THE CONTROL OF SOIL MOISTURE 269 



of run-off and percolation, then, is first, to have a loose, 

 open structure of soil in order to facilitate ready entrance 

 of the water; and secondly, to promote and encourage 

 a physical condition of soil which provides high capillary 

 capacity. Drainage, lime, humus, and good tillage en- 

 courage granulation, which has so much to do with the 

 proper entrance of water into the soil and its proper 

 handling and utilization therein. The benefits of drain- 

 age are felt only when free water, superavailable to 

 plants, becomes present. Its quick removal, therefore, 

 not only betters the physical condition of the soil, but 

 also aids in the maintenance of the optimum moisture 

 conditions for the plants. 



Fall and early spring plowing is always recommended 

 as a means of increasing the moisture capacity of the 

 soil, particularly where organic matter is well supplied. 

 It provides a deep soil, and should establish the best 

 conditions for the storage of moisture, as well as food, 

 for the plant. If organic matter is not supplied, deep 

 plowing is not advisable on light sandy soil ; but on 

 clay soil it is beneficial because of the loosening and granu- 

 lating effect. Fall plowing in particular is to be recom- 

 mended for such soil, as the loose condition produced 

 facilitates the entrance of surface water while the granu- 

 lation that the soil undergoes during the winter increases 

 its water-holding power. A soil in excellent physical 

 condition may contain considerably more water than 

 the soil of the same texture but in poor tilth, and yet 

 present better conditions for crop growth. Where fall 

 plowing cannot be done, early spring plowing is the next 

 best procedure. 



188. Evaporation losses. Evaporation of soil water 

 takes place almost entirely at the surface, exceptions 



