i8 



Journal of Agricultural Research 



Vol. XIII. No. I 



Table VII. — Number of acre-inches and percentage of the amount of water applied in 

 each irrigation which was retained by the upper 6 feet and the upper 12 feet of soil, Uni- 

 versity of California farm, Davis, Cal. Averages for 1913, 1914, 191 5 



For convenience in referring to the plots, letters are used instead of the numbers in parentheses. The 

 latter were used on page 10, California Department of Engineering Bulletin 3. 



6 Borings were made only to a depth of 6 feet in plots B, C, and D. 



« Group averages obtained by giving plots percentages and weights proportional to quantities of 

 water applied. 



The amounts of water held by each foot of soil before and after 

 irrigation and the average increases which were found for the various 

 treatments are set forth in Table VII I . For ease of comparison these data 

 are presented graphically in figures 7 to 12. The water contents of 

 plots B and D are compared in figure 7. The soil of plot B being finer in 

 texture than that of plot D, especially below 3 feet, accounts for the 

 higher water content both before and after irrigation. Variation in 

 the soil of plot B is probably the cause of an apparent discrepancy in 

 the relative amounts of water accounted for. The comparison of plots 

 C and D presented in figure 8 indicates that plot C became drier before 

 irrigation than did plot D, which accounts for the greater amount of 

 w^ater being retained by plot C since each plot contained about the same 

 quantity after irrigation. Figure 9 indicates that the upper 6 feet of 

 plots E and G were moistened to their full capillary capacity. It is 

 likely that the clay-loam stratum of the seventh foot in plot G by retard- 

 ing downward movement caused some gravitational water to be held 

 in the fifth and sixth foot section till the time of sampling. The effect 

 of the large irrigations of plot G is evident in the great difference between 

 the moisture contained, before and after irrigation, in the third to the 

 sixth foot sections. Figure 10 shows that the 12-inch irrigations of 

 plot G caused slightly greater increases than the 9-inch applications of 

 plot F in the second to seventh foot, below which the increases were very 

 irregular. 



