152 DRY-FARMING 



farm sections, where grain is harvested by the 

 "header" method. 



A special case of shading is tlie mulching of land 

 with straw or other barnyard litter, or with leaves, 

 as in the forest. Such mulching reduces evaporation, 

 but only in part, because of its shading action, since 

 it acts also as a loose top layer of soil matter breaking 

 communication with the lower soil layers. 



Whenever the soil is carefully stirred, as will be 

 described, the value of shading as a means of checking 

 evaporation disappears almost entirely. It is only 

 with soils which are tolerably moist at the surface 

 that shading acts beneficiall}'. 



The effect of tillage 



Capillary soil-moisture moves from particle to 

 particle until the surface is reached. The closer the 

 soil grains are packed together, the greater the num- 

 ber of points of contact, and the more easih' will the 

 movement of the soil-moisture proceed. If by any 

 means a layer of the soil is so loosened as to reduce 

 the number of points of contact, the movement of the 

 soil-moisture is corresj^ondinglj' hindered. The pro- 

 cess is somewhat similar to the experience in large 

 railway stations. Just before train time a great 

 crowd of people is gathered outside of the gates ready 

 to show their tickets. If one gate is oj^ened, a certain 

 number of passengers can pass through each minute ; 



