Apr. I, 1918 



Capacities of Soils for Irrigation Water 



15 



Table IV. — Water content before and after irrigation, the moisture equivalent and the 

 pore space of tlie soils of typical alfalfa farms in Sacramento Valley, California, 

 igij-igij. Averages for each foot of soil to a depth of 6 feet — Continued 



CLAY SOILS, 1915 <* 



Tract, location, and time of sampling. 



Num- 

 ber 

 of 

 bor- 

 ings 

 for 

 soil 

 sam- 

 ples. 



Water content. 



Mois 

 ture 

 equiv- 

 alent 



in 

 acre- 

 inches 

 per 

 acre- 

 foot 

 of soil 



Pore- 

 space 

 acre- 

 inches 

 per 

 acre- 

 foot 

 of soil, 

 memm 



Depth at which samples were taken, inches. 



Plots 3 and 4, Willows experimental tract: 



Before irrigation 



After irrigation 



Increase 



Plots 6 and 7, Willows experimental tract: 



Before irrigation 



After irrigation 



Increase 



Plots II and 12, Willows experimental tract: 



Before irrigation 



After irrigation 



Increase 



Averages: 



Before irrigation 



After irrigation 



Increase 



140 

 140 



48 



I. 71 



2. 40 



.69 



1.78 

 2.97 



1-45 

 2.91 

 1.46 



1.6s 

 2. 76 



2. 10 



2.18 



.08 



2-31 



2.62 



■31 



1.97 



2-52 



•5S 



2.41 



2.42 



.01 



2.67 

 2.79 



2.38 

 2. 50 



2-57 

 .08 



2.99 



3.06 



.07 



2.62 

 2-73 



2.87 

 2.84 

 -•03 



3-36 

 3-38 



2-93 



3.06 



•13 



3-05 

 3-09 



3-96 



3-99 



.03 



4-95 

 4-8s 



4.08 



4-33 

 4.28 

 -•03 



4.78 



o The plan of sampling the upper 2 feet of the clay soils was in 1915 changed from one sample in the middle 

 of each fooW-section to one in the middle of each 8-inch section, thns giving three samples in the upper 2 

 feet. The sixth foot was not sampled in 1915. These data are presented graphically in figures 5 and 6. 



The unusual conditions which were encountered in the Willows area 

 during 1914 seemed to warrant further work upon this type of soil, and 

 in 1 91 5 twelve 2-inch, eight 4-inch, and four 6-inch irrigations were 

 given to plots 3 and 4, 6 and 7, and 1 1 and 12, respectively, of the Willows 

 experimental tract. 



Three samples were taken in the upper 2 feet of soil — that is, one rep- 

 resenting each 8-inch section.^ The relatively small individual increases 

 observed in plots 3 and 4, as compared to those in plots 6 and 7, are 

 probably due in part to differences in soil compactness,^ but the smaller 

 unit application of water was in all probability the chief controlling 

 factor. The total seasonal increase in the different plots — that is, the 

 unit increase multiplied by the number of irrigations as shown in Table 

 V — is relatively higher in plots 3 and 4. 



1 In examining the water contents presented in Table IV, it must be remembered that the results pre- 

 sented in the three columns at the reader's left are at the rate of the various numbers of acre-inches per acre- 

 foot of soil, and must therefore be multiplied by 8/1 2 to get the actual increase in each of the individual 8-inch 

 sections. This has been taken into account in the calculations of quantities of water accounted for, as pre- 

 sented at the bottom of Table II. 



2 The soil of plots 6 and 7 is less compact than that of the other plots. (See Table I. ) 



