UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA IRRIGATION INVESTIGATIONS WITH FIELD CROPS AT DAVIS, AND AT DELHI, CALIFORNIA 1909-1925 S. H. BECKETT AND M. R. HUBERTY (Based on data gathered in cooperation with the Division of Agricultural Engineer- ing, Bureau of Public Roads, U. S. Department of Agriculture, and the Division of Engineering and Irrigation, California State Department of Public Works.) BULLETIN 450 March, 1928 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA 1928 IRRIGATION INVESTIGATIONS WITH FIELD CROPS AT DAVIS, AND AT DELHI, CALIFORNIA, 1909-1925 1 S. H. BECKETT2 and MAETIN E. HUBEETY3 This bulletin reports the results of certain irrigation experiments with field crops in the Sacramento and San Joaquin valleys. The work, as originally planned, was limited to the irrigation tract of the University Farm, at Davis, the purpose being to determine the duty of water for alfalfa and field crops and the methods of applying the water to obtain maximum returns. In 1922, as a part of the coopera- tive investigations, alfalfa studies were also undertaken on the irri- gation experimental tract at Delhi, in the San Joaquin Valley. INVESTIGATIONS WITH ALFALFA AT THE UNIVERSITY FARM AND AT DELHI In 1907, a tract of twenty-five acres was set aside. Experiments were started in 1909. The planting of experimental orchards and vineyards on the tract in 1915 and 1917 necessitated a rearrangement of the fields, making it impossible to maintain a uniform system of plot numbering throughout the sixteen years covered. Figures 1 and 2 show the general arrangement of plots during the periods 1911-1915 and 1915-1925. The soil of the tract is described as a Yolo fine sandy loam of medium texture to a, depth of 18 to 20 feet, having a maximum soil moisture 'field capacity ' of 20 to 22 per cent. At no time during the investigations was the underground water table closer than 14 feet from the surface. From time to time, attempts were made to obtain information on the use of water by means of intensive soil sampling. Variability of the soil made it impossible, however, to secure reliable results by that method. The experiments were limited, therefore, to a study of yields under different irrigation treatments. i Eesults of the investigations have been, in part, previously published in U. S. Department of Agriculture Bulletin 10, California State Department of Engineering Bulletin 3, California Agricultural Experiment Station Bulletin 280, and biennial reports of the State Engineer of California and the Director of the California Agricultural Experiment Station. The work at Davis reported herein has been conducted by the authors; that at Delhi mainly by Martin E. Huberty and Frank Davis, Junior Irrigation Engineer, Division of Irrigation Investigations and Practice. 2 Associate Professor of Irrigation Investigations and Practice and Associate Irrigation Engineer in the Experiment Station. 3 Assistant Irrigation Engineer in the Experiment Station. 4 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The water supply was obtained by pumping, a storage reservoir of one-quarter acre-foot capacity being used to regulate the flow. Delivery of water from the pump and the reservoir to the various field ditches and plots was made through a concrete pipe system. All water used in the experiments was measured by means either of rectangular weirs located in weir boxes in the pipe lines, or by temporary weirs installed in the field laterals. GOAD Fig. 1. — Experimental irrigation tract, University Farm, Davis, California, showing areas included in investigations, 1912-1915. Standard practices for the localities were followed in the prepara- tion of land for irrigation, in the preparation of seed bed, and in irrigation, cultivation, and harvesting. The time to irrigate was deter- mined by examination of the moisture condition of the soil and by the appearance of the crop, an attempt being made to secure maximum yields under the various treatments. In 1920, a tract of forty acres was leased from the State Land Settlement Board at Delhi, California, to be used in cooperative irri- BUL. 450] IRRIGATION INVESTIGATIONS WITH FIELD CROPS 5 gation investigations. The soil of the tract is described as an Oakley fine sand, ranging in depth from 6 to 9 feet. The maximum 'field capacity' ranges from 6 per cent at the surface to 10 per cent and 12 per cent at the lower depths. A tough calcareous hardpan, light gray in color, 10 to 12 inches in thickness and practically impervious to water, underlies the whole area at depths of 6 to 9 feet. /?OAD vN FIELD 1 7.9 AC PES /9I6 3EAHS /917'BO ALFALFA /9EI -as F/ELD CPOPS O/PCHAPD 3.46 ACPES f/eld a 4.43 ACRES /9l6-'/9 F/ELO CtfOPS /9aO-£5 ALFALFA F/ELD 4 /.a AC PES /9/6- 'as ALFALFA OPCHARD V/NFYA&D F/ELD S /. 7S ACPES 19/6 -'SI CPA/N /9aa-'a5 alfalfa r ^ X — 7^ ^cr^-^. \U PUMP MOUSE Fig. 2. — Experimental irrigation tract, University Farm, Davis, California, showing areas included in investigations, 1916-1925. Water for irrigation was obtained by pumping, distribution being made to the entire area through a concrete pipe system. Water applied was measured by rectangular weirs placed in the distributing system. Figure 3 shows the arrangement of the plots with the irrigation schedule followed from 1922 to 1925. The land was prepared for irrigation in the winter of 1920 and seeded to alfalfa in the spring of 1921. During 1921, there was no variation in irrigation treatment, sufficient water being applied during the season to produce normal growth. UNIVERSITY OF CALIFORNIA EXPERIMENT STATION <*SD'- k \ k K 10 J /VOT- //V EXPEP/MENT K II TWELVES-INCH//?/?. 5 /j /v//vf / /y^r IN EXPERIMENT 3~ TWELVE 3 -INCH IRRIGATIONS 7 /VINE II THREE 12 IS IB ffl A3 /y^r /// EXPERIMENT ^ Af 77*RfiT 4-IHCH IRRIGATIONS vj /<9 7 i *, J2 13 24 JO 36 48 DEPTH OF I RR I GAT/ON IN INCHES 60 Fig. 4. — Diagram showing results of alfalfa duty-of-water experiments at University Farm, Davis, 1910-1915. Note the maximum yield with an annual application of 36 inches of water. Under the conditions present, the most economical yields were obtained with annual applications of 30 to 36 inches. TABLE 7 Boot Distribution of Alfalfa under Variable Irrigation Treatments at Delhi Depths, inches Six 8-inch irriga- tions, 1922-25 Six 6-inch irriga- tions, 1922-25 Three 4-inch irrigations, 1922-24; six 6-inch irriga- tions, 1925 Twelve 3-inch irrigations, 1922-24; four 6-inch irriga- tions, 1925 Dry wt., grams Per cent of total Dry wt., grams Per cent of total Dry wt., grams Per cent of total Dry wt., grams Per cent of total 305.8 396.4 201.7 135.9 103.4 62.8 44.3 29.1 18.3 12 1 8.8 Hard pan 371.4 451.7 228.3 140.0 112.6 89.7 66.7 41.1 38.7 18.4 15.5 es 8.7 5.8 418.6 486.9 220.3 178.1 125.2 84.6 72.0 47.9 35.4 24.4 22.7 16.4 13.8 384.2 511.9 276.6 164.0 128.8 84.6 '82.0 52.4 38.5 32.6 26.4 14.2 Hard pan a 0- 6 39.1 19.9 13.4 10.3 6.2 4 4 2.9 1.8 1.2 .8 at 60 inch 37.0 18.8 11 5 9.2 7.4 5.5 3.4 3.2 1.5 1.3 0.7 5 36.8 16.6 13.4 9.4 6.4 5 4 3.6 2.7 1.8 1.7 1.2 1.0 36.2 6-12 19.6 12-18 11.6 18-24 9.2 24-30 6.0 30-36 5.8 36-42 3.7 42-48 2.7 48-54 2.3 54-60 1.9 60-66 1.0 66-72 1 63 inches IU r 1 ■ 1 1 1 ■ 1 ■ J i { { l£ 18 24- 30 36 AZ A6 DEPTH OF I RR 1 6 AT/OH //V INCHES 60 Fig. 5. — Diagram showing results of alfalfa duty-of -water experiments at Delhi, California, 1922-1924. Note the maximum yields with an annual appli- cation of 42 inches of water. Under the conditions present, the most economical yields were obtained with annual applications of 36 to 42 inches. 12 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 6 12 id 24 !-» &4S J* 66 66 72 Irriqofion^ per reason Twelve 2i inch Per cent Roots Jo// type Eight j£ inch Per cent Roots So/7 type Fe-r cent Roots So/i type 33. IJ^Aa^H Sonde/ Loom '*'"' 3 ■ ^Jdndo Loom ^^ ■ ^Sjnct/ Loom iA.e $g£ i5.z B3B 15.9 ||k 11.9 #^ /^./ ip //2<5 Si- 6.5 9 6"./ £ " de? „ r *, 1 S3 >> ti 6.P ,. 6: j fi 4.8 [ ,, M A. 6 „ , *» t) AA J > ♦ ap ., 2.3 Fine Sandy Loom » 2.5 Fine Sand 2.6 „ , 2.7 /7/7(? Sandy Loam & F/ne Sand 2.2 » »> 2.3 >> » 2A „ 1.8 >J M 1.3 » » 1.6 fv/re Sand f.S Grave/ 1.7 /va^ Sandy Loam and Grave/ 6 12 Id 24 i o50 i» ♦» ^:^ /v/7t A.3 »» >» 4.8 n 11 A.I »» »i 3.6 1, „ 3.9 /v/^e sand 3.0 i) m 4.4 /7/7ff sandy Zoom and fine send 3.3 »» »» 31 t» i» 3.1 Fine sand and crave/ 3.3 » »> 2.4 Fine sandy loom and fine sandy 3.3 Fine sand 2.S /v^ff sand ond onai/et 1.8 F/ne sondy Zoom sand and grave/ 2.8 % 2.6 M >» 2.0 Grave/ \ Fine sand T" | and gmve/ Fig. 6. — Diagram showing root distribution of alfalfa under varying irri- gation treatments at University Farm, Davis. Note that the root distribution has apparently not been affected by variation in irrigation treatments. tfepth in inches ! ^ ^ 5 Co $ ^ ■s. JO Cu * ! M 11 (b 5 °2 QD QT5 p 4 5 1 i 1 1 CD c+- o o* o pj N 0, >* to it <* k b Oj N :-»« &» £5 Cb Co N I ? Co is 1| 1 5 p s 31 ~ ! la ^ i ! 5 - - CD P N Co Ca> 0\ b fc & ^ 5 ^ 5 s ^ ^ fe 111 CD p 3 B M. CD -• ,. -» I? „ i» „ ^ p rt- trt- 05 5*53 CD CD P K B - go 3 3 ^ 1 1 Hi' o p" 3 I O Co N n Co On •* ! Ill So CD P CD * - • it : : 14 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Conclusions on Irrigation of Alfalfa at Davis and Delhi. 1. At Davis, the average maximum yield and the average maxi- mum profit were produced with total seasonal applications of 36 acre- inches to the acre, but the difference between the yields produced by 30 inches and those produced by 36 inches is so slight that it is not significant; 30 acre-inches per acre, therefore, can be considered an economic seasonal application under the conditions present, 2. Total depths of less than 24 inches annually, exclusive of rain- fall, are insufficient for satisfactory yields. Applications of depths of 48 inches or more annually produce smaller yields than were obtained by applying 36 inches. 3. Variation in the number of irrigations (three to twelve), when a total seasonal depth of 30 inches was applied, caused only small differences in yield. The lighter applications given at more frequent intervals tended to produce the higher yields, but the increases in yields did not warrant the extra labor cost and the inconvenience of applying frequent light irrigations. In loam soils, under Sacramento Valley conditions, a total seasonal application of 30 inches applied in four irrigations represents good irrigation practice for alfalfa. Obser- vations in other localities have shown that the very open or very impervious soils should be irrigated more than once between cuttings. 4. At Delhi, the maximum yields were produced by 42 acre-inches of water to the acre, or by six inches more than was required at Davis — an amount about equal to the difference in rainfall between the two stations. 5. Even in the light soil at Delhi, variations in number of irri- gations, providing the same seasonal total was applied, did not materi- ally affect the yield. No doubt the impervious layer at a depth of about six feet prevented the loss of a. large part of the water applied in the heavy irrigations, this water being used by the crop in the interval between irrigations. 6. Under field conditions, both at Davis and at Delhi, during a period when the winter rainfall was sufficient to moisten the soil to a depth of at least six feet, and where the depth to the underground water table was more than 15 feet, variation in depth of application or in frequency of irrigation did not affect the root distribution of the alfalfa. 7. On the average, at Davis, 52 per cent of the roots by weight were found in the top foot and 71 per cent in the top two feet of soil. At Delhi, the top foot contained 56 per cent of the roots and the top two feet 78 per cent. Only the top six feet of soil was considered. Bul. 450] IRRIGATION INVESTIGATIONS WITH FIELD CROPS 15 INVESTIGATIONS OF MISCELLANEOUS FIELD CROPS AT DAVIS, 1910-1925 From 1912 to 1915, a crop rotation plan was outlined for blocks 1 to 6, shown in figure 1. This plan is shown in the following table. TABLE 8 Rotation Plan of Field Irrigation Experiments at Davis, 1912-1915 Area, acres Crop Block 1912 1913 1914 1915 j 1.79 1.89 1.84 2.33 2.64 1.55 2 3 Grain(barley and wheat) 4 Grain (wheat and oats).. 5 Grain (barley) 6 The cropping followed from 1916 to 1925 is shown in figure 2. Irrigation of Wheat, Oats, and Barley. — These investigations covered a period of eleven years, beginning in 1910 and terminating in 1921. From 1912 to 1915, the trials were carried on as a part of the crop-rotation scheme covering a period of the four years outlined above. It was intended that the work with wheat and oats should extend over a longer period than was covered. It was found, however, that a TABLE 9 Period Covered by the Grain Investigation and the General Plan of Irrigation Treatment Crop Year Irrigation treatment Remarks Barley 1910-1916 One, two, or three spring irrigations applied as indicated by crop needs. 1910-1911 on old grain land, 1912-1916 a part of rotation scheme of field crops following alfalfa. Barley 1913-1921 Summer and fall irrigation before seeding. Each year plot 1 received no irrigation, plot 2 was thoroughly irrigated immedi- ately after harvest and fallowed, plot 3 was irrigated each year prior to fall seeding. 1913-1921 cropped continuously to barley on land on which only grain had previously been raised. Wheat 1912-1914 One or two spring irrigations applied accord- ing to crop needs. As a part of the rotation of field crops following alfalfa. Oats 1912-1913 One or two spring irrigations applied accord- ing to crop needs. As a part of the rotation of field crops following alfalfa. TABLE 10 Kesults of Spring Irrigation of Barley, 1910-1916 (at Davis) Season Seasonal rainfall, inches Plot Area, acres Number of irrigations Depth of water applied, inches Yield grain, pounds per acre Ratio grain to straw Cost of irrigation, per acre Crop of previous year 11.90 6A 6B 6C 1.25 0.50 0.50 1 2 1,160* 1,480* 1,840* 1:1.70 1:1.32 1:1.86 Barley Barley Barley 1910 3.6 6.2 $1.08 1.86 23.18 6A 6B 1 A IB 1C 0.72 0.67 0.50 0.50 0.50 1 (late) 1 (early) 1 (early) 2 850* 1,515* 1,108 2,146 1,810* 1:0.82 1:0.79 1:0.84 1:0.75 1:0.76 Barley Barley Barley Cow peas Barley 1911 5.6 4.3 6.0 7.0 $1.68 1.29 1.80 2.10 9.46 6A 3 A 3B 3C 1.48 0.49 0.48 0.49 1 2 346 1,040* 1,285* 1,950* 1:0.95 1:0.89 1:1 15 1:0.94 1912 Alfalfa 7.4 16.9 $2.22 5 07 Alfalfa Alfalfa 8.74 6A 7A 7B 7C 1.10 0.25 0.25 0.25 1 2 448 320* 2,144* 2,556* 1:0.95 1:2.75 1:1.50 1:2.60 Barley 1913 9.2 13 4 $2.76 4.02 Corn Corn 28.70 6 A 5 A 5B 5C 5D 1.20 0.57 0.19 0.19 0.19 1 1 1 1,790 2,070* 1,955 2,535* 2,695 1:1.08 1:1.20 1:2.38 1:1.50 1:1.30 Barley 1914 4 8.0 12 $1.20 2.40 3.60 Potatoes Potatoes Potatoes 20.05 6A 1 A IB 1C 1 D IE 51 0.26 0.25 0.25 0.25 0.25 1 1 1 1 1,325 1,970* 2,085 2,085 2,165* 2,210 1:1.81 1:1.43 1:1.28 1:1.39 1:1.29 1:1.20 Barley 1915 3.0 4.5 6.0 7.5 $0.90 1.35 1.80 2.25 Sugar beets Sugar beets Sugar beets Sugar beets 1916 20.88 2A 2A 3.90 4.00 1 1,188* 1,460* 1:2.90 1:3.00 Barley Barley 3.2 $0.96 Yields used in preparing table 11. TABLE 11 Comparison of Yields After Seasons of Light and Heavy Eainfall (at Davis) Seasons Average seasonal rainfall, inches Number of irriga- tions Average depth of water applied, inches Average yield* of grain, lbs. per acre Ratio grain to straw Cost of irrigation per acre 1910, 1912, 10.07 1 2 6.7 12.2 840 1,636 2,115 1:1.78 1:1.32 1:1.80 1913 $2.02 3.65 1911, 1914, 23.20 1 2 5.2 7.0 1,520 1,780 1,810 1:1.58 1:1.72 1:0.76 1915, 1916 $1.56 2.10 * In preparing table 11, yields marked with an asterisk (*) in table 10 were used. Results obtained from plot 6 A in 1912-1915 were eliminated, since a fair comparison could not be made between an unirri- gated area continuously planted to barley and an unirrigated area under crop rotation. TABLE 12 Results of Irrigation of Barley Land Before Seeding, 1913-1921 (at Davis) Season Seasonal rainfall, inches Irrigation treatment Depth water applied, inches Yield grain, pounds per acre Ratio grain to straw Cost of irriga- tion 1913 8.84 438 3,306 1:0.99 1:1.25 One fall irrigation before seeding 12.0 $3.60* 28.70 1,790 2,000 1:1.08 1:1.11 1914 10.0 $3.00 20.05 1,325 1,330 1,460 1:1.81 1:1.75 1:2.09 1915 9.0 9.0 $2 70 One summer irrigation before seeding .... 2.70 20.88 1,280 1,555 1,555 1:1.13 1:1.50 1:1.16 1916 10.3 10.3 $3 09 One summer irrigation before seeding ... 3.09 14.11 2,505 2,311 2,258 1:0.81 1:0.99 1:1.33 1917 11.3 11.3 $3 39 One summer irrigation before seeding ... 3.39 9.66 714 1,595 1,515 1:1.67 1:1.74 1:2.56 1918 9.2 9.2 $2 80 One summer irrigation before seeding ... 2.80 19.40 2,285 1,330 1,913 1919 One fall irrigation before seeding One summer irrigation before seeding ... 10.7 10.7 $3 21 3 21 8.94 202 1,332 1,702 1:2.32 1:2.00 1:1.75 1920 One fall irrigation before seeding One summer irrigation before seeding .... 10.2 10.2 $3.06 3.06 16.92 Nonef 2,483 2,935 1921 11.2 11.2 $3 06 One summer irrigation before seeding .... 3 06 * Cost of irrigation (water and labor) figured at 30 cents per acre-inch. t Climatic conditions did not permit seeding until Feb. 11, and crop did not reach sufficient height to be harvested. TABLE 13 Comparison of Yields of Barley After Seasons of Light and Heavy Rainfall (at Davis) Seasons Average seasonal rainfall, inches Irrigation treatment Depth water applied, inches Yield grain, pounds per acre Ratio grain to straw 1913, 1917, 11.69 772 2,205 2,102 1-1 45 1918, 1920, 10.8 10.8 1-1 50 1921 1*1 88 1914, 1915, 22.26 1,670 1,554 1,643 1 - 1 23 1916, 1919 10.5 10.5 1*1 45 1:1.62 All years 1913-1-921 16.35 1,171 1,916 1,905 1:1.36 1:1.48 1:1.78 10.6 10.6 18 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION very appreciable portion was shattered each year during heavy north winds, making it impossible to obtain a true measure of the yields, when the crops were allowed to ripen. The plan of the experiments is outlined in table 9. Tables 10 to 15 give the data obtained. A comparison of the yields with the corresponding depths of water applied is made in figure 8. TABLE 14 Results of Spring Irrigation of Wheat, 1912-1914 (at Davis) Season Seasonal rainfall, inches Plot Number of irriga- tions Depth of water applied, inches Yield grain, pounds per acre Ratio grain to straw Cost of irrigation* 564 1:2.10 1912 9.46 1 1 10.0 1,210 1:2.25 $3.00 2 2 17.6 1,930 1:2.26 5.28 1 1 2.0 127 566 1:3.89 1:5.50 $0.60 2 1 4.0 1,315 1:2.33 1.20 3 2 6.0 1,605 1:3.15 1.80 4 2 8.0 1,632 1:3.00 2.40 1913 8.74 5 2 10.0 1,792 1:3.12 3.00 6 2 12.0 1,610 1:2.90 3.60 7 2 15 1,240 1:3.64 4.50 iot lit 1,354 1:1.72 1 6.8 1,730 1:1.92 2.04 12t 2 13.0 1,872 1:2.22 3.90 1 1 4.0 1,225 946 1:3.70 1:3.71 $1.20 1914 28.70 2 1 8.0 913 1:4.55 2.40 3 2 12.0 853 1:4.61 3.60 4 2 16.0 818 1:4.20 4.80 5 2 20.0 776 1:4.14 6.00 * k Cost of irrigation (water and labor) figured at 30 cents per acre-inch. t In cow peas, season 1912. TABLE 15 Results of Spring Irrigation of Oats, 1912-1913 (at Davis) Season Seasonal rainfall, inches Plot Number of irriga- tions Depth of water applied, inches Yield grain, pounds per acre Ratio grain to straw Cost of irrigation* 1912 9.46 1 2 1 2 13.2 21.8 437 1,470 2,050 1:2.25 1:2.32 1:1.84 $3.96 6.54 1913 8.74 1 2 1 2 8.1 15.8 1,016 1,508 1:3.86 1:4.33 $2.43 4.74 * Cost of irrigation (water and labor) figured at 30 cents per acre-inch. BUL. 450] IRRIGATION INVESTIGATIONS WITH FIELD CROPS 19 eaoo 2000 1800 Uiree Y^ars- Average Seasonal Painfoli 10.07 in. /600 q. ^/400 ^k^/ooo ^ %soo ilooo Four Yeorsj Average 5eosona/ Rainfall £3.3 in. % i 400 eoo o e 6 S 10 12 a o Number of Irrigations Fig. 8. — Diagram showing results of spring irrigation of barley at University Farm, Davis, 1910-1916. Note the heavy increase in yield due to irrigation in dry years and the comparatively low increases in years of heavy rainfall. Conclusions on Irrigation of Grain. 1. Under Sacramento Valley conditions, with a seasonal rainfall of 17 inches or more, normally distributed, the increase in grain yields do not warrant irrigation. 2. In years of deficient rainfall, normal yields of grain may be produced with irrigation. The number of irrigations and depth of 20 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION water which should be applied in years of deficient rainfall depends upon the rainfall and its distribution, and general weather conditions during the growth of the crop. 3. Under conditions of extreme rainfall deficiency, such as 1910, 1912, and 1913, two irrigations of four to six acre-inches to the acre should be sufficient to produce normal yields. Under conditions of partial drought, especially where a deficiency of rainfall occurs in the late winter and early spring (March and April), satisfactory yields may be obtained through one irrigation. 4. In years of heavy rainfall, irrigation may produce a decrease in yield. However, if this rainfall should be unequally distributed, with a deficiency during March and April, irrigation water may be applied with advantage. 5. Irrigation of grain land before seeding (either in the summer or in the fall just prior to seeding) produces no increase in yields in years of normal rainfall. In years of deficient rainfall, normal yields will be produced by this method of irrigation. In years of drought the average yield produced by this method was one-third greater than the average yields produced in years of normal rainfall. 6. According to the results obtained in the eight years covered by these experiments, there have been six years out of the past eighteen years (1909-1926), at the University Farm, Davis, when irrigation would probably have produced no material increase in yields; six years in which the distribution and amount of rainfall was such that one spring irrigation could have been applied with advantage; and six years in which two irrigations would have been required for full production. Irrigation of Corn and Grain Sorghum, 1910-1922 (at Davis). — Investigations with these crops were started in 1910 and continued through 1915. In 1922, the work was started again on another tract of the University Farm, but a readjustment of experimental areas forced a temporary discontinuation at the end of that season. In the production of corn and grain sorghum, standard practices in the preparation of seed bed, seeding, cultivation, and harvesting were followed, the only variable factors being the frequency of irri- gation and depths of water applied. In irrigation, the furrow method was used. A thorough cultivation followed each application of water. The water applied was measured by temporary weirs installed in the field laterals. &s Depth of /rr/'gat/on Y/e/o* of Ehs/fcrge /'n inches in tons per acre 22 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The results of yields under varying irrigation treatment in years of light, average, and heavy rainfall are shown in figure 9. TABLE 16 Eesults of Irrigation of Indian Corn, 1910-1915 and 1922 (at Davis) Season Seasonal rainfall, inches Plot Area of plot, acres Number of irriga- tions Depth water applied, inches Yield of ensilage tons per acre Cost irriga- tion* Crop of previous years 0.67 6.91 1910 11.90 1 0.32 1 3.3 8.84 $1.82 1908, barley 2 0.32 2 5.3 10.00 3.12 1909, sugar beets 3 0.67 3 8.0 10.50 4.70 0.54 3.67 1908, barley 1911 23.18 1 0.54 1 2.3 4.86 $142 1909, sugar beets 2 0.54 2 4.7 5.22 2.88 1910, Indian corn 3 0.54 3 7.1 6.88 4.34 0.31 3.66 1912 9.46 1 0.35 1 4.0 4.57 $2.10 1909-1911, alfalfa 2 0.35 2 8.6 5.81 4.42 3 0.35 3 14.6 6.60 7.32 0.26 1.54 1 0.26 1 3.0 3.80 $1.70 1913 8.74 2 0.26 2 6.0 3.36 3.40 1909-1911, alfalfa 3 0.26 3 9.0 4.99 5.10 1912, potatoes 4 0.26 4 12.0 6.74 6.80 5 0.26 5 15.0 7.05 8.50 0.27 3.93 1 0.27 1 4.0 7.38 $2.10 2 0.27 2 8.0 11.48 4.20 1909-1911, alfalfa 1914 28.70 3 0.27 3 12.0 12.02 6.30 1912, oats 4 0.27 4 16.0 11.65 8.40 1913, sugar beets 5 0.27 4 19.2 11.70 9.68 6 027 4 23.2 11.83 11.28 0.63 4.02 1909-1911, alfalfa 1915 20.05 1 0.56 1 4.0 9.87 $2.10 1912, sugar beets 2 0.59 2 8.0 12.22 4.20 1913, wheat 3 54 3 12.0 14.15 6.30 1914, potatoes 50, 51, 52, 0.38 4.00 47, 48, 49, 0.38 1 3.0 4.96 $1.90 1913-1917, alfalfa 1922 16.62 44, 45, 46, 0.38 2 5.8 6.92 3.32 1918, barley 19, 20, 43, 0.38 3 11.3 8.35 4.84 1919-1921, corn 16, 17, 18. 0.37 4 15.7 8.16 8.28 * Cost of irrigation (water and labor) figured at 40 cents per acre-inch; irrigation furrowing at 50 cents per acre per irrigation. BUL. 450] IRRIGATION INVESTIGATIONS WITH FIELD CROPS 23 TABLE 17 Summary and Comparisons of Yields, Indian Corn (Ensilage) Following Seasons of Light and Heavy Eainfall (at Davis) Years Average sea- sonal rainfall, inches Number of irrigations Depth water applied, inches ..... v Yields, tons per acre Cost of irrigation per acre* 1910, 1912, 1913 (dry years) 9.97 2 3 3.4 6.6 10.5 4.04 5.73 6.40 7.36 SI. 86 3.64 5.70 1911, 1914, 1915, 1922 (wet years) 22.14 1 2 3 4 3.6 6.8 10.6 15.8 3.91 6.77 8.96 10.35 9.90f $1.94 3.72 5.74 8.32 1910-1915, 1922 16.95 2 3 4 3.5 6.7 10.6 14.6 3.98 6.33 7.86 9.07 8.851 $1.90 3.68 5.74 7.84 * Cost of irrigation (water and labor) figured at 40 cents per acre-inch; irrigation furrowing at 50 cents per acre per irrigation. t Average of 2 years only (1914, 1922). % Average of 3 years only (1913, 1914, 1922). TABLE 18 Eesults of Irrigation of Dwarf Milo Maize, 1910, 1911, 1913, and 1922 (at Davis) Season Seasonal Rainfall, inches Plot Area of plot, acres Number of irriga- tions Depth of water applied, inches Yield of grain, pounds per acre Cost of irriga- tion* Crop of previous years 1910 11.90 1 2 0.30 0.30 0.30 1 2 3.8 5.5 1,340 2,680 2,710 $2.02 3.20 1908, barley 1909, sugar beets 1911 23.18 1 2 3 0.54 0.54 0.54 0.54 1 2 3 1.8 4.6 5.6 1,018 1,565 2,453 2,530 $1.22 2.84 3.74 1908, barley 1909, sugar beets 1910, dwarf milo 1913 8.74 1 2 3 4 5 6 0.26 0.26 0.26 0.26 0.26 0.26 0.26 2 3 4 5 6 3.0 6.0 9.0 12.0 15.0 18.0 230 614 998 1,074 1,343 1,842 $1.70 3.40 5.10 6.80 8.50 10.20 1909, 1911, alfalfa 1912, barley 1922 16.63 74, 75, 76, 77, 78, 79, 80,81,82, 83, 87, 84, 85, 86. 0.25 0.36 0.37 0.37 0.37 1 2 3 4 3.4 7.1 11.1 13.6 3,835 4,295 5,187 5,152 5,747 $1.86 3.84 5.94 7.44 1913-1917, alfalfa 1918, barley 1919-1921, corn * Cost of irrigation (water and labor) figured at 40 cents per acre-inch ; irrigation furrowing at 50 cents per acre per irrigation. 24 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE 19 SUMMARY OF IRRIGATION OF DWARF MlLO MAIZE, 1910-1911, 1913, AND 1922 Years Average sea- sonal rainfall, inches Number of irrigations Depth water applied, inches Yield in grain, pounds per acre Cost of irrigation* 1910, 1911. 1913. 1922 15.11 1 2 3 3.0 5.8 8.6 1,548 2,192 2,741 2,893 $1.70 3.32 4.94 * Cost of irrigation (water and labor) figured at 40 cents per acre-inch ; irrigation furrowing at 50 cents per acre per irrigation. Conclusions on Irrigation of Corn and Grain Sorghum (at Davis). 1. On medium soil types and in years of normal rainfall in the Sacramento Valley, the net irrigation requirement for full crop pro- duction should not exceed 12 acre-inches per acre, applied in not more than three irrigations. 2. In years of deficient rainfall the net seasonal irrigation require- ment for these crops should not exceed 18 acre-inches, applied in not more than four irrigations. 3. Irrigation of land before seeding is advisable when rainfall conditions have been such that a proper seed bed cannot be prepared, or where there is not sufficient moisture in the surface soil to insure a proper germination of the seed. 4. Under the furrow method of irrigation a normal depth of irri- gation is 4 acre-inches per acre for each irrigation. 12m-3,'28