Most arable land have some kind of a drainage
system. An exception is steeper hillsides where the water drains
out on top of the soil anyway.
Drainage allows to to grow plants in areas that otherwise would be marshland or wetland. Drainage also increases crop yield.
Drainage system provides good growing conditions for the plants that in turn is the best guarantee for minimizing nitrogen leaching.
The draining system forms the base for CDI. It is required for the Controlled Drainage that in turn is required for the sub-irrigation.