The cropping season is lengthened by causing the soil to be warmer and drier earlier in the spring and later in the fall.
Influence on plant food in the soil.
Covered or under drains check losses of plant food that occur with surface and open ditch drains. They render available more plant food, for lowering free water and increasing ventilation:
Deepen the feeding area of the roots.
Aid the process of nitrification.
Aid chemical changes which make plant food available.
Check denitrification.
LOCATION OF DRAINS
As gravity is the force that is to take the surplus water from the soil, the outlet of the drainage system should be at the lowest part of the area to be drained.