﻿WATER UTILIZATION BY SPRING WHEAT. 27 



quantity and character of the precipitation than by the storage 

 capacity of the soil. 



Available water, when present in the soil, is removed with about 

 the same degree of frequency from each of the first 4 feet. The 

 aggregate quantity of water contributed by each foot section be- 

 comes progressively less with increasing distance from the surface, 

 both because each successive foot section is less frequently filled with 

 water and because the quantity of available water that may be held 

 in each successive unit is less. The fifth and sixth foot sections hold 

 still less available water, and the full use of their limited capacity is 

 not frequent. They contribute very little to the total quantity of 

 water used by the crop, but under certain conditions this contribution 

 may be important. 



In about 90 per cent of the years covered by these investigations 

 the soil within the zone of normal root development was dry at 

 harvest time. 



The utilization of a large soil mass is not essential to a high 

 yield. The yield depends more upon the maintenance of a constant 

 supply of available moisture to the depth at which it can be easily 

 obtained than upon the mass of soil involved. 



