Methods of irrigation

Irrigation supplies water to crops when rain is not enough or not timely. The method chosen decides how much of the water drawn from a canal or well actually reaches the crop roots, and so how far a scarce resource stretches. Methods are grouped as surface, sprinkler and drip (micro) irrigation.

Surface methods spread water over the field by gravity. Flooding of basins suits paddy and level land. Border strip irrigation runs water down long, gently sloping strips between low ridges, suiting close-growing crops like wheat. Furrow irrigation runs water along small channels between rows, suiting cotton, sugarcane and vegetables. Surface methods are cheap and need no energy beyond lifting water, but efficiency is often low because of deep percolation and runoff at the field end, and they need well-levelled land; laser land levelling helps a great deal.

Sprinkler irrigation sprays water through nozzles under pressure, imitating rain. It suits undulating land, sandy soils and many field crops, with efficiencies around 70 to 80 percent, but wind and evaporation cause losses, and it needs pumps and pipes. Drip irrigation delivers water slowly to each plant's root zone through emitters on lateral pipes, with efficiencies often above 90 percent. It also allows fertigation and suits orchards, vegetables and sugarcane, though filters and maintenance are essential to stop clogging. Subsurface irrigation, by controlling the water table, is used locally. Choice depends on crop, soil, slope, water availability and cost.