, the supply of water during the fall months is not sufficient to keep both the cover crop and the trees in good growing condition. Under these conditions, the ques- tion of growing a green-manure crop is one of getting more water. However, the great majority of orchards are so situated that during the cool fall and winter months sufficient water is available to keep both crops growing normally. After the cover crop has germinated, it is important to keep as much of the original stand alive as is possible. From the standpoint of the cover crop, light but frequent irrigations are best. However, with many growers, it is impossible to get water more frequently than once every thirty days. Under this condition, in the interior valleys, it is often wise to wait until the latter part of September or the first GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 25 of October to plant, in order to miss the excessive heat so often experienced during September. Since the rains do not usually begin until December, from two to four irrigations of the green- manure crop are ordinarily required. The distance between the furrows is also an important item in the irrigation of these crops. On the lighter soils, the furrows should be made close together, from eighteen to thirty inches apart; while on the heavier types the distance may be greater and yet permit of the surface becoming wet between the furrows. Incorporation or Green Manures with the Soil After having grown the crop, it is all-important to incorporate it properly with the soil, for only by so doing is it possible to get the greatest benefit from its use. Unless the crop is worked into the soil before the rains have ceased, it is highly advisable to turn the crop under deeply. In fact, even when a rain or two follows the turning- under of the crop, only a small part of the plant food can possibly be washed down to the roots, as in this short time only a portion of it can have been broken down and become soluble. That portion of the crop which lies in the cultivated surface soil after the rains have ceased can be of but very little value to the growing crop. With furrow irrigation, it is practically impossible to carry down the soluble fertilizer salts that are in the soil above the level of the water in the bottom of the furrow. 5 Again, the high temperatures and excessive aeration of the culti- vated surface soil are very exhaustive of organic material. The cultivation of the soil at such frequent intervals as is commonly practised does not permit of root development into this surface soil. Thus for a variety of reasons, it seems advisable to turn under manures, whatever be their nature, to a depth somewhat in excess of the depth to which the soil is cultivated (figs. 6 and 7). Thus, if it is necessary to cultivate five or six inches deep in order to conserve water, plowing should be done to a depth of from seven to ten inches, depending upon the character of the soil and amount of surface roots. Experience has apparently shown that the cutting of the last year's surface growth of feeding roots does no serious damage to the tree, at least when quantities of organic material are by this means made available to the new feeders which will very soon occupy the level between the cultivated surface and the bottom of the plow furrow. 5 McBeth, I. G., Eelation of transformation and distribution of soil nitrogen to the nutrition of citrus trees. Jour, of Agricultural Eesearch, vol. IX, no. 7, p. 251, 1917. 26 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION In fact, Plot U, which is shown in table VI to be one of the best plots in the Station orchard, has been consistently plowed ten inches deep each year. A mass of feeding roots have been cnt every year, but within sixty days new feeders have largely taken their place. It is still more significant that the first growth in the spring has been Fig. 6. — A, 18-inch moldboard plow used to turn under heavy green manure crops. Note rolling coulter and weed chain. These permit the plow to cover the material much more completely than would otherwise be possible. B, Showing plow seen in A turning under a green manure crop taller than the horses' backs. Note how completely the tops are buried. The absence of a slick furrow slice or the presence of clods shows this land to be in proper condition for plowing. noticeably larger-leaved and more vigorous than in the other plots. This seems to indicate that the locating of the manures within easy reach of the feeding roots much more than overcomes the losses due to the root pruning at the time of plowing. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 27 In the case of large plantings and a relatively short period for plowing, a disk-harrow may be used advantageously to cut up the green-manure crop and establish a mulch to prevent the drying out of the soil until the plow can finish the work. At times the antici- pated late rains do not materialize. In this case, the land should be irrigated before plowing, since nothing is more exhaustive of time and energy than to attempt to turn under a heavy manure crop after the soil has become dry. In fact, this practice may injure the trees to such an extent as to affect the set of fruit markedly for that season. The cultivations of the soil following the turning-under of a manure crop should be done with a disk or knife harrow in order that the organic material may not be pulled out on the surface again. Usually in from six to eight weeks, the regular cultivators may be used, although in some soils there seems to be advantages in the disk and knife harrows, solely apart from their ability to operate in a soil full of bulky, organic material. INOCULATION OF LEGUMES All legumes have the power of utilizing certain amounts of nitro- gen from the air when their roots are infected with certain species of bacteria. These bacteria form colonies at various points along the roots. The enlargements of the roots to accommodate these colonies are commonly called nodules and are familiar to all who have exam- ined the roots of legumes (vetches, and the like) (figs. 1 and 2). Without the colonies of bacteria on the roots, a legume cannot draw upon the supply of nitrogen in the air. It is thus of vital importance to have the legume roots properly inoculated if they are to be used as green manures to add nitrogen from the air. Without the bacteria on the roots, legumes can add no nitrogen to the soil and are no better than barley or rye in this regard. All of the nine varieties of legumes tested in the experiment just outlined were very well inoculated by organisms native to the soil. In fact, this was the case the first year they were sown on virgin brush land. Artificial inoculations on this soil have shown no appar- ent increase in number of nodules or in vigor of plants. Observations made over several of the southern counties have in most cases shown the same general condition. The natural flora of the land contains a large variety of legumes, which are well inoculated and which seem to carry the necessary varieties of bacteria to suit all of the legume crops tested. 28 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION MINOR ADVANTAGES OF GREEN-MANUKE CROPS The growth of winter green-manure crops may bring about savings totally distinct from those already mentioned. In many sections, the winter rains are spasmodic, coming down at times very heavily. Since many orchards are located on the sloping land of the low foot- hills, such heavy rains are apt to do much damage in washing away the top soil. Green-manure crops growing during the season of heaviest rainfall, give almost complete protection from such losses. r% * fKl.s y.4k%*t£ Fig 7. — Showing the appearance of the land immediately after plowing seen in figure 6. Note the total absence of organic matter on the surface. In fact, many growers would not dare to leave their groves in a clean cultivated condition during the winter for this reason alone. In this sense, the green-manure crop becomes a true cover crop protecting the soil from physical losses. The use of a legume manure crop to increase the nitrogen supply in the soil has already been discussed from the standpoint of the nitrogen additions from the air. There is, however, another factor involved in the maintenance of an ample supply of nitrogen in the root-feeding area of the soil. Nitrogen in the forms available to plants is extremely soluble and thus is very easily carried by water. During nearly every winter, there are one or more very heavy rains GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 29 which with the soil already wet from the irrigations may soak down to depths of ten to twenty feet. This water strikes the surface first and the soluble nitrates, frequently very abundant in the upper three to six inches, go into solution and as further rain falls, that which fell first is gradually pushed downward, still carrying the nitrates taken up along the way. Thus the rains wetting the soil very deeply tend to leach out of the surface soil large quantities of available nitrogen. This loss may be very heavy, as evidenced by work carried on by Dr. I. G. McBeth on the movement of nitrates. A green- manure crop growing during the rainy season takes up a very large proportion of the available nitrogen in the soil, and water passing through a soil on which a vigorous crop is growing, finds little soluble plant food to carry to depths beyond the reach of roots. In the incorporation of the green-manure crop, this stored nitrogen is again added to the soil and is rapidly made available to plants through the decomposition which begins immediately if the soil is moist at the time of plowing. Most of legumes used as green manures are relatively deep-rooting. Roots of Melilotus indica have been found to the depth of eight feet in a citrus orchard (figs. 1 and 2). The annual decay of a multitude of these roots undoubtedly has a marked effect on the capacity of the soil to take up water. Under irrigated conditions, many soils develop irrigation hardpan from the sifting downward of the finer particles of soil, and with constant cultivation, winter and summer, this layer may become so compact that air and water will penetrate it with difficulty. The annual growth of green-manure crops tends to lessen this condition, since cultivation as one of the contributing causes is done away with during six months of each year. The decay of the roots of the crop also lessens the effect of the hardpan left over from the previous years. McBeth, I. G., loc. cit., p. 244. 30 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION SUMMARY A number of legumes gave satisfactory yields when grown as winter green-manure crops. Of these, Melilotus indica is the most promising, both from the standpoint of vigor and available supplies of seed. Extensive use shows it to be well adapted to a great variety of conditions. Purple vetch gave very heavy yields and is more rapid in its early development than the Melilotus indica. It should be largely planted when seed becomes available in sufficient quantities. Bur clover did not give as good yields as Melilotus and is of value mainly in sections and under conditions where its early seeding habit will permit of its reseeding itself. Fenugreek is not well adapted to use in southern California. Spring vetch (Vicia sativa) and Canada peas are of value in certain sections where the green pea aphis is not yet a factor. Legumes were shown to be far superior to non-legumes as green- manure crops when measured by their effect on field crops following. The yield of a number of crops following legume green manures when compared with those following non-legumes showed the follow- ing increases : An average increase with potatoes of 39 per cent ; with corn, 45 per cent ; with cabbage, 44 per cent ; with sugar beets, 43 per cent, and with sorghum and Sudan grass, 25 per cent and 18 per cent respectively. Legumes alone gave as good or better results than non-leguminous green-manure crops plus an annual application of 540 pounds per acre of nitrate of soda. Green-manure crops have had a marked effect on citrus trees. The trees on the plot where legume green manures have been annually turned under are superior in every way to those similarly fertilized, where no leguminous green manure has been used. Green manuring has resulted in a 30 per cent increase in size of tree. The total yields at the age of ten years were 68 per cent greater on the green-manured plot. Not only was more fruit produced, but the proportion of fancy and choice fruit was larger. Green manuring had a marked effect upon the size of the fruit, there being 63 per cent more of the desirable sizes (150s, 176s and 200s) than on the plots not green-manured. The trees where legume green manures had been used were in much better health, as evidenced by the fact that only 3 per cent of the leaves were "mottled" during the seasons of 1912, 1913 and 1914, while on plots similarly fertilized, where legumes had not been used, the average was 13.5 per cent. GREEN MANURE CROPS IN SOUTHERN CALIFORNIA 31 Green manures have additional values in that their growth during the winter months prevents serious washing of the soil during heavy rains. Large amounts of nitrogen are saved from leaching below the limits of roots by growing winter green-manure crops which utilize the excess nitrogen and hold it until spring when they are plowed under. The decay of the roots of the crop tends to make the soil more open to the access of air and water. Green-manure crops should be sown during September or October, if satisfactory yields are expected by February or March. The small-seeded legumes, such as Meliloins indica and bur clover, have given good stands when broadcasted before irrigation. Vetches and other large-seeded legumes gave better results when planted with a drill after irrigation and subsequent cultivation, than when broad- casted before irrigation. Irrigation is usually required to grow satisfactory tonnages of the legume green manure crops. When planted in September or October, from three to six acre-inches of water are required to carry the crop until rains begin. With late sowings, rains may sometimes be de- pended upon to start the crop, but in this case irrigation is usually required to carry the crop to full development in the spring and to enable the crop to be properly incorporated in the soil. Green-manure crops may be expected to give most satisfactory results when plowed under to a depth of from seven to ten inches. They should never be plowed under when the land is dry, as this will result in poor incorporation of the green tops and slow decay. With field crops, moist plowing is an absolute necessity if a proper seed-bed is to be obtained before planting the summer crop. Artificial inoculation is seldom necessary in southern California orchards with the winter-growing legumes in common use. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION REPORTS 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viticultural Report for 1896. 1902. Report of the Agricultural Experiment Station for 1898-1901. 1903. Report of the Agricultural Experiment Station for 1901-03. 1904. Twenty-second Report of the Agricultural Experiment Station for 1903-04. 1914. Report of the College of Agriculture and the Agricultural Experiment Station. 1915. Report of the College of Agriculture and the Agricultural Experiment Station. 1916. Report of the College of Agriculture and the Agricultural Experiment Station. 1917. Report of the College of Agriculture and the Agricultural Experiment Station. BULLETINS No. 230. 241. 242. 246. 248. 250. 251. 253. 255. 257. 261. 262. 263. 264. 265. 266. 267. 268. 270. No. 113. 114. 115. 121. 124. 126. 127. 128. 129. 181. 133. 135. 136. 137. 138. 139. 140. 142. 1 43. 144. 147. 148. 150. 151. 152. 153. 154. 155. Enological Investigations. Vine Pruning in California, Part I. Humus in California Soils. Vine Pruning in California, Part II. The Economic Value of Pacific Coast Kelps. The Loquat. Utilization of the Nitrogen and Organic Matter in Septic and Imhoff Tank Sludges. Deterioration of Lumber. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. The Citricola Scale. New Dosage Tables. Melaxuma of the Walnut, "Juglans regia." Citrus Diseases of Florida and Cuba Compared with Those of California. Size Grades for Ripe Olives. The Calibration of the Leakage Meter. Cottony Rot of Lemons in California. A Spotting of Citrus Fruits Due to the Action of Oil Liberated from the Rind. Experiments with Stocks for Citrus. Growing and Grafting Olive Seedlings. A Comparison of Annual Cropping, Bi- ennial Cropping, and Green Manures on the Yield of Wheat. No. 2 71. Feeding Dairy Calves in California. 2 72. Commercial Fertilizers. 2 73. Preliminary Report on Kearney Vine- yard Experimental Drain. 2 74. The Common Honey Bee as an Agent in Prune Pollination. 275. The Cultivation of Belladonna in Cali fornia. 2 76. The Pomegranate. 277. Sudan Grass. 2 78. Grain Sorghums. 2 79. Irrigation of Rice in California. 280. Irrigation of Alfalfa in the Sacramento Valley. 282. Trials with California Silage Crops for Dairy Cows. 283. The Olive Insects of California. 284. Irrigation of Alfalfa in Imperial Valley. 285. The Milch Goat in California. 286. Commercial Fertilizers. 288. Potash from Tule and the Fertilizer Value of Certain Marsh Plants. 290. The June Drop of Washington Navel Oranges. 291. The Common Honey Bee as an Agent in Prune Pollination. (2nd report.) CIRCULARS Correspondence Courses in Agriculture. Increasing the Duty of Water. Grafting Vinifera Vineyards. Some Things the Prospective Settler Should Know. Alfalfa Silage for Fattening Steers. Spraying for the Grape Leaf Hopper. House Fumigation. Insecticide Formulas. The Control of Citrus Insects. Snravinsr for Control of Walnut Aphis. County Farm Adviser. Official Tests of Dairy Cows. Melilotus Indica. Wood Decay in Orchard Trees. The Silo in California Agriculture. The Generation of Hydrocyanic Acid Gas in Fumigation by Portable Ma- chines. The Practical Application of Improved Methods of Fermentation in Califor- nia Wineries during 1913 and 1914. Practical and Inexpensive Poultry Ap- pliances. Control of Grasshoppers in Imperial Valley. Oidium or Powdery Mildew of the Vine. Tomato Growing in California. "Lungworms." Round Worms in Poultry. Feeding and Management of Hogs. Some Observations on the Bulk Hand- ling of Grain in California. Announcement of the California State Dairy Cow Competition, 1916-18. Irrigation Practice in Crowing Small Fruits in California. Bovine Tuberculosis. No. 156. How to Operate an Incubator. 157. Control of the Pear Scab. 158. Home and Farm Canning. 160. Lettuce Growing in California. 161. Potatoes in California. 162. White Diarrhoea and Coccidiosis of Chicks. 164. Small Fruit Culture in California. 165. Fundamentals of Sugar Beets under California Conditions. 166. The County Farm Bureau. 3 67. Feeding Stuffs of Minor Importance. 168. Spraying for the Control of Wild Morn- ing-Glory within the Fog Belt. 169. The 1918 Grain Crop. 170. Fertilizing California Soils for the 1918 Crop. 172. Wheat Culture. 174. Farm Drainage Methods. 175. Progress Report on the Marketing and Distribution of Milk. 176. Hog Cholera Prevention and the Serum Treatment. 177. Grain Sorghums. 181. Control of the California Ground Squirrel. 182. Extending the Area of Irrigated Wheal in California for 3 918. 3 83. Infectious Abortion in Cows. 184. A Flock of Sheep on the Farm. 185. Beekeeping for the Fruit-Grower and Small Rancher, or Amateur. 186. Poultry on the Farm. 1 87. Utilizing the Sorghums. 188. Lambing Sheds. 190. Agriculture Clubs in California. 193. Pruning the Seedless Grapes.