﻿20 BULLETIN 1139, U. S. DEPARTMENT OF AGR I CULTURE. 



The differences in the number of cases in the different foot sec- 

 tions are in a Large measure the result of the limitation of sampling- 

 due to the limitation of depth of feeding in certain soils. If the 

 samples had ail been taken to a depth great enough to make the 

 table entirely symmetrical, the condition of the sixth foot would have 

 been expressed by the symbols OW or OD in nearly all of the 63 

 cases when determinations were made in the first foot section but not 

 in the sixth. 



Consideration of the table will be confined largely to the portion 

 where the results are expressed as percentages. The most striking 

 feature of the table is the closeness with which plats A and B ap- 

 proximate each other. In the first foot of soil both were filled to 

 capacity, and all of the water was used about three-fourths of the 

 time. About 10 per cent of the time the soil was not entirely filled 

 with water at any time during the growing season, but all available 

 water was used. In only 1 per cent of the time, which represents 

 the year 1915 at North Platte, was the soil filled with water at 

 harvest. There has never been a case where no available water was 

 present in the first foot during the growing season. In one year, 

 1911, at Belle Fourche, very little available moisture was present in 

 the first foot of plats A and B. This j-ear was necessarily omitted 

 in Table 1, as the soil was so dry that the wheat did not come up. 



Summing up the results for the first foot, it is found by adding the 

 percentages under the symbol PD to those under the symbol F that 

 the available water in both plats A and B was entirely depleted 

 at harvest in 89 per cent of the cases studied; the water content was 

 reduced but not entirely exhausted (the condition represented by 

 the symbol PW) in 10 per cent of the cases; and the soil was still 

 full of water at harvest time (classed as the condition OW) in 1 per 

 cent of the cases. 



The second foot section of plats A and B, when compared with 

 the first, shows a sharp reduction in the number of times full use 

 of water was made (F). This is accounted for by the great increase 

 in the percentage of cases when the soil was only partly filled with 

 moisture and all of it used (PD) and in the appearance of a few 

 cases where the soil was dry all the season (OD) . The proportion of 

 the time that moisture present in the soil was only partly used (PW) 

 remains nearly constant. 



Summing up the results for the second foot section, it is found 

 that it was dry at harvest 89 per cent of the time on plat A and 87 

 per cent of the time on plat B. This is the sum of the percentages 

 under symbols F, PD, and OD. The moisture content was reduced 

 but not exhausted in 10 per cent of the cases on plat A and in 13 per 

 cent of the cases on plat B. This condition is represented by the 

 symbol PW. There was only 1 per cent of the time on plat A when 

 the moisture content of the soil was not reduced when available 

 moisture was present. This is the condition shown by the symbol 

 OW. All of the available water in the second foot of the two 

 plats was removed practically the same proportion of the time as 

 in the first foot. The aggregate quantity of water obtained by the 

 wheat crop from the second foot must have been considerably less 

 than that obtained from the first foot, as it has been filled with water 

 less frequently. 



