Irrigation water is an expansive input and has to be used very efficiently. The main losses that occur during irrigation of fields as conveyance, run off, seepage and deep percolation. Irrigation efficiency can be increased by reducing these losses. Uneven spreading and inadequate filling of root zone are the other causes for low irrigation efficiency. Irrigation efficiency at the field level can be increased by selecting suitable method of irrigation, adequate land preparation and engaging an efficient irrigator. At the project level, it can be increased by proper conveyance and distribution system. Irrigation efficiency is the ratio usually expressed as percent of the volume of irrigation water transpired by plants, plus that evaporate from the soil, plus that necessary to regulate the salt concentration in the soil solution and that used by plants in building plant tissue to total volume of water diverted, stored or pumped for irrigation.
Wt + Ws – Rs
Ei = ——————– X 100
Ei = Irrigation efficiency (percent)
Wt = the volume of irrigation water / unit area of land transpired by plants, evaporation from the soil during the crop period.
Ws = the volume of irrigation water per unit area of land to regulate the salt Content of soil solution.
Re = Effective rainfall
Wi = the volume of water per unit area of land that is stored in reservoirs or diverted for irrigation. Irrigation efficiency indicates how efficiency the available water supply is being used. The efficiency of irrigation projects in India is as low as 20 to 40%.