CHAPTER XIV. 

 PRINCIPLES OF FARM DRAINAGE. 



Both irrigation and drainage are usually looked upon as 

 arts whose application to agriculture are required only in 

 special cases; but a broader and more helpful conception is 

 that all fertile fields must be both well irrigated and thor- 

 oughly drained. 



It is true that over much the larger portion of the earth's 

 surface the water required for the growth of crops is sup- 

 plied by the natural rainfall, and when this is timely and 

 sufficient it is the best and ideal irrigation, done by nature's 

 hand. 



It is again fortunately true that most land areas have ac- 

 quired such surface features that the excess of rainfall is 

 opportunely removed by percolation and seepage or surface 

 flow; and this is nature's method of land drainage. 



The fundamental fact is that all lands must be irrigated 

 or watered and drained and in special cases nature's efforts 

 need to be supplemented. 



355. Necessity for Drainage. There are several impera- 

 tive demands for the drainage of farm lands: 



1. The removal of the more soluble salts formed by the 

 decay of rock and organic matters, because when the soil 

 water becomes too strong in soluble salts it either poisons 

 the plant or renders the root hairs inactive by causing them 

 to shrivel. If these soluble salts which plants cannot use 

 are not removed the soil comes into the condition known 

 as alkali lands, upon which little vegetation can grow. 



2. The water in the soil needs to be frequently changed 

 or replaced by a fresh supply containing an abundance of 



