152 DRY-FARMING 
farm sections, where grain is harvested by the 
“header”? method. 
A special case of shading is the 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 beneficially. 
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 easily will the 
movement of the soil-moisture proceed. If by any 
means a iayer of the soil is so loosened as to reduce 
the number of points of contact, the movement of the 
soil-moisture is correspondingly 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 opened, a certain 
number of passengers can pass through each minute; 
