The objective of subsurface drainage is to drain excess water and salt from the plant root zone of the soil profile by artificially lowering the level of water table (Figure 6) Subsurface drainage improvement is designed to control the water table level through a series of drainage pipes (or tubing) that are installed below the soil surface (Figure 7). The subsurface drainage network generally outlets to an open ditch or stream. Subsurface drainage improvement requires some minor maintenance of the outlets and outlet ditches. For the same amount of treated acreage, subsurface drainage improvements generally are more expensive to construct than surface drainage improvements. The main objective of drainage is to remove excess water quickly and safely to reduce the potential for crop damage.
Types of subsurface drainage systems
Subsurface drainage aims at controlling the water table and a control that may be achieved by tubewell drainage, open drains or subsurface draims (pipe drains or mole drains). Tubewell drainage and mole drainage are applied only in very specific in conditions. Subsurface (groundwater) drainage for water table and soil salinity in agricultural land can be done by horizontal and vertical drainage systems. Horizontal drainage systems use open ditches (trenches) or buried pipe drains.
Figure 6 : Level of water table before and lowered level after drainage improvement: (a) surface drainage ditch; (b)subsurface drainage pipe.
Figure 7: A controlled level of water table profile under subsurface drainage
Draining excess water from the soil profile where plant roots grow help aerates the soil and reduces the potential for damage to the roots of growing crops. It produce soil conditions more favorable for farming operations.