Apr. I, 1918 



Capacities of Soils for Irrigation Water 



irrigation tract at the University farm is very uniform in texture; the 

 third- to eighth-foot sections consist of fine sandy loam which is pock- 

 eted at irregular interv^als with coarse sand and clay loam, below which 

 is a heavy clay loam extending from 9 to 20 feet or more below the sur- 

 face. The Tehema clay of the Willows tract is impervious to water and 

 is very hard when dry. 



Strictly speaking, the quantities of water accounted for, as given in 

 the following pages, except as noted in the sixth and seventh columns 

 of Table II, are a little low, since they do not include the water used by 

 the plant immediately after irrigation. Upon the basis of experiments 

 previously conducted at Davis (6), a total of approximately 1.08 inches 

 of water was evaporated and used by the alfalfa during the first four 



04 OS 



0£PTH OFirATCfi IN IHCMCS 



Fio. 1. — Diagram for detennining the depth of irrigation water in inches necessary to add a given percent- 

 age of moisture to i foot of soil. 



days after irrigation, the average time which elapsed between irrigation 

 and the collecting of soil samples for moisture determinations. Including 

 these probable evaporation losses, the total quantities and percentages 

 of water accounted for are given in the sixth and seventh columns of 

 Table II. When the average depth of irrigation water applied was 

 small, as in the clay soils, the percentage loss of water during the first 

 four days after irrigation was relatively high ; consequently the percent- 

 ages accounted for as given in the seventh column of Table II are rela- 

 tively high for heavy soils, varying from 41 .5 in the silt-loam soils to 69.4 

 in the clay soils. However, since practical considerations involved in 

 irrigation farming demand that the v/ater supply of the plant be furnished 

 at different periods, the quantities of water stored in the soil by each 

 irrigation, as indicated in column 5 of Table II (not including evapora- 

 tion) and in Tables III and IV, may well be considered in each case 

 representative of the effective irrigation. Moreover, since the studies 



