﻿WATER UTILIZATION BY SPRING WHEAT. 25 



where the character of the soil permits 'easy penetration of water 

 and plant roots, the natural zone of development of wheat roots is 

 the first 4 feet of soil. In many years, particularly on plats A and B, 

 lack of moisture prohibits root growth to that depth, but where 

 moisture is present in the first 4 feet of soil the evidence at hand 

 points to a nearly uniform utilization of moisture within these 4 

 feet. The use of water below the fourth foot section of soil depends 

 primarily upon the character of the season. In years when moisture 

 is present in all 6 feet of soil, little or no use of water below the 

 fourth foot is shown if there is at all times a supply of available 

 moisture present in the first 4 feet. Development of any consider- 

 able number of roots in the fifth and sixth foot sections of soil 

 seems to be made only under stress of a shortage of moisture, 

 either temporary or continued. The extent to which the moisture 

 in these depths is used depends largely upon the length of time 

 that the crop suffers for moisture without drying up or ripening 

 prematurely. The complete utilization of water at these depths 

 seems to require a fair growth of crop and an extended period of 

 time when the crop needs water but does not actually die or come 

 to a forced maturity. The quantity of available moisture held in 

 the fifth and sixth foot sections of soil is usually small, and its 

 complete or nearly complete utilization necessitates conditions so 

 severe that the yield of the crop is almost always seriously com- 

 promised. So far as actual benefit to the crop in ordinary years 

 is concerned, the moisture held in the soil below the fourth foot is 

 of no importance. In a few years the moisture at these lower depths 

 has maintained life in a crop and has enabled it to take advantage 

 of favorable conditions later in the season. 



In exceptionally severe years, such as 1911 at Belle Fourche and 

 North Platte, the demands for moisture by the wheat crop have been 

 so excessive that the plants dried up without feeding deeply because the 

 roots could not extend themselves rapidly enough to obtain a supply of 

 moisture sufficient to maintain life. The limitation of root develop- 

 ment was caused not by lack of water or by lack of demand for water, 

 but by a demand for water so great that it could not be met. This 

 condition is rare, but an approximation of it late in the life of the 

 crop has often been responsible for a forced ripening without the 

 roots reaching their fullest development. 



The fact that, moisture is normally exhausted in the first 4 feet of 

 soil does not indicate that the moisture is exhausted simultaneously 

 in the different foot sections. In general, the several foot sections 

 are reduced to the minimum point successively in the order of their 

 distance from the surface. There is very little margin between the 

 first and second foot sections of soil in the time at which they be- 

 come dry. The principal reason for this is doubtless that the roots 

 become well disseminated through at least this much soil before the 

 wheat reaches a stage of growth where its demands for moisture 

 become heavy. There is, in addition, the fact that the exhaustion of 

 the moisture content of the first foot of soil is frequently delayed by 

 precipitation. Seduction of soil moisture in the third and fourth 

 foot sections commences before the moisture in the first 2 feet of soil 

 is exhausted. However, the minimum point is reached distinctly 

 later in the third foot section than in the second and distinctly later 

 in the fourth than in the third. 



