422 Irrigation and Drainage 



away. It is in this manner that coarse, sandy soils 

 are impoverished, and their lack of productiveness 

 is often due quite as much to too thorough ventilation 

 as to too complete drainage ; and in handling these 

 soils the utmost care should be exercised to keep 

 the content of humus high, the moisture plenty, and 

 the winds from drifting away the finest dust particles, 

 because all of these tend to close up the pores, giving 

 the soil a texture which diminishes the amount of 

 ventilation. 



DRAINAGE INCREASES THE AVAILABLE SUPPLY OF 

 SOIL MOISTURE FOR CROPS 



When soils are poorly drained during spring and 

 early summer, the root system of the various crops 

 is forced to develop near the surface, and if this is 

 the case until the demands for moisture become large, 

 the soil in which the roots are confined becomes very 

 dry, because capillarity brings the water up from 

 below too slowly to meet the demand. 



It is a familiar fact that a damp cloth is much 

 better to remove water from the floor than a dry one, 

 and the same is true of soils ; water rises by capil- 

 larity in them when quite moist much faster than 

 when they become dry, and so it is a matter of the 

 greatest moment to keep the surface soil, beneath the 

 mulch, as damp as the best conditions for growth 

 will permit. When the deeper soil in the spring and 

 early summer is well drained, and the roots of the 

 crop penetrate it, they not only find themselves closer 



