UNIVERSITY OF CALIFORN I A PPBLICATION8 COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE ECONOMICAL IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY BY S. H. BECKETT and R. D. ROBERTSON (Based on work done under co-operative agreement between the Office of Public Roads and Rural Engineering and the State Engineering Department of California and between the Office of Public Roads and Rural Engineering and the University of California Agricultural Experiment Station.) BULLETIN No. 280 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. fFRANK 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. t In co-operation with office of Public Roads and Rural Engineering, U. S. Department of Agriculture. THE ECONOMICAL IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 1 BY S. H. BECKETT AND E. D. ROBERTSON SUMMARY PRACTICAL SUGGESTIONS FOR SACRAMENTO VALLEY ALFALFA GROWERS For Medium Loams 1. Depth of irrigation water required per annum to produce the best yield of alfalfa from medium loam soils in Sacramento Valley 30 to 36 inches, depending on rainfall ' 2. Desirable depth of irrigation water to apply to alfalfa on medium loam soils at each irrigation 6 to 9 inches, depending on depth of soil 3. Usual number of irrigations per season for alfalfa on medium loam soils in Sacramento Valley where water supply is sufficient 3 to 5 4. Desirable size of border or strip checks for alfalfa on medium loam soils 30 to 50 feet wide by 300 to 600 feet long, depending on grade and soil 5. Desirable grades for border checks on medium loam soils 3 to 6 inches per 100 feet 6. Size of irrigating ' ' head ' ' most common for alfalfa on medium loam soils in border checks of this size in Sacramento Valley 2 to 10 cubic feet per second per check For Very Gravelly or Sandy Soils 7. Depth of irrigation water required per annum with careful practice for alfalfa on very gravelly and sandy soils in Sacramento Valley 48 to 60 inches 8. Desirable depths of irrigation water to apply to alfalfa on very gravelly and sandy soils at each irrigation 3 to 4 inches 9. Desirable number of irrigations for alfalfa on very gravelly soils in Sacra- mento Valley 2 to 3 per cutting 10. Desirable size of rectangular checks for alfalfa on very gravelly or sandy soils in Sacramento Valley 100 feet by 100 feet 11. Desirable size of irrigating "head'' for alfalfa on very gravelly soils in checks of this size 5 to 6 cubic feet per second per check For Heavy Soils 12. Depths of irrigation water required per annum for alfalfa on ll heavy" soils in Sacramento Valley (clays and clay loams) 30 to 36 inches 13. Desirable depth of irrigation water to apply to alfalfa on heavy soils at each irrigation 2 to 4 inches 14. Desirable number of irrigations for alfalfa on heavy soils in Sacramento Valley 2 to 3 per cutting 15. Desirable size of border or strip checks for alfalfa on heavy soils 30 to 50 feet wide by 300 to 600 feet long, depending on grade and soil 16. Desirable grades for border checks on heavy soils 1 to 3 inches per 100 feet 17. Desirable size of irrigating "head" for alfalfa on heavy soils in border checks of this size 1 to 4 cubic feet per second 1 This bulletin presents a brief resume and summary of a more complete report of the investigations discussed, prepared under the joint authorship of 274 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION INTRODUCTION From two and one-half to three acre-feet of irrigation water per acre per year is sufficient for the growth of maximum economic yields of alfalfa on the medium loam soils of Sacramento Valley. This is the conclusion drawn from experiments covering a six-year period at the University Farm at Davis, and of observations during one to two years on fifty-four Sacramento Valley alfalfa farms. In addition to the particular studies from which the above con- clusion is drawn, these experiments and observations have been con- cerned with the duty of water for alfalfa on botli the lighter and the heavier soils of the valley, the quantities of water it is desirable to apply to Sacramento Valley alfalfa fields at single irrigations, desirable irrigation ' ' heads ' 7 for Sacramento Valley alfalfa fields, the percentage of moisture in the soil necessary to prevent wilting, and the amount of moisture above the wilting percentage that produces the most satisfactory growth. EXPERIMENTS AT THE UNIVERSITY FARM AT DAVIS The duty-of-water experiments conducted at Davis covered the period 1910 to 1915, inclusive. During 1910 and 1911, 8.19 acres in square and contour checks, each 0.20 to 1 acre and averaging 0.28 acre in area, were utilized. From 1912 to 1915 the work was confined to 3.48 acres divided into 15 square checks averaging 0.23 acre each. The soil of these plats is classed by the Bureau of Soils and the University of California Agricultural Experiment Station as Yolo loam. 2 In addition to check plats which were not irrigated, the various annual depths of water applied were 12, 24, 36, and 48 inches, for the full six years of the experiment, with additional plats receiving annual Frank Adams, Ralph D. Robertson, S. H. Beckett, Wells A. Hutchins, and O. W. Israelsen, printed in the fifth biennial report of the California State Department of Engineering, and reprinted as Bulletin No. 3 of that department. The investi- gations were made as a part of the co-operative irrigation investigations in Cali- fornia conducted under agreement between the Office of Public Roads and Rural Engineering (prior to July 1, 1915, the Office of Experiment Stations) of the United States Department of Agriculture, the State Department of Engineering of California, and the California Agricultural Experiment Station. The work at the University Farm at Davis has been under the local supervision of Professor S. H. Beckett, assisted by O. W. Israelsen and Roy Wray. The work on Sacra- mento Valley alfalfa farms and on the temporary experimental plat at Willows was done under the immediate supervision of Ralph D. Robertson, assisted chiefly by Wells A. Hutchins. Soil moisture studies were largely made by O. W. Israelsen. 2 U. S. Dept. of Agr., Bureau of Soils, Reconnoissance Soil Survey of the Sacramento Valley, California. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 275 depths of 18 inches and 60 inches during the last four years of the experiment. The total depths of 30, 36, 48, and 60 inches were given in indi- vidual applications of 7.5 inches, 9 inches, 12 inches, and 15 inches, respectively. In 1910, 1912, and 1913, following winters of low rain- fall, the first irrigations were given immediately after the first cuttings, but in 1911, 1914, and 1915, following relatively wet winters, irrigation began after the second cutting. All of the plats were large enough to represent normal field practice, so the work should be classed as field experiments rather than laboratory experiments. Irrigation water was supplied from a pumping plant on the tract delivering approximately 0.9 cubic foot per second. Throughout the experiments the practice followed was to irrigate just as soon as possible after removing the crop from the field. Be- cause of the small irrigating head available, slip-joint pipe was used on the larger checks to aid in even distribution. In the time of cutting, raking, shocking, and hauling the hay standard field practices always were observed. That is to say, the alfalfa usually was cut when one-tenth to one-third in bloom and the hay generally was raked the same day, shocked the following day, and hauled as soon as it was dry enough to be stacked without heating, never being left until the leaves were dry enough to fall off when handled. The curing and removal of the hay from the field required from five to seven days. The following table summarizes the results of these experiments at Davis over the full six-year period, including the average cost of production and the average profit per acre : TABLE NO. 1 Summary of Alfalfa Duty-of-Water Investigations at Davis, 1910-1915 CO O o CB cS to " SI ••* 'u u u •si s* Yield, tons per acre A £H 3 c3 S > ? * UJG&- ^ ^ .^ 8-2 o u a> u ^ u 0> Jj 1910 1911 1912 1913 1914 1915 Average 3 ft None 3.85 5.94 5.52 2.75 2.89 2.35 3.88 $27.16 $8.73 $18.43 2 6 12 4.78 7.52 6.51 4.31 5.83 4.84 5.63 39.41 15.37 24.04 3 6 18 7.02 5.69 8.02 6.46 6.80 47.60 19.35 28.25 4 6 24 6!6o 8^38 8.32 6.89 9.96 7.96 7.92 55.44 23.22 32.22 4 71 '2 30 7.53 9.54 9.43 7.97 11.06 8.32 8.98 62.86 26.45 36.41 4 9 36 7.58 9.33 9.38 8.22 12.48 8.63 9.27 64.89 27.96 36.93 4 12 48 8.45 9.52 8.63 8.83 10.62 8.05 9.02 63.14 29.10 34.04 4 15 60 10.17 7.25 10.70 5.55 8.42 58.94 29.44 29.50 Market val ue of hay, 1910, 1911, and 1912, $11 per ton; 1913, $9; 1914, $4; 1915, $8. 2 Labo Water figi r of production, inclui ured at $1.70 per acre ling cutting, raking, shock -foot. Labor for irrigation ing, and hauling, figured at $2.25 per ton. figured at 50 cents per acre per irrigation. 276 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Examination of this summary indicates that while both the average maximum yields and the average maximum profits were greatest in the case of annual applications of 36 acre-inches of irrigation water per acre, neither the average increase in yield nor the average increase in profits, with applications at the rate of 36 acre-inches per acre per year, over the average yields and profits with applications at the rate DEPTH OF IRRIGATION IN INCHES 12 16 Z4 30 36" 43 60 ii I II ■ II II I m ii n ii ii i i ii n ii i ii ii i ■ ■ ii ii i ii ii ii 1 1 ii 1 1 Fig. 1. — Diagram showing results of alfalfa duty of water experiments at University Farm, Davis, 1910 to 1915. Note the maximum yield with an annual application of 36 inches of water. The most economical yields were obtained with annual applications of 30 to 36 inches. of 30 acre-inches per acre per year, was large enough to be material, with water costing at the rate figured in the Davis experiments. It is plain, however, that to the extent that water costs less than $1.70 per acre-foot the increase in net profits with annual depth of 36 inches over the figures for annual depths of 30 inches would be correspond- ingly greater, and very much greater if water were paid for at the IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 277 flat annual rate of $1.50 or $2 per acre, as was the case in a number of the Sacramento Valley areas included in the general investigation. The significant fact about the results at Davis is that the increase in yield tends to become negligible above annual depths of 30 to 36 inches, indicating that under conditions at Davis, or similar thereto, a maximum allowance of 36 acre-inches per acre per year is ample. This is further brought out graphically in the accompanying chart (fig.D. The most marked change from year to year in the relation of the averages to each other took place in the 60-inch applications. The 1912 yield from the most heavily irrigated plat was more than 10 tons per acre, but the average dropped to 8.42 tons per acre by 1915, and had the investigations been conducted longer this average doubtless would have decreased each year. The 1915 yield was only 5.55 tons per acre, owing to the quantity of rank water grass which had sup- planted the alfalfa. A wide variation in the seasonal rainfall and in the length of the growing season was observed at Davis. Both of these factors seemed to have a decided effect on the yields of hay, as shown by the following table : TABLE NO. 2 Eelation of Climate to Yields of Hay at Davis Season Rainfall Length of growing A Dates season 1 Number of days Average temper- ature, o F Number of cuttings Average yield of hay per acre from all checks 1909-1910 11.90 Mar. 22-Oct. 10 202 57.7 6 6.36 1910-1911 23.18 Feb. 27-Oct. 7 222 58.3 6 8.37 1911-1912 9.46 Mar. 3-Oct. 10 221 57.9 6 8.12 1912-1913 8.74 Mar. 4-Sept. 17 197 58.0 5 6.49 1913-1914 28.70 Feb. 6-Oct. 26 262 60.0 6 8.94 1914-1915 20.05 Jan. 23-Oct. 13 263 59.5 6 6.52 Average 17.00 Feb. 23-Oct. 9 228 58.6 7.48 1 Period between date of last killing frost in the spring and the date of cutting last crop the following fall. Immediately following the harvesting of the last crop at Davis, on October 13, 1915, five areas, each containing 100 square feet, were laid off on each plat included in the experiment and the number of plants in each area counted. The probable number of plants per acre was figured from the average of these counts. By field count a good stand of mature alfalfa was found to contain an average of one and one-half plants per square foot. With this as a basis of comparison, the following table was compiled : 278 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION TABLE NO. 3 /ENT OF Alfalfa Stand Remaining at I Six- Year Experimental Period Number of plats 17,30 Depth of water applied, in. Number of plants per acre 8,625 Per cent of good stand re- maining 13.2 18,29 12 22,216 34.0 19,28 18 30,928 47.3 20,27 24 33,977 52.0 21,26 30 41,382 63.3 22,25 36 39,422 60.3 23,24 48 38,333 58.7 31 60 17,598 26.9 This shows the effects of the two extremes in the application of water, especially when it is remembered that the observations on the 60-inch application extended over a period of only four years, and in this time the stand, as a result of over-irrigation, was reduced to an estimated average of only 27 per cent of the original. INVESTIGATIONS ON SACRAMENTO VALLEY ALFALFA FARMS In selecting the areas away from Davis to be included in the wider investigation care was taken to include enough fields so that there would be represented the major soil types of the valley, as determined by the soil surveys of the Bureau of Soils and of the University of California Experiment Station, whose soil classifications have been followed in this report; also to give the investigations as wide a geographical distribution as possible, so that the differences in rainfall could be taken into consideration. Accordingly, during the irrigation seasons of 1913 and 1914, between 40 and 50 representative farms were under observation in the neighborhood of Gridley, Los Molinos, Orland, Willows, Woodland, and Dixon, this work being supplemented in 1915 by detailed studies on a single ten-acre tract five miles northeast of Willows, and by general observations and measurements on four other farms. In every case where the amount of water used was measured the crop yields were ascertained by the most satisfactory means available. In some cases crops either were sold in bulk according to scale weights or baled, making exact weights available. In a few cases stacks were measured or a sufficient number of shocks to be representative of the whole were hauled to nearby scales and the average weight per shock obtained. In a large number of cases the average weight of shocks was ascertained by weighing on the ground. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 279 Table No. 4 below summarizes the results of the measurements on Sacramento Valley farms during 1913 and 1914. TABLE NO. 4 Summary of Results of Alfalfa Duty-of- Water Measurements on Fifty-four Farms in Sacramento Valley, 1913 and 1914 Name of area Average rainfall, in. Number of fields included covered by obser- vations Gridley 22.24 1 14 284.22 Los Molinos 26.11 2 12 130.40 Orland 19.23 7 214.52 Willows 16.55 3 27.71 Woodland 17.23 3 12 295.07 Dixon 17.23 3 6 207.17 Totals and avgs . 19.76 54 1159.09 1 Biggs record. 2 Red Bluff record. 3 Davis record. Years 1913 1913-14 1913-14 1914 1913-14 1913 Average total depths of water applied, ft. 3.31 5.15 4.66 1.83 2.33 2.94 3.37 Average total yields, tons per acre 6.19 6.01 6.26 4.82 6.45 6.76 6.08 If the amount of water used on Sacramento Valley farms, as indi- cated by the above table, were to be taken as the amount necessary to get maximum economic yield, it is evident that the results at Davis would not be applicable throughout the valley. The amounts of water applied, however, do not necessarily indicate the amounts needed. In many cases much more water was applied than was retained by the soil; and in the case of the compact soils about Willows it was not possible to get into the soil sufficient water to supply the needs of the crop. That the results at Davis are, in general, applicable throughout the valley, with the exception of the results on the highly pervious gravelly loams at Orland and the impervious Tehama clays and clay loams at Willows, was made plain from the approximately 11,000 soil- moisture determinations made on the Sacramento Valley alfalfa farms under observation during three years of the investigations. At Davis the amounts of water used were strictly under control, and, with the exception of the plat receiving a depth of 60 inches, single irrigations were, as a rule, not greater than the soil would retain, the soil-moisture determinations before and after irrigation showing that an average of 76.4 per cent of the water applied to plats which were given a depth of 6 inches in one irrigation was retained in the upper 6 feet of the soil, and that the plats given iy 2 , 9, and 12 inches per irrigation, making an average of 9% inches per application, retained an average of 60.6 per cent in the upper 6 feet of soil and 97.7 per cent in the upper 12 feet. The soil of the experimental irrigation tract at Davis is chiefly a fine sandy loam, relatively uniform, with no 280 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION impervious stratum, and with the ground water level below the normal feeding zone of the plant roots. The upper two feet are very uniform, but the third to eighth feet are of fine sandy loam, pocketed at irregu- lar intervals with coarse sand or clay loam. While at Gridley the sur- face soil of the fields under observation in 1913 does not vary greatly from the soil at Davis, most of it is underlaid with hardpan at depths of from four to six feet, and all of it contained free ground water at six feet or less from the surface. At Los Molinos, while the soil of some of the fields is comparable with that at Davis, being of silty or sandy loam and of relatively uniform depth for at least 12 feet from the sur- face, some fields have more clay and some are more gravelly than those at Davis. The normal rainfall at Red Bluff, which is the nearest point of observation to Los Molinos, is approximately nine inches greater than at Davis, and in the years 1913 and 1914 it was more than six inches above the average at Davis for the six years covered by the experiments there. An entirely different type of soil is found at Orland, all but one of the fields investigated having been made up largely of gravel. Here, also, water conditions differ considerably from those at Davis, a shortage of water in the late season in 1913 having made it necessary to eliminate one irrigation. A very wide departure in soil type is encountered at Willows, and, as indicated by the summaries of use on fields under investigation there, it was impossible to get enough water into the soil to satisfy the needs of the crop. While the soils at Woodland are generally com- parable with those at Davis, paying for irrigation water on a quantity basis rather than on an acreage basis, as at Gridley, Los Molinos, Or- land, and Willows, altered the Woodland practice materially. During the season of 1913 at Woodland, following a winter of low rainfall, the usual practice was to give at least three irrigations, and some farms received water six times, alfalfa bringing good prices that year, and water therefore being applied plentifully. In 1914, however, follow- ing a winter of more than normal rainfall, and when the price of alfalfa had dropped to nearly one-third the figure obtainable in 1913, no irrigators watered more than three times, and as a rule only two, with many not watering at all. Observations were made at Dixon during 1913 only. Water used there is obtained from pumping plants and use generally represents what the various irrigators consider to be necessary. While in this regard conditions at Dixon are similar to those which governed the experiments at Davis, the soil is considerably heavier than at Davis, and takes water much less freely. Gridley. — Analyzing the results obtained at Gridley, it was found that a maximum yield of 9.38 tons was obtained from a field which IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 281 received a total annual depth of irrigation water of 31.6 inches, but that the next nearest yield was only 7.28 tons per acre, obtained on a field which received 34 inches of water for the season. Eight out of the fourteen fields studied at Gridley received greater annual depths of irrigation water than 34 inches, but on three of these the yield fell below five tons, on four below six tons per acre, and on seven below seven tons. In other words, after eliminating the single field that had the excessive yield of 9.38 tons per acre, it was found that the point beyond which it did not pay to add to the depths applied cor- responds substantially with the points established in the Davis experi- ments, namely, between 30 and 36 inches. The seasonal rainfall at Gridley preceding the heaviest of these yields was 13.9 inches. Los Molinos. — Analyzing the results obtained at Los Molinos for the seasons 1913 and 1914, it is found that a maximum yield of 8.31 tons per acre was obtained with a total annual application of 47.4 inches, following an average rainfall for the two seasons of approxi- mately 24.4 inches. To what extent, if at all, excessive use here re- duced yields by soil leaching can only be conjectured. Seven of the 11 fields under observation received more irrigation water than the field of maximum yield, the maximum application being 84 acre-inches per acre. Of these seven fields, however, one yielded less than four and one-half tons per acre, four below six tons per acre, and six below seven tons per acre. At Los Molinos it is to be noted that both the maximum and the majority of applications were considerably in excess of the applications at Davis, but, as pointed out in the discussion of soil-moisture determinations in this area, the soils of the Los Molinos fields are highly permeable and the use of water was wasteful. Studies of the underground distribution of the irrigation water applied showed that beyond a doubt large quantities passed below a depth of six feet, single applications amounting, in numerous cases, to between 20 and 30 inches. Orland. — Averages for eight fields at Orland, where the soil is prevailingly gravelly, gave a maximum of 6.77 tons per acre, with a total annual application of 24.6 inches after an average seasonal rain- fall of 19.2 inches. The maximum yield at Orland was obtained on the field that received the least water, the yield from two of the seven remaining fields falling below five tons, and that from five falling below six tons. Of the whole eight fields water was applied in excess of 80 inches on two fields, in excess of 55 inches on three fields, and in excess of 45 inches on five fields. Willows. — With complete results available for only one year and from only three fields at Willows, but with these results verified by 282 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION special studies in 1915, it is evident that the results are in no way comparable with the results at Davis, this being due to the ' ' tightness ' ' of the soil of the Willows fields and the impossibility of getting irri- gation water into it in amounts sufficient to satisfy the plants. A maximum yield of only 5.39 tons was obtained at Willows with an application of 23.6 inches in addition to the seasonal rainfall of ap- proximately 28.7 inches for the preceding winter. Results at Willows indicate plainly that the soil-moisture needs of alfalfa, on the soils that hold moisture so tenaciously as do those at Willows, are in excess of the maximum applications found in 1914. Further, it is plain from the special studies in 1915 that to irrigate adequately the silty clay loams and the clay adobes of the Willows area water must be applied frequently and in small quantities, and at no time following the winter rainfall must the soil be allowed to dry out. The amount of water used on these Tehama clay soils is sure to increase as improvement in their physical condition, due to cropping and cultivation, makes them more pervious to water. Woodland. — Averages for the 12 fields at Woodland, for which full records are available, show a maximum yield of 8.81 tons per acre with a use of water of 29.7 inches in addition to an average seasonal rainfall of 18.3 inches. Three fields, which received depths of 23.5, 33.1, and 43.7 inches, gave respective yields of 7.60, 7.87, and 8.04 tons per acre. Taking seven fields for which the yields were most nearly equal, the range of variation being slightly over two tons and the average yield being 6.93 tons per acre, the average use was found to be a depth of 30.7 inches. Thus at Woodland it is found also that the usual maximum use, taking an average of one wet and one drv season, does not depart widely from that found most satisfactory at Davis ; also that the maximum average yield for one field during the two years of record was obtained with slightly less than 30 inches. Dixon. — Here the largest yield in the single year of observation was 9.97 tons per acre with a total depth of irrigation of 37.7 inches, in addition to a seasonal rainfall of 7.31 inches. The average use for six fields, from which complete records are available, was 35.3 inches, or again in close agreement with the Davis experiments. The. allowance necessary to be made for difference in local soil conditions and irrigation practice is, it is believed, fully established by the comparisons made above. In general, as already indicated, the statement is justified that the six-year record for Davis is applicable throughout the valley except to the very open soils such as those around Orland, and the silty clays and clay adobes found in these investigations in the neighborhood of Willows, but also existing else- IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 283 where in considerable areas. The average for Willows indicates, as already pointed out, that total irrigations of less than 24 inches per season are insufficient for satisfactory yields, while the results at Orland indicate that applications averaging in excess of 48 inches per year, while sometimes difficult to overcome on the very gravelly soils, do not give corresponding increases in tonnage. The average use at Woodland, which was below that at either Dixon or Gridley, was plainly a result of paying for irrigation water on a quantity rather than on a flat acreage basis. Finally, the average at Gridley illus- trates what may be expected on the open loam soils underlaid with hardpan or ground water. INVESTIGATIONS ON EXPEEIMENTAL TRACT AT WILLOWS Investigations on alfalfa farms near Willows in 1913 and 1914 disclosed a relatively small use . of irrigation water and correspond- ingly low yields of hay. Soil borings soon made it evident that irri- gation water was not penetrating sufficiently deeply into the soil to meet the needs of the alfalfa plants. In some cases irrigators who considered that they were applying an ample quantity of water were in fact wetting only the upper ten or twelve inches of soil, whereas normally at least the upper four to six feet should have had water. The heavy soils encountered in the investigations around Willows are classified in the soil survey as Tehama clay and clay loam. 3 These soils are all of compact structure and inclined to be refractory, very sticky when wet, and subject to hard baking when drying. As indicated in table No. 4 above, the average use of water on three farms at Willows in 1914 was 1.83 acre-feet per acre, and the average yield on six farms there in 1914 was only 4.82 tons per acre. In no single case was more than 1.97 acre-feet of water per acre applied per season, and none of the measured yields of alfalfa exceeded 5.39 tons per acre. For the purpose of ascertaining if more frequent irrigations would improve conditions on these heavy soils, a field of 8.75 acres about five miles northeast of Willows was utilized for experimental purposes during the season of 1915. This field was already in alfalfa and carried one of the best stands to be found in the immediate neighbor- hood. The field was divided into twenty-one border checks, 60 feet wide by 300 feet long, having an average grade of four inches per one hundred feet and an average area per check of 0.42 acre. 3 U. S. Dept. Agr., Bureau of Soils, Reconnoissance Soil Survey of Sacramento Valley, California. 284 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The soil in this field, which is classed as a Tehama clay loam, is grayish in color and of compact structure and refractory nature. When wet it is sticky, and upon drying becomes very hard, but does not check or crack. It is free from both hardpan and gravel and little difference is noticeable between the soil and subsoil. This type of soil was selected because the soil survey maps indicate the presence of about 45,000 acres of it in the Sacramento Valley, very largely east of Willows in the area surrounding this field. The amount of water used on each of the plats during the season was two acre-feet per acre, an average irrigation head of 2.82 cubic feet per second being generally divided between two checks, although various other sizes of heads were tried. One-third of the twelve checks under observation were irrigated with a depth of six inches, once for each cutting except the last, one-third received two three- inch irrigations between cuttings applied just before and just after the crop was removed, and one-third received three two-inch irriga- tions, at intervals of about 12 days. All of the water entering the field was measured by a 2 1 / ^-foot rectangular weir and automatic register. For the purpose of increasing, if possible, the perviousness of the soil to water, two checks were treated with ground limestone at the beginning of the season at the rate of four tons per acre. It was not expected that these checks would show much change the first year, and they did not. The largest annual yield of alfalfa, 5.07 tons per acre, was obtained from the checks receiving three two-inch irrigations per cutting, an increase of 18 per cent over the lowest yields, 4.42 tons per acre, being secured from the checks that received two three-inch irrigations per cutting, and lowest yield, 4.29 tons per acre, coming from the checks irrigated with one six-inch irrigation per cutting. While the above increases of yield indicate the desirability of more than one irrigation per cutting, the differences in the one season of investigations were not great. It was evident to those in the field, however, that the more frequent the application of water the better the moisture condition of the soil. Borings for soil-moisture determi- nations were difficult, except immediately after irrigations, and even then difficulty was encountered below the first foot of soil. Including the 12 plats, a total of 3408 moisture determinations were made before and after irrigations, and while the chief value of these is in the larger understanding they give of the character of these compact soils, especially with reference to the permeability to irrigation water they substantiate, to the extent reasonably to be expected, the better results due from the more frequent applications of irrigation water. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 285 In order to gain an idea of the root development of the alfalfa in this field, a hole about six feet square and three feet deep was ex- cavated. This also afforded a good view of the cross-section of the soil formation. The roots of the plants were carefully removed. It was found that the taproots of the alfalfa were not over one-half inch in diameter and did not extend below a depth of three feet. The main mass of the roots was concentrated in the upper two feet of soil. The fact that the greater part of the alfalfa plants in this particular field are shallow-rooted is attributed largely to the compact structure of the soil, making moisture penetration difficult. After removing the soil for root examination some rather sur- prising results were found in tests made by filling the hole from which they came with water and noting the time required for downward and lateral percolation. Twenty-four hours after the hole had been filled to a depth of three feet there remained in the hole two feet of water. Two weeks later there still remained one foot. Holes two inches in diameter and four feet deep bored 12 inches away from the large test hole showed no lateral percolation. In holes bored six inches from the test hole a slight amount of water had seeped through after 12 hours. Later another hole was excavated in a different part of the field and similar trials made, practically the same results being secured as in the first test. These tests serve to show the impermeability and peculiar physical conditions of the soil represented in this field. QUANTITIES OF WATER TO APPLY TO SACRAMENTO VALLEY ALFALFA FIELDS AT SINGLE IRRIGATIONS AS DETERMINED BY THE CAPACITY OF THE DIFFERENT SOILS TO RETAIN WATER At the outset of the investigations, one of the important practical questions presented was, How much irrigation water applied at one time, and added to that already present in the soil at the time of irrigation, would the various soils of Sacramento Valley retain ? While no particular effort was made in the investigations to ascertain how much irrigation water the various soils encountered would hold during the actual process of irrigation, 4 it was desired to ascertain how much would be retained after any surplus should pass through the soil; or, in other words, how much of the water applied would be retained against gravity. As the amount retained would depend largely upon the size of the soil particles, it was deemed best to have mechanical analyses made of the soil from a number of the fields under obser- vation. This was done by the Division of Soil Technology of the 4 This was however, indirectly ascertained through ' ' pore space ' ' determinations. 286 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION College of Agriculture of the University of California. Further, as the quantity of water soils will absorb and the rapidity with which it is absorbed depend to a considerable degree on the compactness of the soil, and, in order to determine what portion of the water applied in irrigation was retained by the soil, it was necessary to ascertain the volume weight of the soils "in place." This was done partly by standard laboratory methods, but chiefly by a special field method devised in the course of the investigations, and found to conform within satisfactory limits to other methods commonly used by investi- gators in more precise experiments. 5 The principal work in tracing the underground distribution of the irrigation water was done on fifteen fields — two at Gridley, four at Los Molinos, one at Orland, two at Willows, five at Woodland, and one at Dixon. With the possible exception of one of the fields at Woodland and the two fields at Willows, the soil sampling indicated that the capacity of the soil to retain water, assuming sufficient under- drainage to carry off the free water in the soil, was satisfied. A careful analysis of the results of the soil sampling and moisture de- terminations brings out the following facts that should be of practical interest to irrigators. 1. Pour times as much water was applied, on the average, to the silt loam soils with fine sandy loam subsoils as it was possible to apply, on the average, to the compact clay soils of the experimental tract at Willows, and more than three times as much as was applied to the clay soils of two of the fields at Willows. 2. Only about one-third of the water applied to the silt loam soils, as represented by five fields, was retained for the use of the alfalfa plants in the upper six feet of the soil, where the principal root development is located. 3. In the case of none of the 15 fields under observation did the amount of water retained per irrigation in the upper six feet of soil exceed 8.20 acre-inches per acre, 6 and in only two cases of the 15 did it exceed six acre-inches. s The method followed consisted in weighing all of the soil taken from holes carefully bored with a two-inch posthole type soil auger and then ascertaining the volume of this soil as it was "in place" by the use of a thin rubber tube inserted in the hole and filled with a known quantity of water. This method was ' ' checked ' ' against the laboratory method by use of the Bowman soil compactor, the iron cylinder, and the paraffin methods as applied to soils in place in a series of experiments conducted by Mr. O. W. Israelsen of this investi- gation and Professor Charles F. Shaw of the Division of Soil Technology of the College of Agriculture of the University of California. 6 Clay loam strata at depths varying from eight to ten feet caused partial waterlogging in overlying soil, hence the figure 8.20 is unusually high. All of the water in this soil was not retained against gravity. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 287 4. In only two cases out of ten in connection with the clay soils did the water that was absorbed by the upper six feet of soil reach four acre-inches per acre, in only three cases did it exceed three acre-inches per acre, and in four cases it was less than two acre-inches per acre. 5. The average quantities of water retained per acre-foot of soil per irrigation were 0.92 acre-inch for the silt loams with fine sandy loam subsoils, 0.71 acre-inch for the silt loams without fine sandy loam sub- soils, 0.58 acre-inch for the clay loams, and 0.37 acre-inch for the clays, not including the experimental tract at Willows, in every case less than one acre-inch per acre-foot of soil. 6. The maximum average quantities of water retained by the upper six feet of soil per acre-foot per irrigation were 1.02 acre-inches for the silt loams with fine sandy loam subsoils, 0.75 acre-inch 7 for the silt loams without fine sandy loam subsoils, 0.78 acre-inch for the clay loams, and 0.49 acre-inch for the clays. 7. Counting only the fields in which the full capacity of the soils to retain water against gravity was satisfied, i.e., all of the fields having loam soils except one field at "Woodland, the average water retained per irrigation in the upper six feet of soil was 4.31 acre-inches per acre, or only 32.6 per cent of the average individual applications, and only 0.72 acre-inch per acre-foot of soil. 8. Assuming that in every case the surface foot of soil received at each irrigation sufficient water to satisfy its full capacity to retain water against gravity, it is found from the detailed data at hand that the average for the 18 fields, including the experimental tract at Willows, was 1.23 acre-inches per acre, and that the averages for the different soil types were 1.08 acre-inches per acre for the silt loams, 1.35 acre- inches per acre for the clay loams, and 1.35 acre-inches per acre for the clays. Therefore, in the case of the typical silt loam soils of the Sacramento Valley, assuming one irrigation per cutting, single appli- cations of irrigation water exceeding a depth of one to one and one- half inches per foot in depth of the soil it is necessary to moisten, accomplish no useful purpose. The typical clay loams and clays of Sacramento Valley, in their normal condition of moisture, will absorb and hold against gravity as much as one and one-fourth to one and three-fourths inches in depth of irrigation water per foot of soil it is necessary to moisten; however, that amount of water will not be absorbed by these soils unless it is applied very slowly. 8 7 Not counting the field on which 8.20 acre-inches per acre were retained because of abnormal conditions previously referred to. 8 It is of interest here to note that with the surface foot of soil filled to its capacity to retain water against gravity the percentages of the pore space of the soil filled were as follows: for the silty loam soils, from 37 to 55 and averaging 288 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It seems evident from the figures given above that there is much ground for improvement in the matter of the quantity of water to apply to the alfalfa fields of Sacramento Valley at single irrigations. Had it been feasible to carry the soil-moisture determinations to a greater depth than six feet, the extent of the waste resulting from the large single applications would be still clearer. The data obtained are, however, sufficient to show clearly that the prevailing practice on Sacramento Valley alfalfa fields is to apply far more water at single irrigations than the more open soils have capacity to retain and than the more compact clay soils absorb under methods of application followed. A significant comparison can be made between the amounts of water retained by the soil in the case of the 15 typical Sacramento Valley alfalfa farms and the amounts retained in the case of six of the plats on the experimental tract at Davis, where the applications of water were under definite control. The average depth of water applied per irrigation to these six plats was 7.75 inches and the average quantity retained in the upper six feet of soil in the years 1913, 1914, and 1915 was 4.59 acre-inches per acre, or 66.8 per cent of the amount applied. On some of these plats, however, the borings for soil-moisture determinations were made to a depth of 12 feet, and it was found that within this depth practically all of the water applied was retained for the benefit of the plants. The average amount of water added by irrigation to the surface foot of soil in the Davis experiments was 1.45 acre-inches per acre. In other words, from the standpoint merely of the capacity of such deep loam soil as that at Davis to retain irri- gation water against gravity, and assuming that the lower depths will ' ' take up " as much water as the surface foot, the application once per cutting of one and one-half acre-inches of water per acre-foot, of soil it is desired to moisten, is not excessive. DESIRABLE IRRIGATION "HEADS" FOR SACRAMENTO VALLEY ALFALFA FIELDS In any investigation of the proper duty of water the size of the irrigation heads used and its relation to the type of soil irrigated, the method of irrigation followed, and the size and slope of the individual areas watered with a single head are always important. Fields may be evenly surfaced and levees perfectly made and proportioned, and yet the result will be excessive waste or inadequate absorption if the 45.5; for tlie clay loam soils, from 51 to 71 and averaging 62.2; for the clay soils, from 57 to 74 and averaging 65.5; and for all of the fields combined, 54.5. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 289 stream of water turned into each check is either too large or too small. The discussion as to what became of the water applied on a number of Sacramento Valley alfalfa fields, already presented, showed that where large quantities were applied to the open loam soils at single irrigations much of the water passed below the principal rooting zones of the alfalfa plants, and that the usual practice followed in irrigating the clay soils failed to accomplish sufficient penetration by the water. The stabilizing of the irrigation heads used in Sacramento Valley, with direct reference to the size of checks and the character of the soil, Fig. 2. — A thoroughly prepared alfalfa field ready for final harrowing and seed- ing. These checks do not exceed 500 feet in length or 40 feet in width. is obviously one of the very important irrigation problems of the valley. Quite extensive experiments and observations will be necessary for furnishing a satisfactory basis for fully understanding this problem, but the collection of some information bearing on the question was accomplished during the investigations in 1913 and 1914. This infor- mation was obtained from twenty -five fields — three at Gridley, two at Los Molinos, five at Orland, two at Willows, nine at Woodland, three at Davis, and one at Dixon. Five classes of soil were covered — gravelly loams, three fields ; sandy loams, four fields ; silt loams, nine fields ; clay loams, six fields ; and clays, ^.\e fields. Observations of the under- ground distribution of the water applied were made in connection with ten of the fields. 290 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION From an investigation of the data gathered in these investigations, it is evident that the most desirable head of water to use on any given soil can not be adequately determined by comparing use on different fields. The present general practice in Sacramento Valley, expressed in cubic feet per second per acre, is, however, satisfactorily indicated from the average figures obtained, namely, 23 for gravelly loams, 10.9 for sandy loams, 8.8 for silt loams, 7.3 for clay loams, and 3.2 for clays. The difficulty of irrigating porous soils with small heads and of irrigating clay soils with large heads is well recognized among irrigators, even if the most satisfactory relationships have not been worked out in detail. While a comparison of the rates of application on the different fields as given above fails to disclose the best size of head to use, a comparison of the relation between irrigation heads and depths of application on single fields makes it plain that in many cases either the head should be increased or, even better, the area of the checks reduced. Summarizing the rates and depths of application at different irri- gations of five individual fields, it was found, with minor exceptions, that in each instance, where the soil was sandy loam or silt loam, the depth of water applied increased as the rate of application decreased. In one case, due to the use of a relatively small head, a depth of 3.03 feet of irrigation water was used before the surface of the field was flooded. In four cases more than 2 feet in depth was applied per irrigation, and in fourteen cases out of twenty-seven the depth of application at each irrigation exceeded one foot. In order to carry this matter further, measurements of the amount of water required to cover a one-acre check, having a slope of 3% inches per one hundred feet, when applied at different rates were made at Davis. The data obtained were as follows : Rate of application, cu. ft. per sec. per acre 4.6 Depth of water required, ft. 2.75 10.1 1.86 13.5 1.16 15.3 0.84 17.8 0.69 Until the proper relation between irrigating heads and size of checks is satisfactorily worked out in Sacramento Valley soil, there is sure to be, there as well as elsewhere, much difference of opinion as to whether small checks and correspondingly small irrigation heads or large checks and correspondingly large irrigation heads should IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 291 prevail in the irrigation of alfalfa. Those who favor large checks and large heads base their preference chiefly on the greater rapidity with which irrigation can be accomplished with large heads, and also on the assumed lesser cost of preparing the land for irrigation. As a rule, where large heads are available they are used, and in some cases, as pointed out in connection with the heavy soils, especially the ' ' water- tight" soils found in some portions of the Willows area, the heads were plainly larger than they should be. In the case of individual pumping plants, which rarely discharge more than one or two cubic feet per second, checks necessarily are small. That waste of land goes with the large field ditches necessary in carrying large heads, and also that extravagant notions of use, and a greater waste when breaks occur with large heads, are sound arguments in favor of small heads, can not be doubted. Thoughtful consideration by irrigators and intelli- gent advice by public agencies in time will work out that relationship which best will serve both irrigators and the public. In the mean- time, it is very clear that irrigators should bear in mind the fact that the irrigation head should not be a constant quantity, but should be varied, where practicable, with the different soils found on nearly every farm. Dimensions and grades of alfalfa checks vary somewhat in the six sections of Sacramento Valley studied. Some square and rectangular checks are used in each section, but border or "strip" checks are most common, except on gravelly soils at Orland, where the most satisfac- tory check probably is one about 100 feet square, containing a little under one-fourth acre, and with each check having direct access to a field lateral to do away with carrying water to one check over another. The border checks range from 30 to 120 feet in width and from 60 to 1750 feet in length, the most usual width being from 30 to 50 feet and the most usual length from 400 to 700 feet. The grades of border checks range from 0.6 to 12 inches per 100 feet and average 3.6 inches per 100 feet. DESIRABLE MOISTURE PERCENTAGES FOR ALFALFA IN SACRAMENTO VALLEY SOILS AND THE EFFECT OF VARIATION IN SOIL MOISTURE ON RATES OF ALFALFA GROWTH In interpreting the results of the large number of soil-moisture determinations made at Davis and on Sacramento Valley alfalfa farms from 1913 to 1915, account has been taken of the moisture percentages found as related to the percentages at which the plants would wilt, and 292 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION also of the effect of the variation in those percentages on the growth of the alfalfa. The percentages at which the plants wilt, or the ■ ' wilting coefficients, ' ' have been computed on the basis of the experi- ments of Messrs. Briggs and Shantz of the Bureau of Plant Industry of the United States Department of Agriculture. 9 As indicated by these experiments, the wilting percentage may be stated to be the point below which moisture in the soil ceases to be available to the plants, or, at least, below which it is obtained only with great difficulty. Due largely to the difference in the size of the soil particles, plants will wilt in clay soils when there is still an amount of moisture that in sandy soils would be ample for all plant requirements. Determination of the wilting percentage of the soil was made for eight of the experimental plats at Davis, six of the experimental plats at Willows, and eleven of the Sacramento Valley alfalfa farms. Grouping the figures obtained, by soils, the average wilting percent- ages found were as follows : silt loams with fine sandy loam subsoils, 10.65 ; other silt loams, 13.12 ; clay loams, 14.21 ; clays, 13.06. In other words, it is necessary that at least the percentages of moisture indicated shall be present in these soils at all times in the growing season if the plants are to be kept from wilting. It must be noted, however, that in addition to these percentages of soil moisture that are necessary to prevent wilting, additional quan- tities must be present in order to produce satisfactory growth. Such additional amounts constitute the "available" moisture present in the soil. Obviously, it is impossible to disregard the numerous soil and climatic factors other than soil moisture that affect the yields of alfalfa, and then to expect the yields and moisture percentages to be consistent throughout. However, by grouping the yields above eight tons per acre, from six tons to eight tons per acre, and below six tons per acre, it is possible to approximate the best or "optimum" per- centage of available moisture over and above the amount necessary in each soil to prevent wilting. Assuming the yields over six tons per acre to have been produced on soil having at least as much as the ' ' optimum ' ' percentage of avail- able moisture, the data indicate that the "optimum" for Sacramento 9 U. S. Dept. Agr., Bureau of Plaut Industry Bulletin 230. The wilting per- centages, or "wilting coefficients," for the Sacramento Valley soils are based on the ' ' moisture equivalents ' ' of those soils, as determined in the laboratory of the Division of Soil Technology of the College of Agriculture of the University of California in the course of these investigations. It might be noted here that the moisture equivalents are the percentages of moisture retained in the soil after the soil has been subjected to a centrifugal force equal to 1000 times the force of gravity. IRRIGATION OF ALFALFA IN SACRAMENTO VALLEY 293 Valley conditions ranges between about 3 per cent and about 7 per cent and averages about 5 per cent above the wilting percentage. For one of the fields at Los Molinos and one of the plats at Davis, on both of -which an excess of irrigation water was applied, the average available percentage was 8.91, or well above the "optimum". On the other hand, the average percentage of available moisture on six ex- perimental plats at Willows, four plats at Davis, one field at Woodland, and one field at Willows, for which either the application or the ab- sorption of irrigation water was plainly deficient, was only 1.02, or well below the "optimum". The percentages of moisture that must be present in the various Sacramento Valley soils dealt with in order to prevent wilting are believed to be of value because they indicate to Sacramento Valley irrigators not only the difference between the clay or "heavy" soils and the loams and sandy soils as regards the amount of soil moisture needed to prevent wilting, but -also that for all of the soils the wilting percentage is higher than farmers usually suppose. If one could assume an absolutely dry soil it might be convenient for irrigators- to know that, as disclosed in the investigations, the amount of water necessary to supply the wilting percentage is ap- proximately the equivalent of about one and two-thirds inches of rainfall per foot of depth of soil in which the crop is growing, in the case of the silt loams with fine sandy loam subsoils, of about two inches in the case of the other silt loams, of about two and one-fourth inches in the case of the clay loams, and of two and three-fourths inches or more in the case of clays such as those found at Willows. 10 In other words, with an absolutely dry silt loam soil eight feet deep the first 16 inches of irrigation water would no more than supply the amount of moisture necessary to keep deep-rooting plants from wilt- ing; or, expressed still differently, with such a soil wholly devoid of moisture, the equivalent of a rainfall of two inches for each one foot depth of soil the crop utilizes would need to be supplied before the roots of the crop could begin to utilize the moisture. Fortunately an absolutely dry soil is rarely found in the Sacra- mento Valle}^, even at the end of the summer season, and except in very dry years the soils of the valley are not likely to begin the spring growing-season with less soil moisture than the wilting percentage. 10 The soil-moisture studies in connection with the clay soils at Willows dis- closed lower wilting percentages and lower capacities to absorb irrigation water than were to have been expected. It is not intended to discuss this technical phase of the subject in the present report, and conclusions for all Sacramento Valley clay soils can not and should not be drawn from the experience reported herein with the Tehama clays under investigation at Willows. 294 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The figures given should make it very plain that soils into which irrigation water percolates with difficulty should be watched very care- fully at depths from four to six feet below the surface. The ex- perience of the field investigators at Willows indicated that this care is especially necessary even early in the summer in order to insure that an adequate irrigation supply shall replace the moisture absorbed from the winter rainfall after that has been utilized. 11 11 What is said in the text regarding desirable moisture percentages for Sacramento Valley soils growing alfalfa considers the matter only from the standpoint of the total annual yields of hay. It is obvious, however, that the annual yields are results of conditions that vary from day to day and from week to week. For instance, considering the moisture factor only, annual differences in yield were results of the daily and weekly differences due to daily and weekly variations in soil moisture. The data collected have been studied with reference to the effect of these changing moisture percentages on the seasonal rates of growth, but as no data were collected to indicate daily or even weekly variations in rates of growth, making it necessary to rely on average rates of growth between cuttings, such deductions as were suggested in the study have not seemed sufficiently conclusive to warrant their presentation. It is, however, possible to say that where the moisture percentage was found to fall below the wilting point there was also found a definite falling off in the rate of alfalfa growth.