68 



TROPICAL AGRICULTURE 



CHAP. 



Drainage 



causes 



fertility. 



Drainage 

 pipes and 

 tiles. 



Outlet of 

 drain to be 

 kept clear. 



Soil must 

 not be over- 

 drained. 



from the soil, and thus to make it warmer, to restore its 

 porosity, to make it sweeter by the removal or alteration of 

 the vegetable acids, and, in short, to make it more fertile. 



Most of the land in the West Indian Islands being of a 

 hilly nature, it may be easily drained by digging deep, open 

 trenches so as to carry off the surplus water to the lowest 

 part of the estate, or to a stream in the vicinity. The 

 depth of the main trench or ditch will depend on the 

 nature of the soil, the amount of water and the lay of 

 the land, but it should not be less than three or four 

 feet, as the roots of many cultivated plants go deep into 

 the soil, and it does them much harm to be kept in standing 

 water. 



A more expensive way is to make covered drains, which is 

 done in the following manner : — The trench should be dug 

 wide at the top ; and at the bottom, which should be smooth 

 and sloped gradually, it must not be wider than it can be 

 made without the sides falling in. Along the bottom are 

 placed drainage pipes or tiles. The latter are simply flat 

 earthenware tiles curved in a semi-circular manner, and 

 they form an arch to allow the water to run freely under- 

 neath and to support the earth with which the trench is 

 filled up. Small stones and pebbles should first be placed 

 over the tiles ; or, if they cannot be got, brushwood or 

 straw or cane trash may be used ; surface earth, but not the 

 clay from the trench, is then filled in over this, and the 

 drain is complete. The outlet must be kept clear, and 

 provided this be done there is very little chance of the 

 drain becoming choked. Another way is to fill the trench 

 nearly to the surface with stones, large ones being placed 

 at the bottom and smaller ones on top. 



Of course in draining land, as in all other agricultural 

 operations, experiments will often teach useful lessons. By 

 deepening drains, or by running cross drains into them, the 

 fertility of the land may be much increased, but care must be 

 taken not to overdrain a soil. The object of drainage is not 



