108 THE PRINCIPLES OF AGRICULTURE. 



Draining. The draining of land, for the purpose of re- 

 moving surplus water in wet seasons or in wet places, is 

 accomplished either by surface drains or by underdrains. 



Surface drains, or ditches, are of some advantage in 

 removing the surplus accumulation of water from the 

 surface of the ground. Besides being unsightly and in- 

 convenient, they have the disadvantage of causing some of 

 the richer portions of the surface soil to be washed away. 



Underdrains are buried out of sight, involve no waste, 

 and accomplish the purpose more effectually. The gen- 

 eral advantages to be gained by underdraining wet land 

 are as follows : 



1. It renders the lower soil available to roots. 



As the roots of most agricultural plants cannot live 

 without the presence of oxygen, they cannot occupy 

 soil which is completely saturated with water. Where 

 the lower portions of soil are filled with water, roots 

 are necessarily confined to the surface soil. By drain- 

 ing, we afford them an opportunity to make their way 

 downward. 



2. It admits air to the lower soil. 



From soil whose pores are filled with water, air is, of 

 course, excluded. In such soil the formation of plant 

 food mostly ceases. In a muck bog the humus retains 

 its elements in an insoluble condition for centuries. 



By draining the water out of soil, we admit air, and 

 provide for the formation of plant food. 



3. It secures the benefits of rain. 



Rain water, containing nitric acid, ammonia, etc., is a 

 source of fertility. In falling upon soil that is already 

 filled with water, it cannot penetrate into the soil, but 

 runs away upon the surface. Thus, the benefits of the 

 rain are lost. Where water is withdrawn from the soil 



