116 AGRICULTURAL ENGINEERING 



plants strike deep and are thus able to draw moisture from 

 a larger volume of the soil. 



Character of the Soil. The amount of water required is 

 dependent largely upon the character of the soil; thus the 

 soil may be so open or porous as to permit a rather large loss 

 of moisture by seepage. The character of the soil influences 

 to a rather large extent the effectiveness of the soil mulch 

 which conserves the moisture in the soil, which is to be 

 described later. 



Character of the Subsoil. The character of the subsoil 

 is a factor in determining the amount of water required by 

 the plant, for an open subsoil will be the means of a great loss 

 of moisture by percolation downward. 



Effect of Cultivation. Cultivation for maintaining a soil 

 mulch will influence to a large extent the amount of moisture 

 required for most satisfactory plant growth. In dry-farming 

 localities, as well as elsewhere, moisture is conserved by keep- 

 ing a dust mulch, or fine layer of soil, over the surface. Much 

 of the moisture in the soil available for the growth of plants 

 may be retained in this way from one wet season through a 

 dry season. After a rain or an application of irrigating water, 

 it is customary to cultivate the soil as soon as practical in 

 order to form this mulch. 



Closeness of Planting. A dense, heavy crop that shades 

 the ground will check the loss of moisture by evaporation. 

 Thus it is customary to irrigate grain crops most thoroughly 

 at the time when they are heavy enough to shade the ground. 



Character of Rainfall. The character of the rainfall is an 

 important factor in fixing the duty of water; one heavy rain 

 which penetrates the soil to a considerable depth is more use- 

 ful than several light rains which are quickly evaporated. 

 Thus localities which have a wet season are often able to 



