Apr. I, 1918 



Capacities of Soils for Irrigation Water 



13 



these soils is in all probability very high, to judge from their mechanical 

 analysis, which showed 24.54 per cent of total sands, 40 per cent of silt, 

 and 34.84 per cent of clay. Yet the quantities of water found in them 

 both before and after irrigation were extremely low. This condition 

 is especially evident when the results are recorded in percentages rather 

 than in inches per foot, since the high volume weights increase their 

 water content relatively when reported upon the latter basis. 



The observations made upon clay soils are presented in Table IV and 

 figures 5 and 6. Figure 5 is based upon 86 six-foot borings, making 516 

 moisture determinations, and figure 6 contains averages of 568 borings 



Fig. 5. — Graphs of the water content before and after irrigation, moisture equivalent, and pore space of 

 clay soils. Each water-content curve is the average of 43 borings. 



in which 3,408 moisture determinations were made. Table IV reveals 

 at a glance the striking fact that only the surface foot of soil was appre- 

 ciably moistened by the irrigation v/ater. It is doubtful if the capillary 

 power of the surface foot was entirely satisfied ; yet it held after irrigation 

 3.06 inches of water, or enough to fill 64.3 per cent of its pore space. 

 The sixth foot, which was kept moist by the ground-water table, con- 

 tained no gravitational water, but 86 per cent of its pore space was 

 occupied by capillary water, leaving only 16 per cent of the 4.71 inches 

 of pore space per foot of soil for air, or only two-thirds of one inch in 

 twelve. 



