Sub surface drip irrigation (SDI) is a type of micro irrigation system using drip tube or tape, installed below the root zone (see picture). It is the slow, frequent application of water to the soil profile directly to the root zone of plants, beneath the soil surface. Allows the precise application of water, nutrients and other chemicals.

Properly managed SDI systems wet the root zone uniformly through the field while maintaining a dry soil surface.

Crop selection, soil type and cultural practices determine system capacity, emitter spacing and lateral depth and spacing. For most row crops, emitters should provide overlapping wetted areas along the lateral. Lateral spacing  should be narrow enough to provide a uniform supply of water to all plants (see pictures).

Chemicals and fertilizers can be added during irrigation but the selection of products -to suit nutrient requirements- should include factors such as solubility, compatibility and reaction of salts in the irrigation water.