36 THE SOIL OF THE FARM. 



yerse of land drainage, is but another example of tlie 

 fertilizing use of water when properly employed. In 

 both cases it is the passage of water through the soil 

 which is the object aimed at ; in both the water is useful 

 as a carrier of temperature and of various elements of 

 plant food ; in both the benefit is derived to some extent 

 from the increased activity induced in those chemical 

 processes within the soil by which i3lant food is derived 

 from the comparatively inert condition in which it nat- 

 urally lies. In both processes it is the stagnation of 

 water upon or in the soil which is the evil to be removed; 

 and there is rarely any good derived from irrigation un- 

 less it be accompanied by land drainage. Of course the 

 conditions under which the process is conducted are very 

 different in different climates, and in our temperate 

 climate we can hardly realize the advantage of irrigation. 

 In many tropical countries rain falls so seldom, and at 

 such lengthened intervals, that field irrigation affords 

 the only possible chance for the former to grow profitable 

 crops. In our own country it is not as the necessary pro- 

 vision in the absence of w^hicli the land would be barren, 

 but it is only as increasing the activity of the fertilizing 

 agencies already present that irrigation acts. 



Soils suited to Irrig^ation, — Light porous soils, and 

 particularly gravels and sands, are most improved by 

 irrigation. Tenaceous and clay soils are seldom benefited 

 by it ; never, except in connection with thorough draining. 

 In all cases, indeed, the drainage of the land must pre- 

 cede its irrigation. The soil to be irrigated must be 

 in a condition enabling it to drain itself dry ; otherwise 

 irrigation, so far from proving a benefit, may be produc- 

 tive of the worst results. It is not only important that 

 water be brought into the ground ; it is equally imjiortant 

 that it should ]\ass off immediately after accomplishing 

 the object sought. 



