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Wheat would give off about 260 tons per acre, Other crops would 

 give off corresponding amounts. It appears that cruciferous crops 

 like mustard and rape probably give off more than any other class 

 of plant. But nevertheless the amount of evaporation from the 

 leaves of a tea bush must be very great, and probably accounts for the 

 ttosorption of water corresponding to a good many inches of rainfall 

 during the season. 



It might be thought, however, that such questions were entirely 

 unpractical and beside the point in the tea districts, where the 

 necessary rainfall is so extremely high as to make it appear that, primd 

 facie^ a tea planter should be independent of these considerations. 

 Doubtless such is the case in most of the Upper Assam districts. 

 Away from these districts, however, the conditions are quite different, 

 for here, although the rainfall is very great, yet it is so unevenly distri- 

 buted, that while at one time the great question may be removal of 

 water with the greatest speed possible, yet at another, really only a 

 few weeks later, the cry goes out that the tea plants are dying for 

 want of moisture. We have, in fact, a combination of a rainy and an 

 arid district, of a high rainfall and a scanty water-supply, of rain in 

 more than sufficient amount at one season of the year, and of long 

 droughts, often lasting six months, with hardly any appreciable 

 rain, for the remainder, It is necessary to consider therefore both 

 the means of removal of excess of water in the rains and the 

 conservation of the precious soil water supply in the dry weather. 



REMOVAL OF WATER BY SUBSOIL DRAINS. 



The removal of the excess of soil water, and especially of 

 subsoil water, is the most important and primary function of sub- 

 soil drains, whatever other purpose they may incidentally serve. 

 It is not often enough recognised that the proper object of drainage 

 of the kind used in tea gardens is not so much to take the water 

 falling on the surface as to prevent a rise in the level of the 

 ground water, and that hence the water ought to rise into the drains 

 from below to a greater extent than it soaks in from above. Be 

 this as it may, and the point is not one of great importance, it is now 

 generally appreciated that the presence of ground water at a 

 certain depth is an indication that such depth is the absolute limit 

 of the depth of tea root development. Of course those soils in 

 which the water level is so far below the surface as to cause no 



