In areas where the topsoil is of high quality and porous and there is an underlay of clay soil that absorbs water slowly, conditions exist for natural sub-irrigation, provided that the water table is high. Ditches dug along the fields can be used to monitor the water level and to also replenish the water supply when it is low. Where there is little or no rainfall and the salts in the water build up on the surface of the soil, leaching is carried out. To overcome excess rain in areas where sub-irrigation systems are in use, water can be removed by pumping or using natural gravity features available in the terrain, that is, slopes and depressions in the ground.
When sub-irrigation is desired but the conditions are not available naturally, pipes with evenly distributed punctures can be buried underground. A difficulty involved with these systems is that they can be damaged when the soil is being cultivated. These systems also work by the use of natural sloping features in the terrain or by pumping water through the pipes.
Drip irrigation, which is not actually sub-irrigation, but uses some of the same principles as in sub-irrigation, delivers water slowly to the root areas of plants. Here, too, pipes are used as the channels for transporting the water and emitters are placed to water plants directly. While it is economical to use because there is little waste of water and evaporation is at a minimum, initial costs of installing drip irrigation systems are higher than other methods. There is also a tendency for emitters to become clogged by the salts in the water. Salts, however, do not build up around the roots of plants in drip irrigation systems.