ABSTRACT
Based on the source of water for crop water use, agricultural production systems are broadly classified as rainfed agriculture systems wherein the entire crop water use is met from rainfall and irrigated agriculture systems wherein the available rainfall is supplemented with external water supplies. It is estimated that at present 277 million hectares i.e., about 18% of world’s arable land is under irrigation and is responsible for about 40% of the crop output (International Commission on Irrigation and Drainage – ICID, 2006). Even though at present contribution of rainfed agriculture to the world’s food production is more than the irrigated agriculture, there is a considerable effort to shift to irrigated agriculture where ever possible. This is for the reason that the relative immunity which irrigation offers from an erratic or inadequate rainfall. With assured water supply from irrigation farmers are able to invest in other inputs like fertilizers, improved tillage practices etc., in order to obtain higher crop yields. Figure 8.1 shows in general the yield potentials of rainfed and irrigated agricultural systems.
