90 ELEMENTS OF AGRICULTURE 



92. Seepage from Canals. Over half the water turned 

 into canals in the United States is lost before it reaches 

 the fields. In India, 47 per cent is lost from many canals. 1 

 Some of this loss is due to evaporation, but most of it is 

 due to seepage. If the water carries considerable silt, 

 the losses are less. Silt is one of the greatest factors in 

 making canals water-tight. Care in canal construction 

 will also save considerable water. 



Seepage not only causes a loss of water, but it often 

 injures large areas of land, because of the deposits of 

 alkali by the water, or because of the rise of alkali with 

 the evaporation of the water. 



93. Over-Irrigation. This not only wastes water, but 

 the excessive amounts are a detriment to crops. It also 

 aids in spoiling the land by making the accumulation of 

 alkali more rapid. It is more profitable to use moderate 

 amounts of water and follow by tillage to prevent evap- 

 oration. 



94. Alkali. In arid regions, very little of the water 

 drains away as it does in humid regions. Nearly all the 

 water evaporates from the soil. The water contains 

 small amounts of salts in solution and these are left by 

 evaporation. The process is similar to the formation of 

 salt lakes. The best remedy is drainage. By under-draining 

 the land and flooding it, the salts may be carried away 

 with the water. Some soils have such good natural under- 

 drainage that artificial drainage is not necessary. If the 

 land is flooded without drainage, the water sinks into the 

 soil, and, as it rises, brings with it more alkali to be left 

 near the surface. 



l Cyclopedia of American Agriculture, Vol. I, p. 422. 



