Why irrigation

Irrigation supplies water to crops when rainfall is not enough or does not come at the right time. In India, with most rain falling in a few monsoon months and a long dry season, irrigation is what makes a second or third crop possible and protects farmers from failed rains.

Water comes from surface sources, rivers stored behind dams and diverted by barrages into canals, or from groundwater pumped from wells and tube wells. It reaches the field by flooding, furrows or basins, or by more efficient sprinkler and drip systems that put water near the roots and waste less.

Planning starts with crop water need: how much water a crop uses over its season, plus losses in conveyance and application. Duty and delta are traditional Indian terms that link a discharge to the area it can irrigate and the depth of water a crop needs.

Poorly managed irrigation brings problems: waterlogging and salinity when drainage is neglected, and falling water tables where groundwater is over-pumped. Good design includes drainage and measures water.