50 DRAINAGE 



render the soil porous, though maintaining a sufficiency of moisture 

 for plant-life ; to remove superfluous water and prevent stagnant 

 water remaining in the soil. A porous soil contains small spaces 

 between its particles, and these, when not occupied by water, are 

 rillecl with air, which conduces to bacterial activity and nitrification 

 and is essential to plant-growth. Some lands are naturally well- 

 drained, which may be seen from the fact that when rain falls on 

 them it percolates through without leaving the soil sodden or 

 saturated. Soils which are not properly drained become impreg- 

 nated with acids which are injurious to plant-life ; in such cases 

 the soil is cold, and causes the roots to rot off from the ends, the 

 plants under such conditions being sometimes referred to as 

 suffering from "wet feet." A damp soil is always colder than a 

 porous one, for the reason that water is colder than air. 



Surface drainage, i.e., open trenches or ditches at certain 

 intervals, are essential on steep lands, so as to prevent or check the 

 washing away of the surface soil by torrential rains. This system 

 of drainage is extensively employed throughout the Tea-planting 

 districts, and is indispensable to the preservation of the soil. The 

 drains are usually about 2 to 3 ft. in depth, and vary in the distance 

 apart according to the gradient and physical characteristics of the 

 land. On very steep land such drains should not be more than 

 25 to 30 ft. apart, while on gentle slopes they may be as many yards 

 distant. 



In gardens or ornamental grounds, however, open drains 

 would be unsightly if not impracticable, and for that reason they 

 should be covered, notwithstanding the extra cost thus incurred. 

 In making a covered drain, drainage tiles or stones should be 

 placed in the bottom of the trench, large spaces and crevices being 

 left in the bottom, and Finishing with a layer of smaller pieces at 

 the top. Brushwood, fibre, or straw may be placed over this, and 

 the soil then filled in. (See Drains and Culverts}. 



