UNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA IRRIGATION OF RICE IN CALIFORNIA BY RALPH D. ROBERTSON Irrigation Engineer, Irrigation Investigations, Office of Public Roads and Rural Engineering U. S. Department of Agriculture (Based on work done at various periods during the years 1913-1916 in cooperation with the Office of Public Eoads and Eural Engineering, U. S. De- partment of Agriculture, the California State Department of Engineering, the Office of Cereal Investigations of the Bureau of Plant Industry of the IT. S. Department of Agriculture,, and the California State Water Commission.) BULLETIN No. 279 May, 1917 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1917 Benjamin Ide Wheeler, President of the University. EXPERIMENT STATION STAFF HEADS OF 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. Robert H. Loughridge, Soil Chemistry and Physics (Emeritus). 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. *A. V. Stubenrauch, Pomology. Walter Mulford, Forestry. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. Elwood Mead, Rural Institutions. J. B. Davidson, Agricultural Engineering. H. S. Reed, Plant Physiology. D. T. Mason, Forestry. William G. Hummel, Agricultural Education. John E. Dougherty, Poultry Husbandry. S. S. Rogers, Olericulture, f Frank Adams, Irrigation Investigations. H. S. Baird, Dairy Industry. David N. Morgan, Assistant to the Director. Mrs. D. L. Bunnell, Librarian. IRRIGATION INVESTIGATIONS (In cooperation with Office of Public Roads and Rural Engineering, U. S. Depart- ment of Agriculture, and State Engineering Department of California) Frank Adams S. H. Beckett H. A. Wads worth Samuel Fortier, Chief of Irrigation Investigations, Office of Public Roads and Rural Engineering. W. F. McClure, State Engineer of California. * Died February 12, 1917. f In co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture. IRRIGATION OF RICE IN CALIFORNIA By EALPH D. ROBERTSON CONTENTS PAGE Introduction : 254 Water Supply and Its Use 254 Preparation of Land 256 Gates 260 Application of Water 260 Duty of Water 264 Drainage 267 Experiments in Rice Irrigation 268 Summary 270 TABLES Table 1. — Summary of Measurements of Duty of Water for Rice on Eighteen Fields in Sacramento Valley, California, 1916 262 Table 2. — Results of Measurements of the Use of Water on the Adams Rice Field near Biggs, 1914, 1915, and 1916 265 Table 3. — Effect of Irrigation Methods and Treatment on Yields at Biggs Rice Field Station of the Bureau of Plant Industry, U. S. Department of Agriculture, 1914, 1915, and 1916 269 ILLUSTRATIONS Figure 1. — 160-acre Rice Field, Showing Good Arrangement of Supply, Drainage Ditch, and Contour Levees 257 Figure 2. — Making Levee in Rice Field with Tractor and Checker in Sacra- mento Valley, California 258 Figure 3. — Homemade Checker or Levee Ridger as Used in Rice Fields in Sacramento Valley, California 259 Figure 4. — Heavy Drag or Leveller used in Preparing Rice Land for Irri- gation in Sacramento Valley 260 Figure 5. — A Satisfactory Gate for Use in Inside Rice Levees 261 Figure 6. — Rectangular Weir and Water Register used for Measuring Irri- gation Water on Adams Rice Field near Biggs, California 266 Figure 7. — One-fifth Acre Plat on Rice Experiment Station near Biggs, Cali- fornia, on which Submergence was Begun Thirty Days after Emergence of Plants 268 254 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION INTRODUCTION The purpose of this bulletin is to describe the irrigation of rice in California, principally in the Sacramento Valley, where about 95 per cent of the California crop was grown in 1916. Descriptions are presented of the methods of preparing land and of the implements used, together with such data regarding use of water on rice as will cover in general the range of questions that most frequently occur to prospective rice growers in California. In addition to data gathered on rice farms throughout the Sacramento and the San Joaquin val- leys, information is presented that has been gathered at the Biggs rice field station of the Bureau of Plant Industry, U. S. Department of Agriculture, where cooperative irrigation experiments were con- ducted during the years 1914, 1915, and 1916. The introduction of rice into California agriculture has stimulated irrigation development and the main increase in the irrigated area of the Sacramento Valley the past few years has been due to the planting of this crop. Rice in the Sacramento Valley has served a two-fold purpose of utilizing land heretofore not used except for scanty pasture or on which grain growing has been declining through decreased produc- tion, and of providing a means of utilizing the waters of irrigation systems which had been constructed but which had not been fully developed on account of lack of settlers. As is to be expected, the industry has attracted people from Japan, China, and India, where rice is one of the principal crops grown, as well as people from the rice sections of Arkansas, Louisiana, and Texas. In many instances these settlers from other states or foreign countries have introduced some customs or practices common to their old environments, but find in California peculiar soil or climatic conditions that may call for entirely new methods. In view of this, a description of methods found best suited to California should be of value. WATER SUPPLY AND ITS USE Approximately 67,000 acres of rice were irrigated in California in 1916. Of this area about 29,500 acres were irrigated from Sacra- mento River, about 24,000 acres from Feather River, about 9800 acres from other streams, and about 3700 acres with water pumped from wells. The first commercial crop of rice in California was grown in 1912 on 1400 acres, and the area in 1916 was more than twice that planted in 1915. The Sutter-Butte Canal, which takes its supply from Feather River about ten miles above Gridley, served the largest area of rice IRRIGATION OF RICE IN CALIFORNIA 255 in Sacramento Valley in 1916, amounting to 17,000 acres. The West- ern Canal, which heads in Feather River shortly above Sutter-Butte Canal, served 5500 acres. The Sacramento Valley West Side Canal, which derives its supply from Sacramento River, supplied water to 8500 acres in Glenn and Colusa counties. The Yolo Water and Power Canal, diverting from Cache Creek, irrigated about 6000 acres. Other large enterprises, which obtained water by pumping from Sacramento River, were the Moulton Irrigated Land Company, California Land and Rice Products Company, Cheney Slough Irrigation Company, Mallon-Blevins Company, and River Gardens Farms Company. The only canal company in the Sacramento Valley serving water for rice irrigation which has as yet sold water on an acre-foot basis is the Yolo Water and Power Company, which charges $1.50 per acre- foot. The Sutter-Butte Canal Company has furnished water for rice to lands having water rights at an annual charge of $5 per acre. Recent contracts made by this company are on the basis of $7 per acre, with reimbursements to the water user for the construction of ditches and for rights of way, provided water has been used for more than two successive years. The amount of water called for in the Sutter-Butte contracts is at the rate of one cubic foot per second for each 53 y s acres. The Sacramento Valley West Side Canal Com- pany, by authority of the California State Railroad Commission, charged $7 per acre for rice. For this charge the water user was entitled to five acre-feet of water per acre, additional amounts to be charged for at the rate of $1.50 per acre-foot. However, no cases are known in which water used in excess of five acre-feet was charged for. Pumping from wells for rice irrigation in California has been chiefly resorted to in the San Joaquin Valley, but to a limited extent also in the Sacramento Valley. There are many opportunities for this type of development where water can be obtained by low lifts from wells or streams either for the entire season or for a portion of the season in supplementing a gravity supply. Owing to the large water-requirements of rice and the steady demand for water through- out a long season, wells should be thoroughly tested before rice is planted and failures can be avoided by keeping the acreage commen- surate with the water supply. The charge for electric power in the Tulare and Kern sections of the San Joaquin Valley is $42.30 per horsepower per annum and in the Sacramento Valley the usual rate for the smaller plants is approximately two to two and one-half cents per kilowatt hour, depending upon the size of the plant and the character of the contract. Engines burning cheap oil or distillate 256 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION may also be used. Centrifugal pumps, on account of their adapt- ability and ease of operation, are the most common type of pump. Twelve-inch wells are commonly used, and the usual contract price for drilling is $1.50 per foot for the first 100 feet and an increase of fifty cents a foot for each additional fifty feet. A study of reports of the United States Geological Survey will assist those who propose to engage in pumping from wells. 1 PEEPARATION OF LAND Land is prepared for rice in contour checks, the difference in elevation between checks varying from .25 to .30 foot where the slope of the country is from two feet to five feet per mile. Usually a surveyor is employed to lay out the field and the cost of surveying amounts to from twenty-five to fifty cents per acre. One of the most rapid methods of locating the contours, in which no stakes are re- quired, is to have the rodman mark the location by shaking a small amount of lime on the ground from a sack. After a few points have been located on a contour, a plow team connects the points by plow- ing four to six furrows which form the base of the levee. Sometimes the contours or field levees are marked by lath stakes, and to avoid confusion where the contours come close together a good plan is to tie a rag of a certain color on the stakes marking one contour and to use a rag of a different color on another contour. Sharp turns in the levees should be avoided wherever possible. Figure 1 shows a 160-acre rice field prepared for irrigation. The head ditch extends along the north line or upper end of the field and follows part way along the east side. A drainage ditch is pro- vided at the lower end along the south side of the field, and also along the west side. The field is divided into eleven checks, the con- tour interval or difference in elevation between checks being .30 foot. It will be noted that there is a direct inlet and outlet provided for each check and also that several gates are placed in interior levees to admit water from one check to another. This arrangement provides good control of water from the head ditch and also offers advantages in draining the field. In case of a break in the ditch or levees the water may be quickly removed and repairs can also be made in one part of the field without interrupting the service in another. The outside levee is made stronger than the interior or field levees and should have a base of six to eight feet and a height of 1.5 to 2.5 i Ground Water for Irrigation in the Sacramento Valley, California : U. S. Geol. Survey Water-Supply Paper 375a. Ground Water in the San Joaquin Valley, California: U. S. Geol. Survey, Water Supply Paper 398. IRRIGATION OF RICE IN CALIFORNIA 257 feet. There is probably no more satisfactory implement for making a strong levee than the Fresno scraper, because the team in passing back and forth over the freshly moved earth packs it down securely. The interior levees are more commonly made with a checker or ridger drawn by a tractor. Figure 2 shows a checker in use. This imple- ment is provided with a device for raising or lowering the rear end, ttAIN SUPPLY LATER RL Outlet/gates DRAINAGE. DrrCH - Fig. 1. — 160-acre rice field, showing good arrangement of supply, drainage ditch, and contour levees. enabling the operator to regulate the size of the levee. More often a simple home-made implement is used such as is shown in figure 3, the cost of which is about $50. The runners for sides are made of three-inch by twelve-inch plank twenty feet in length and are lined with steel. The front end is made ten feet wide on the bottom and the rear end is three feet wide on the bottom. The sides are made two feet high and are set on a batten of one-fourth to one, the tops sloping 258 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION outward. This implement makes a levee having a base of about five feet and a height when settled of about twelve inches. On fairly even ground a crew of two or three men with a tractor frequently check 150 acres or more per day. Often the work is contracted and a com- mon price paid is $50 per day for the use of the tractor and checker. Sometimes the levees are made with a "V" crowder which is also widely used in making field ditches. Recently a "V" made of steel and reversible has come into use. In most sections no attempt has been made to level or grade the land within a check, the preparation of land consisting mainly in building the supply ditches and constructing the levees. In the Fig. 2. — Making levee in rice field with tractor and checker in Sacramento Valley, California. vicinity of Willows large drags or floats drawn by tractors are used to smooth the surface after the land is plowed (fig. 4). It is doubtful if much leveling of land is justified because in fields where knolls or hummocks have been removed to fill in low places it has been found that in the "fills" the plant develops a rank growth of straw and the heads are not filled, while in the heavily-scraped portions of the field the plant is stunted in growth. On the other hand it must be kept in mind that a uniform depth of water over the field is highly desirable. If the depth of water is not fairly uniform there is a difference in the time of maturity of the rice and the yields are also affected, as shown in the experiments at Biggs reported later in table 3. The amount of work and expense justified in preparing the field must therefore rest largely on the judgment of the grower. IRRIGATION OF RICE IN CALIFORNIA 259 The universal practice has been to harvest within a single check on account of the obstructions offered to the passage of machinery by the present type of field levee. It is possible that as the industry pi o» ro— ELEVATION Fig. 3. — Homemade checker or levee ridger as used in rice fields in Sacramento Valley, California. advances more permanent levees with a base of about ten feet and gentle side slopes will be used. The advantages of broad levees, besides those of ease and cheapness in planting and harvesting, are that the cultivated area is increased and weed growth can be better 260 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION controlled. It can not be expected, however, that the growth of rice on the levees will yield any appreciable amount. GATES Gates are necessary in the canal banks to admit water to the checks and also in the field levees for admitting water from one check to another. The canal structures are of the ordinary type used in irri- gation, but the gates in the field levees are less substantial than those usually employed for alfalfa irrigation. It is important to have the gates sufficiently wide to admit the large heads of water used in the initial floodings. Figure 5 shows a simple form of wooden gate which can be installed for about fifty cents. Where the gate is more than Fig. 4. — Heavy drag or leveller used in preparing rice land for irrigation in Sacramento Valley. four feet wide a center division support is used. Box tubes which are sometimes placed through the levees are not generally satisfactory. The gates should be well tamped and preferably puddled in, at the time of placing them, to prevent leaks. APPLICATION OF WATER The irrigation season is divided into two main periods. In the first period irrigations are given to keep the soil moist, but without having the water stand on the field. In the second period the field is continually submerged. It has been found necessary to irrigate after planting to germinate the seed and to give enough subsequent water- ings to maintain growth until the plant is from four to six inches high. The best time to begin submergence, according to the experiments IRRIGATION OF RICE IN CALIFORNIA 261 at Biggs, is about thirty days after the emergence of the plant above ground. The principal reason for not permitting water to stand on the field during the germination period is the danger of the seed rotting in the ground, especially if weather conditions are unfavor- able and the soil is cold. As a rule, water should not be allowed to remain on the land more than one or two days after the initial flood- Fig. 5. — A satisfactory gate for use in inside rice levees. ings. The use of heads of water varying from two to five cubic feet per second or more facilitates quick watering at this time. During submergence the heads need not be so large. In beginning submergence the water should be gradually raised until an average depth of six inches is attained. Likewise at the close of the submergence period the water should be gradually lowered and not hurriedly removed, a rapid draining having a tendency to weaken the straw. Care should be exercised when draining the fields not to cause injury to lower areas. Much damage has resulted to m Yield of paddy rice, sacks per acre (averaging 100 pounds each) pi oil! |** is* End of Beginning of season .. g ® > e a 5 4>\ season g!fe|^g§|Periodof 00 in © CO © CO' CO m 00 in CM c« S " =e!H *2 ^^ *32 *2 rt 2 — 03 "^CC ,-. 0) r- CD <- 03 f- 33 S£~ §£~ Sfc^ Sfe^- ££_• §k^ Z>~ 5f . a ga^ga ga^ga^ga^gs^g-S-s 08oSc8 08«8«c8p W02C»C/2!Z)CCCOPh P"S a" 3 §•2 12 It 2 * o £ _o So 5 cm a m i-h -CM .rrH I*** 80 S ifc 83fc» ^5 ■ ge o <»► gOQC 2* O o'EH 52; oc 'rSHW o. • a « Ocm. 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CO 3 rt CD co 03 eg 1 ° II tp ^ .2 -D CD ^3 CO • "^ "S 3 « 2 3 3 O ^ co ts co .« CD CO 8 § w o 264 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION crops on lands situated below rice areas by water drained from rice fields at harvest time. In one instance many thousands of dollars worth of beans were destroyed in this way. There has been considerable criticism in the past from millers of California rice, who claimed that the rice was cut before being fully matured. When the heads of the grain are well turned down the water should be cut out of the laterals. At this stage of maturity most of the kernels are beginning to harden. On the heel or lower part of the head the kernels should be in the dough stage. After the water is removed it is usually two weeks before the soil is suf- ficiently dry to permit the use of a binder in harvesting the crop. The experiments at Biggs serve to show the best manner of hand- ling the water on soils in that vicinity, but in sections where the soil contains alkali the usual irrigation programme may have to be modi- fied. On alkali lands near Willows the beneficial effects of applying fresh water and of keeping it circulating through the fields were apparent. Irrigators in that section hope to reclaim the land by fre- quent drainage and the application of fresh water. This method is also used in portions of San Joaquin Valley on alkali soils, but where pumping from wells is resorted to the cost of water is a limiting factor. DUTY OF WATER Measurements were made in 1916 of the water used on eighteen representative rice fields in Sacramento Valley. This work was done in cooperation with the California State Water Commission and the results are summarized in table l. 2 Nine of these fields were located on the west side of Sacramento Valley in the vicinities of Willows, Maxwell, and Princeton, and nine on the east side in the vicinities of Biggs, Richvale, Nelson, and Marysville. Ten different soil types were represented. The investigations showed a wide range in the net amount of water used, varying from 4.27 acre-feet per acre to 14.83 acre-feet per acre. The average depth applied to the eighteen fields was 8.23 feet and the average area served per cubic foot per second for the whole season was forty-seven acres. The difference in use was attributed to numerous factors, the more important of which were the character of the soil and subsoil, preparation of land, depth to water table, proximity of lands to sloughs, and manner of handling water. The heads of water used varied considerably in size, owing to the diversity in the size of the fields, but reduced to an acreage basis were fairly uniform. The average head used per acre on the eighteen fields was .052 cubic foot per second before sub- 2 See also Third Eeport of the State Water Commission of California. IRRIGATION OF RICE IN CALIFORNIA 265 mergence and .034 during submergence. For a forty-acre field this would amount to 2.08 and 1.36 cubic feet per second, respectively. On each of three fields where less than five acre-feet per acre was applied, the soil was a black clay adobe, underlain at shallow depths with a non-continuous hardpan with ground water approximately one foot below the surface. These fields were well prepared and the water was carefully handled, little or no water being wasted. Exces- sive use was found on fields close to sloughs or on land with porous subsoil and with poorly constructed outside levees. On the Adams field included in table 1, measurements were made of the water used in 1914, 1915, and 1916, the data for these years being given in table 2. This field is located about three miles north- west of Biggs and comprises 39.5 acres in the NE %, sec. 34, T. 19 N, R. 2 E. The soil is Stockton clay adobe typical of large areas utilized for rice growing in Butte County. TABLE 2 Results of Measurements of the Use of Water on the Adams Eice Field near Biggs, 1914, 1915, and 1916 60 '1 » 03 (3 u ® ..„ <» 5 « £ u-*=" « +a^5 O -HS W) « u £ efl.o a 5 ® c «4-l O 1< O- bO S 3 U ^ op,* o3 S3 C fe-r cu o^ it 5« O 63 £s ^fl fl»a rC-tf a x^ a a 0) .Sr if t* ft"" 2,5 C3 2 CD £ •0. O c8 1914 April 29 June 12 October 12 6 1.04 3.61 4.65 1915 April 21 June 9 October 1 7 1.37 3.50 4.87 1916 April 13 June 9 September 30 6 1.01 3.26 4.27 Taking the three-year period, the average total depth applied was 4.58 feet and the average length of irrigation season from the time of the first irrigation until water was turned off was 167 days. The field was planted to Wataribune variety, a short-grain rice which comprises the greater part of the acreage of rice in California. Yields of approximately 6000, 4500, and 3900 pounds per acre were obtained in the years 1914, 1915, and 1916, respectively. Especial care was given to this field and the yields were above the average. The amounts of water used on this field probably represent the minimum use under gravity canals in Butte County and show what can be accomplished with careful handling of water on well-prepared land. In connection with the above measurements, records of precipita- tion and evaporation from a free water surface tank were kept by 266 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the Bureau of Plant Industry, U. S. Department of Agriculture, on the Biggs rice field station which adjoins the field. The amounts of rainfall and evaporation in the periods corre- sponding to the irrigation season for the years 1914 to 1916, inclusive, are given below : Year 1914 Precipitation during irrigation season, feet 0.21 Evaporation during irrigation season, feet 2.91 1915 0.36 3.17 1916 0.13 3.48 Fig. 6. — Kectangular weir and water register used for measuring irrigation water on Adams rice field, near Biggs, California. Measurements of the water used were made by means of a stand- ard contracted weir and automatic water register shown in figure 6. Average heads of two to five cubic feet per second were used in the initial floodings, while an average flow of .50 to .75 cubic foot per second was continually run during the period of submergence. It is interesting to compare the irrigation practice and data for rice growing in California with those of the rice sections of Arkansas, Louisiana, and Texas. 3 In those three principal rice-growing states all but 2.5 per cent of the irrigated land in rice is supplied with water by pumping, and wells afford a supply for about one-third of this area. For prairie lands the pumping machinery is generally designed IRRIGATION OF RICE IN CALIFORNIA 267 to provide seven and one-half gallons of water per minute for each acre irrigated, which is equivalent to a flow of one cubic foot per second for sixty acres. For the alluvial lands along the streams ten gallons of water per minute per acre is provided, while thirty-eight to forty gallons per minute per acre is sometimes required if the soil is a loose, sandy loam, with a porous subsoil, and is located near a river. The average length of the irrigation season in the rice sections of Arkansas, Louisiana, and Texas, extending from the time of the first application of water until it is removed to permit harvest, is about eighty-six days. The fact that more water is required to mature rice in California than in the rice sections of the south is ascribed principally to the difference in climate. The nights are much warmer in the southern states than in California and there is less difference in the daily range of temperature. The number of days that water must be used to mature rice in California is, therefore, much greater than in Arkansas, Louisiana, or Texas. The rainfall during the irrigation season in California is practically negligible, while in the southern states it may amount to ten or twenty inches. The evaporation in California is generally over twice that in the south. Fortier reports that measurements have been made of rainfall, evaporation, and the duty of water for irrigating rice on prairie lands of Louisiana, Texas, and Arkansas for eleven years, during which twenty-one measure- ments have been made. 4 The averages of these measurements give 15.74 inches of pumped water applied to the land and 17.16 inches of rainfall, and a loss due to evaporation from flooded rice fields of 15.33 inches. DRAINAGE Facilities for drainage are almost as important as for irrigation. The planting as well as the harvesting depends largely upon the condition of the field, and on heavy clay soils which naturally dry out slowly drainage is a most important feature. Poor drainage results in low places remaining wet and not only delays planting, but also impedes the progress of heavy harvesting machinery. Thorough drainage is the only solution for removing alkali salts and for reliev- ing water-logged lands. In sections where drainage is naturally poor the growing of rice with its heavy application of water tends all the more to increase or intensify the needs of drainage. Any effective means of controlling weeds that now menace the rice industry and conditions that will 3U. S. Dept. Agr., Farmers' Bui. 673. 4 Use of Water in Irrigation, 1 ed., p. 229. 268 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION make possible a rotation of crops must depend largely upon adequate drainage. The people of Richvale, realizing the need of lowering the water table which has risen to within a foot of the surface, recently voted $150,000 for drainage. The formation of drainage district No. 833, including lands west of Biggs and Gridley, is a hopeful sign of meeting the problem in that portion of the valley. The opening up of natural water courses and the construction of a comprehensive drainage system in keeping with the flood control work now being undertaken in the Sacramento Valley is likely to have an important bearing upon the future of the rice industry in California. Fig. 7. — One-fifth acre plat on Eice Experiment Station near Biggs, California, on which submergence was begun thirty days after emergence of plants. EESULTS OF EXPEEIMENTS IN EICE IEEIGATION Experiments in rice irrigation were carried on for the years 1914 to 1916, inclusive, in co-operation with the Bureau of Plant Industry, U. S. Department of Agriculture, on the Biggs rice field station. The objects of the investigations were to determine the effect of varying dates of submergence of land, varying depths of submergence of land, the effect of no continuous submergence, as well as the effects of stagnant and slowly-changing water. Attention was also given to fluctuating the depth of water during submergence to determine the effect on the growth of the plant. The tests were made on %-acre plats (fig. 7) enclosed by well-constructed levees and arranged so that IRRIGATION OF RICE IN CALIFORNIA 269 they could be irrigated and drained separately. The soil is a black clay adobe typical of lands utilized for rice growing in the vicinity of Biggs and Gridley. Results of the experiments are given in table 3. TABLE 3 Effect of Irrigation Methods and Treatment on Yields at Biggs Eice Field Station of the Bureau of Plant Industry, U. S. Department of Agriculture, 1914, 1915, and 1916. Yield per acre, pounds A Irrigation treatment 1914 1915 1916 Average Beginning submergence fifteen days after emergence of plant 4510 3860 3750 4040 Beginning submergence thirty days after emergence of plant 5610 4270 4020 4633 Beginning submergence forty -five days after Beginning submergence sixty days after emergence of plant 5410 4100 3890 4466 Submergence maintained two inches deep .... 5010 4030 3620 4220 Submergence maintained four inches deep 5490 4290 3760 4513 Submergence maintained six inches deep .... 5670 4510 3900 4693 Submergence maintained eight inches deep 5220 4400 3940 4520 Slowly changing water 4790 4210 3460 4153 Stagnant water 4940 3990 3800 4243 No submergence (soil kept moist by fre- quent irrigation) 2440 2480 2100 2340 Fluctuation of depth 5290 4160 3690 4380 Each year the best results were obtained by commencing sub- mergence thirty days after emergence of the plant. In 1914 and 1915 the heaviest yields were secured by maintaining a uniform depth of six inches over the land during submergence, but in 1916 the plat submerged eight inches deep gave the heaviest yield, although the increase in yield only amounted to about 1 per cent over the plat submerged six inches deep. Where no water was held on the land, but the soil was merely kept in a mucky condition, only about one- half of a normal yield was secured and the rice was of poor quality. There was little difference in the yield from the plat which received slowly-changing water and from the plat which had no water removed. No reaction on the growth of the plant was shown from fluctuating the depth. In this experiment a uniform depth of four inches was maintained until "booting" was noticeable. Then the water was lowered to a depth of one and one-half inches. The water was held at this depth until the first heads appeared, when it was applied to a depth of four inches and maintained there until the rice was ready to be drained. This scheme is said to hasten the maturity of the rice in the southern states, but apparently has no appreciable effect here. 270 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION In order to determine the maximum and minimum temperatures of water at the various depths of submergence, records were taken daily at 8 a.m., 1 p.m., and 5 p.m. The readings for the shallow depths of water showed higher temperatures during the day and lower temperatures during the night than for the greater depths of sub- mergence. The most uniform temperature was obtained on the plat submerged six inches deep. It is probable the yields are affected to a considerable extent by the daily range of temperature. SUMMARY Approximately 67,000 acres of rice were irrigated in California in 1916, the water supply being obtained principally from Sacramento and Feather rivers. Only about 3700 acres were irrigated by pump- ing from wells. Land is prepared for irrigation in contour checks, preparation consisting mainly in making ditches and levees and installing gates. The gates must be wide enough to admit the large heads of water used in the initial floodings. The irrigation season consists of two periods. Frequent light irrigations with relatively large heads of water are given to germinate the seed and to maintain growth until the plant is four to six inches high, and thereafter the land is continually submerged to a depth of six to eight inches until the rice is matured. Measurements of the use of water in 1916 on eighteen typical fields in Sacramento Valley showed a range of from 4.27 to 14.83 acre-feet per acre, an average depth applied of 8.23 feet, and an average of forty-seven acres served per cubic foot per second. The heads of water used per acre averaged .052 cubic foot per second before sub- mergence and .034 during submergence. The lowest use was on fields with heavy retentive soil, where the preparation was good and the water carefully handled. The average annual use over a three-year period on a field near Biggs was 4.60 acre-feet per acre. During the three irrigation seasons the average precipitation was 0.23 foot and evaporation 3.19 feet. Irrigation practice and requirements in California differ from those in the Gulf states, due mainly to different climatic conditions. Adequate drainage is essential to successful rice production. Planting and harvesting are both delayed while the soil remains wet, and the removal of alkali salts and the relief of water-logged lands are dependent upon drainage facilities. The results of experiments made in 1914 to 1916, inclusive, on black clay adobe soil near Biggs indicated that thirty days after emergence of the plant is the best time for commencing submergence, and that six inches is probably the most advantageous depth of sub- mergence. Very poor yields were secured where no water was held on the land. Fluctuating the depth of water had very little effect on plant growth. More uniform temperatures of the water were found with the greater depths of submergence.