20 



Journal of Agricultural Research 



Vol. Xin, No. I 



The upper 6 feet of the water-content curves in figure 1 1 plotted from 

 the averages in Table VIII are based on 294 borings and 1,764 moisture 

 determinations; the section from 7 to 9 feet is based upon 120 borings 

 and 360 single observations; and the depth from 9 to 12 feet represents 

 averages of 48 borings and 144 moisture determinations. The curves 

 for the upper 6 feet of plot H presented in figure 12 are based on 56 

 borings and 336 single observations; the section from 7 to 9 feet on 40 

 borings and 120 single determinations; and for the depth from 10 to 12 

 feet on 16 borings and 48 single moisture tests. 



-PLOT a C^-6' UmiSATIONS) 

 .PLOT O (4-&- l/^R!GATlOHi) 

 ,MOISTUftC £Q.UIV>^LC^T 



Fig. 7. — Graphs showing the comparison of water content before and after irrigation, moisture equivalent, 

 and pore space of soils of plots B and D, Davis, Cal. Each water-content curve in plot B is the average 

 of 14 borings; in plot D, of 28 borings. 



MAXIMUM CAPIIvLARY CAPACITY OF DISTURBED SOILS AND SOILS IN PLACE 



That the results of standard laboratory determinations of maximum 

 capacity of soils do not accurately represent capillary capacities of soils 

 in place is generally recognized. Widtsoe (72) determined the maximum 

 capillary capacity of a soil in place by studying three columns i foot, 

 2 feet, and 3 feet long, respectively. The samples were taken by driving 

 iron cylinders into the soil, thus getting it almost in its natural condition. 

 By means of three independent linear equations, the efl'ect of the special 

 "lifting power" exerted by the end of each soil column was eUminated. 

 It was found by this procedure that 28.4 per cent of the total water held 

 in the i-foot column was retained by this special force, which does not 

 exist in ordinary field soils. The maximum capillary capacity thus 



