Irrigation and Drainage 145 



plants is prevented. Drainage, which gradually removes 

 these salts, is the only method of reclaiming 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. 



Effects of drainage. 



The drainage of wet land im- 

 proves it in many indirect, as well FIG. 22. Drainage 

 as direct, ways. Lowering the trench dug with a machine. 



/ It is ready for the tile. 



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 aeration 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 is a common 

 L 



