86 



WATER IN SOILS 



The process by which hygroscopic moisture moves is called 

 thermal movement. This is because the internal evaporation and 

 condensation of such moisture in the soil is due to the difference 

 in heat. More heat causes evaporation and less heat causes con- 

 densation from the soil air. 



Water-holding Power of Soils. No reference is here intended 

 to the capacity of a soil for free water. The only form of wa,ter 

 that is valuable to plants is that in capillary condition. The more 

 capillary water a soil can hold the better it can produce crops. 



FIG. 66. Placing dynamite and fuse in a drill hole two feet deep. The explosion loosens 

 the subsoil for the. roots of trees and other plants. They find the moisture conditions much 

 better after such treatment. (New Jersey Station.) 



It is therefore highly important that a farmer or gardener should 

 endeavor to increase the capacity of his soils for holding capillary 

 water. This he can do in a number of ways : 



1. Deep tillage will greatly increase the air space and allow 

 the soil to hold more capillary moisture (Fig. 66). Portions of 

 the soil which are not stirred by the plow become so closely packed 

 together that the capacity for capillary films is greatly reduced. 

 Soil grains gather together in compound particles, and if this con- 

 dition is prevalent in any soil the result may be that of having 

 very coarse particles. Coarse soils hold less moisture. Tillage, 



