3. Efficiency

Irrigation efficiency is defined as the ratio between the water stored in the soil depth inhabited

with active plant roots to the water applied by the irrigation system. Thus, water applied by the

irrigation system and not being made available to be taken up by plant roots is wasted and reduces irrigation efficiency. The major causes for reduced irrigation efficiency are drainage of excess irrigation water to soil layers deeper than the depth of active roots. Leakage of irrigation water to deep soil layers could result in pollution of the water table. Over-irrigation and under- irrigation, both are injurious to the crop. Thus, the timings of irrigation and the quantity of water supplied are decisive for the satisfactory performance of the crop. In the case of wheat for example, appropriate timing and spacing of irrigation raise the yield as much as 50 per cent with less use of water.

The cases of irrigation efficiency of 100 percent are practically none existent even in the most modern irrigation systems. Major difficulties in obtaining high irrigation efficiency stems from the inability to obtain an accurate estimate of the quantity of water needed to recharge the soil root zone depth and the lack of valid, real time information concerning the actual soil depth of active roots.

Conservative estimates suggest that even under optimal management practices the average

irrigation efficiency is estimated to be 70 percent. Thus, the average water loss under sprinkler and drip irrigation is 30 percent but could drop to values of over 50 percent under furrow and flood irrigation. Efficiency of drip irrigation can reached to 90 per cent with best efforts. Water losses of irrigation water under urban and landscape irrigation could easily reach 50 percent of the applied water.

India’s national water mission aims to increase water use efficiency by 20 per cent. Agriculture contributes for more than 80 per cent of water usage in the country. Therefore, a large focus of the mission is on the improving efficiency of various irrigation projects such as Major & minor irrigation schemes, CAP&WM (Command Area programmme & Water Management), and AIBP (Accelerated Irrigation Benefits Programme) etc.