LOSS OF SOIL MOISTURE 



75 



(Fig. 28). Later, metal wheels or disks were substituted as fol- 

 lowers. These tools are used until the ridge has been partly worked 

 down, then the ordinary shovel cultivator. 



Reasons for Intertillage. Intertillage is so universal for cer- 

 tain crops that we scarcely stop to ask the reason, assuming it neces- 

 sary for growth. 



The reasons differ somewhat, but the important reasons seem to 

 be (1) to conserve moisture and (2) to destroy weeds. In addition, 

 cultivation probably helps in many cases in freeing some plant food ; 

 also a well cultivated surface will probably take up more water, in 



FIG. 28. Two-row cultivator for listed corn at work. 



the case of sudden heavy rainfall, than an uncultivated surface. The 

 first two reasons, namely, conservation of moisture and destruction 

 of weeds, are the points to give most attention. 



Loss of Soil Moisture. As fast as moisture evaporates from the 

 surface, more water moves up from below. This is called the capil- 

 lary rise of water, since its upward movement against gravity in the 

 very small spaces between soil particles is similar to the rise of a 

 liquid in a capillary tube. When these small "capillary " spaces are 

 broken up, as by cultivation, the upward movement can not reach the 

 surface, and water loss by evaporation decreases. Hence in a bare 

 soil, without cultivation, water loss is large, and it has been demon- 



