﻿WATER UTILIZATION BY SPRING WHEAT. 21 



The third foot section of soil, when compared with the second, 

 shows a material reduction in the full use of water on plats A and 

 B. In this section the soil has been filled to capacity and all the 

 water used (F) only about 25 per cent of the time. This is ac- 

 counted for by a marked increase in the proportion of cases when no 

 available water was present (OD). There is a slight reduction in 

 the percentage of time the available water was only partly used 

 (PW). Little change is shown in the percentage of cases when the 

 soil was only partly filled with water and all available water used 

 (PD). The reduction in the number of times the soil moisture was 

 reduced but not exhausted (PW) probably represents the fewer num- 

 ber of times that rains near harvest affected the water content of the 

 soil to this depth. 



Summing up the results for this foot section, the soil was dry at 

 harvest (F, PD, and OD) 93 per cent of the time on both plats 

 A and B. In the remaining 7 per cent of the cases the water content 

 of the soil was reduced but not exhausted (PW). Thus, it is found 

 that there is no great difference in the first 3 feet of soil in the per- 

 centage of the time that harvest finds them without available water, 

 but that the actual use of water is progressively less as the distance 

 from the surface increases, because of the limitation in the extent to 

 which the soil is filled with moisture. 



In the fourth foot section of plats A and B the soil has been filled 

 with water and all the water used (F) less than 10 per cent of the 

 time, partly filled with water and all used (PD) in about 25 per cent 

 of the cases, and it has been dry all the season (OD) about 55 per cent 

 of the time. There is little change in the proportion of cases where 

 the moisture has been reduced but not exhausted (PW). A few cases 

 appear on each plat where available water was not reduced (OW) . 



The percentage of the time when no water was available at harvest 

 remains nearly as high as in the upper 3 feet of soil. But the great 

 proportion of the time that this foot section has been dry or only 

 partly filled with water makes it far less valuable than the third 

 section in supplying moisture to the wheat crop. 



Below the fourth foot available water has been present in the soil 

 of these plats in only one-third of the cases. Full use practically 

 ceases, and the number of times the soil has been partly filled with 

 water and all of it used is reduced. On the other hand, the propor- 

 tion of the time no use is made of available water rises. 



Considering the fact that the soil at depths below 4 feet has been 

 moist only infrequently, that the quantity of moisture held when the 

 soil is filled to capacity is not great, and that the wheat crop has been 

 able to use all the available water present only about half the time in 

 the fifth foot and one-third of the time in the sixth foot the conclu- 

 sion must be drawn that the fifth and sixth foot sections of soil on 

 land continuously cropped to wheat are generally without value so 

 far as crop production is concerned. 



In plats A and B it was found that the limitation of the depth to 

 which water was used in the upper sections at least depended so much 

 upon the depth to which moisture was present in the soil that other 

 factors were obscured. In the C or D plat the soil has been wet to a 

 greater depth, as a rule, and it has been possible to compare the indi- 



