SOIL WATER 



101 



ground from the sun and wind. Protections of this kind 

 are called mulches. They are most frequently used around 

 trees, vines and shrubs. It is impracticable to use them 

 extensively on growing crops. 



It was also found that soil water was not readily evapo- 

 rated where the top of the soil was kept stirred, so that 

 the little capillary tubes by which the soil water reaches 

 the surface were broken and the sunshine and air were kept 

 from the under part of the soil by a layer of finely divided 

 soil mulch. When the surface of the soil is thoroughly 

 stirred or cultivated the particles are separated so far 

 apart that the water cannot pass from one grain to an- 

 other, and so is retained in the under layer ready for the 

 plant roots. Thorough tillage of agricultural crops is 

 perhaps the best way to assure the plants sufficient 



moisture in regions subject to ^____ 



droughts. 



In some parts of the arid 

 region of the United States dry 

 farming is practiced. The soil 

 is deeply plowed and the plow 

 often followed by a bevel wheel 

 roller called a soil packer, in 

 order to pack the under soil or 

 subsoil so that the air cannot 

 circulate through it and dry 

 out the upper soil. The sur- 

 face soil is then most thoroughly 

 cultivated so as to make as per- 

 fect a soil mulch as possible. 

 Thus, whatever moisture falls is kept from seeping below 

 the reach of the plant roots and from evaporating from 

 the surface. In this kind of farming the aim is to use 

 more than one year's moisture in growing a crop. 



KAFFIR CORN. 

 A plant suitable for dry farming. 



