﻿24 BULLETIN li::.», IT. S. DEPARTMENT OF AGRICULTURE. 



Certainly the greater quantity of moisture stored by either method 

 in any section is oot enough to counterbalance other factors such as 

 timeliness of work, control of -weeds, and prevention of soil blbwing. 



Plat C or D has been markedly superior to the other two plats in 

 moisture storage at all stations except those with a limited water- 

 storage capacity. At Edgeley, it will he remembered, the. soil is so 

 shallow that practically all of it has been lilled to capacity for all 

 methods of cultivation each year between harvest and seeding: con- 

 sequently, little difference between methods has existed. At some. 

 other stations, such as Archer and Ardmore, the difference in favor of 

 plat C or D has been small. The superiority of C or D over A and B 

 in individual years has depended upon the quantity of rainfall as 

 well as the character of the soil. The demand of the wheat crop for 

 moisture differs in the several portions of the Plains, 7 and a given 

 quantity of stored water may be of more value at one station than 

 another. When translated into bushels of yield 4 inches of water 

 stored at Assinniboine would probably be much more valuable than 

 the same quantity of water at Amarillo. The superiority of plat 

 C or D over the other plats in conserving moisture must be con- 

 sidered in terms of increase in bushels per acre to determine the 

 value of fallowing as a farm practice. 



Alternate cropping and summer fallowing practiced in these 

 experiments has in all but the driest years stored moisture in the 

 entire zone of natural development of the roots of the wheat crop. 

 It is evident from this that any extension of the fallow period for 

 the purpose of increasing the quantity of moisture stored would not 

 often be effective in increasing the yields of wheat. The more likely 

 result in most years would be the storage of moisture at a depth 

 where its recovery by the wheat crop would be extremely doubtful. 



The three plats taken together indicate that moisture is the con- 

 trolling factor in crop production in the Great Plains and that differ- 

 ences in yield generally are due to differences in the water supply. 

 Plats A and B have produced yields almost or quite equal to those 

 on plat C or D in years when they have contained the same quantity 

 of water. 



GENERAL CONCLUSIONS. 



Under dry-farming conditions there is present in the soil no 

 ground water or other source of free water. Below the zone of a 

 few feet near the surface, which the present study shows may be 

 wetted and dried during the cycle from harvest to harvest, the soil 

 is either dry or does not contain water above its field carrying 

 capacity. Under these conditions no water moves upward through 

 appreciable distances to replace the water removed by the roots. 

 Water is supplied to the roots only by such part of the soil as they 

 occupy, and only that part of the soil suffers exhaustion or reduction 

 of its water content. 



The development of the roots of the wheat plant is indicated by 

 the depth and extent to which the soil water is used. The usual 

 depth of development is indicated by the results given in detail in 

 Table 1 and summarized in Table 2. It appears that at stations 



7 Cole. John 8.. and Mathews, O. R. Use of water by spring wheat on the Great Plains, 

 r. S. Ivpt. Agr. Bui. 1004, 34 p., 10 flg. 10L*:i. 



