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 bj 7 
precipitation. Eeduction 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. 
