SOIL WATER 91 



passing upward has been stopped. That is why 

 fishermen hunt for earthworms beneath stones, 

 when the weather is very dry. A layer of small 

 flat rocks scattered over the surface of the ground 

 would prevent a large part of the film water from 

 escaping, were it practicable. The woodpile 

 offers another illustration, for the soil is always 

 moist beneath the layer of chips, showing that evap- 

 oration has been checked. But a layer of straw 

 does just as well and is easier to apply. 



Any material that is spread upon the soil to stop 

 up the mouths of the water tubes and shade the 

 surface from the sun, thus preventing the loss of 

 soil water, is called a mulch. The most effective 

 and practicable mulches are coarse hay, straw, and 

 farm manures ; not only because they are easy to 

 apply, but also because they benefit the soil in other 

 ways, chiefly through the humus that they add. 

 Occasionally other materials are used to mulch the 

 soil, as leaves, straw waste, coal ashes, sea-weed. 

 Mulching to save soil water is rarely practised in 

 growing common farm crops. Small fruits, espe- 

 cially the strawberry, currant and gooseberry and 

 also, to a slight extent, the tree fruits, are frequently 

 mulched with these materials. 



The Soil Mulch. The most practicable mulch 

 in general farming is made of loose, dry soil. This 

 is obtained by stirring the surface of the soil with 

 the implements of tillage, as the plow, harrow and 

 cultivator. Stirring the soil makes it much looser. 

 The pores are broken. Water can creep from one 

 soil grain to another only when the grains are close 

 together when the soil is compact. Stirring the 

 soil spreads the grains so far apart that water can- 

 not pass from one grain to another, or but very 

 slowly. So it comes no further than the mouths 



