248 



SOIL PHYSICS AND MANAGEMENT 



within the limit of the root zone for plants under arid conditions. 

 This varies from eight to ten feet or more in depth. Experiments 

 in Utah showed as much as 95^ per cent of the water which fell 

 as rain and snow during the winter was found stored in the first 

 eight feet of soil in the spring. Atkinson found that at the Mon- 

 tana Station soil which contained 7.7 per cent of moisture in the 

 fall contained 11.5 per cent in the spring and after proper summer 

 tillage contained 11 per cent in the fall. The following tahle shows 

 the amount of water that may he stored in the soil during the 

 winter : 



Percentage of Water in Each Foot of Soil to a Depth of Eight Feel 8 



It will he noted that the increase of moisture amounted to eight 

 inches for the eight feet of soil. Water storage in a soil is impos- 

 sible when a crop of weeds is growing. 



System of Cropping. There can be no continuous cropping 

 in dry-land agriculture as in humid regions, because the rain- 

 fall is not usually sufficient to grow two crops in succession. 

 However, if the rainfall of two seasons can be used for growing a 

 single crop, profitable results may be obtained. The conservation 

 of this moisture from one season to the next is the most important 

 problem in this kind of agriculture. The possibilities of raising 

 grain under dry farming methods are seen in figures 108, 109 

 and 110. 



Continuous Cropping vs. After Fallow. Average Remits for All Years Tested, 

 Montana Station" 1 ([iushcls Per Acre) 



