' Irrigation and Drainage 145 
plants is prevented. Drainage, which gradually removes 
these salts, is the only method of reclining 4 alkali land 
permanently. Much land that is 
at present valueless on account of 
its high alkali-content would be 
of excellent quality were its excess 
salts removed. In fact, some of 
the highest yields of sugar-beets 
are obtained on land thus re- 
claimed. 
——a -* 
<= 
Effects of drainage. 
The drainage of wet land im- 
proves it in many indirect, as well Fre. 22. — Drainage 
as direct, ways. Lowering the Hayeeete ae eal 
water-table gives plants a larger 
zone from which their roots can draw plant-food and 
moisture. This lessens the need of fertilizers and the 
susceptibility to drought. The increased aération of the 
soil resulting from drainage promotes the growth of 
desirable organisms, increases favorable chemical action, 
and makes the soil a much more desirable home for 
plants. It warms the soil earlier in the spring, thereby 
increasing the length of the growing season of crops. 
Drainage improves the sanitary conditions of a region 
by drying the breeding places of disease germs and dis- 
ease-carrying insects. It lessens the winter-killing of 
crops by reducing heaving of the soil, and it decidedly 
improves structure and tilth. All of these benefits work- 
ing together result in a good net profit in almost every 
case in which drainage is properly done. It isa common 
L 
