SOIIy DEFICIENCIES 269 



more frequent or the land must be under-drained. Too frequent 

 flooding may keep the ground too wet, so that under-drainage is 

 really the practical remedy. Whenever the water-table is at such 

 a distance that the capillary action of the soil can bring water 

 from it to the surface, there is great danger of alkali. In such a 

 soil, the rise of water from the ground water is continuous, so 

 that more must be used in irrigation to cause the main movement 

 of the water to be downwards. By lowering the water-table by 

 means of drainage, the water-table may be brought below the 

 power of the soil to elevate it, thus checking the movement of 

 water, and the alkali with it, towards the surface. The right 

 depth for the water table depends upon the character of the soil. 

 In coarse sand, water may be raised over five feet. It appears 

 possible that in fine sand, so often found in alkali districts, water 

 may be raised as much as twelve to fifteen feet. 



How much flooding will keep the main movement of the water 

 downward and through the soil will depend, therefore, upon the 

 water-table and the character of the soil, and the thoroughness of 

 the cultivation. The composition of the ground-water, and the 

 composition of the irrigation-water are important factors to 

 consider. 



The alkali question is, in many localities, largely a question of 

 proper drainage. 



Quantity of Irrigation Water. The quality of the irrigation 

 water which can be used upon soils without injury depends upon 

 the kind of soil, the character of the under-drainage, the rainfall 

 of the area, and the manner in which the water is used. If the 

 soil is easily penetrated by water, and well drained, water of 

 comparatively high mineral content may be used, provided that 

 it is used in such a manner as to keep the main movement of the 

 water through the soil and into the drainage. In humid regions, 

 a water containing more salts may be used than in arid regions, 

 since less water is used and the natural rainfall will aid in wash- 

 ing the alkali out of the soils. With a heavy clay soil, however, 

 and especially if alkali carbonates are contained in the water, 

 there is always danger. 



