SOIL RECLAMATION AND IMPROVEMENT 95 



this purpose the most suitable source in dry climates is a 

 river which can be relied upon to run in dry weather. Such 

 are, however, scarce, and are chiefly to be found in rivers 

 that travel from long distances, or originate in snow moun* 

 tains. The rivers originating in the Himalayas are specially 

 suitable for this purpose, since the melting of the snows in 

 the summer gives ample supplies of water. The Nile, rising 

 a great distance away, gives a flow of water at the right time. 

 The erection of dams or barrages across the river will hold 

 the water up, and divert it into proper channels, which then 

 communicate with distributing channels of smaller size. 

 The supply of water by these means depends upon the 

 organization of distribution. In Madras, and many parts 

 of India, very old-established tanks occur, which have been 

 originally produced by the utilization of some natural 

 depression by building a dam across the original outlet. The 

 rainfall is collected from a small area, but the natives collect 

 considerable quantities of water in the rainy season, and 

 utilize it in the dry season. When the water from such 

 tanks has been let out, the wet, muddy bottom is used for 

 cultivation of rice. From such large, open tanks the loss 

 of water by evaporation is very considerable. The expense 

 of instituting such a system would be very heavy, but nearly 

 all these somewhat primitive arrangements have been 

 produced by degrees, mostly utiHzing labour which would 

 otherwise have been wasted. The water is applied to such 

 dry lands by running the water along channels, the distance 

 between which will depend upon the type of crop grown. 

 There is a great tendency on the part of the users to take 

 more than is necessary. Deep ploughing only lets the 

 water of the subsoil evaporate. Mulches should be used as 

 much as possible. Many soluble manures, especially phos- 

 phates, economize water. Nitrogenous manures, such as 

 sulphate of ammonia, if applied when the plant is suffering 

 from drought, may often increase the crop. 



Wet Lands.— Wet lands require, as a rule, drainage. 

 Drains should be set not too deep, and should lead without 

 any very sharp angles into the main drain. By such a 



