Groundwater is generally a more dependable source of irrigation than surface water and is free from seeds and plant organisms. The first cost of installation is however, high. The best water bearing stratum or aquifer is coarse gravel free from sand but such formation are rare to find. An aquifer is a saturated formation which creates ground water reservoir and yields sufficient quantity of water to wells or springs. These are made of unconsolidated formations like sand, gravel, fractured rocks.
Sub â€'surface Irrigation:
It is termed as sub â€'surface irrigation, because in this type of irrigation, water does not we the soil surface. The underground water nourishes the plant roots by capillarity. It may be divided into the following two types:
1. Natural sub â€'irrigation; and
2. Artificial sub â€'irrigation.
Natural sub â€'irrigation: leakage water from channels, etc., goes underground, and during passage through the sub â€'soil, it may irrigate crops, sown on lower lands, by capillarity. Sometimes, leakage causes the water â€'table to rise up, which helps in irrigation of crops by capillarity. When underground irrigation is achieved, simply by natural processes, without any additional extra efforts, it is called natural sub â€'irrigation.
Artificial sub â€'irrigation: when a system of open jointed drains is artificially laid below the soil, so as to supply water to the crops by capillarity, then it is known as artificial sub â€'irrigation. It is a very costly process and hence, adopted in India on a very small scale. It may be recommended only in some special cases with favourable soil conditions and for cash crops of very high return. Sometimes, irrigation water may be intentionally collected in some ditches near the fields, the percolation water may then come up to the roots through capillarity.