Water Requirement and irrigation Efficiency
For on farm irrigation management with reference to crop planning, the estimation of water requirement of crops is of prime importance. The crop water requirement is defined as the quantity of water, regardless of its source, required by a crop or diversified pattern of crops in a given period of time for its normal growth under field conditions at a place. This includes the losses due to evapo-transpiration or consumptive use plus the losses during the application of irrigation water (unavoidable losses) and the quantity of water required for special operations such as land preparation, transplanting, leaching etc. The irrigation demand, however, refers to the crop water requirement, exclusive of effective rainfall and contribution from soil profile. The irrigation requirement of an outlet command area includes the irrigation requirement of individual farm holdings and the losses in the conveyance and distribution system.
The design of the irrigation system, the degree of land preparation and the skill of the irrigation are the principal factors influencing effectiveness of irrigation. The irrigation efficiency indicates how efficiently the available water supply is being used based on different methods of evaluation. The ratio of crop yield to the amount of water depleted by the crop in the process of evapo-transpiration is termed as crop water use efficiency. On the other hand, the ratio of crop yield to the total amount of water used in the field is termed as field water use efficiency. Of the two indices, the concept of crop water use efficiency is of fundamental interest while field water use efficiency in of greater practical importance.