SIGNIFICANCE OF ESTIMATING CROP WATER REQUIREMENTS (CWR)

Crop water requirements are useful in determining when to irrigate and how much water to apply. Evapotranspiration information is needed in determining the volume of water required to satisfy short term and seasonal water requirements for fields, farms and irrigation projects (Burman et al., 1980). Irrigation water requirement is one of the principal parameters for planning, design and operation of irrigation and water resources systems. The incorrect estimation of the irrigation water requirement may lead to serious failures in the system performance and to waste of valuable and scarce water resources. For planning and design purposes, irrigation water requirement has to be studied with respect to the magnitude and variability of the seasonal and peak period irrigation water requirements (Svehlik, 1987). Actual measurements of consumptive use under physical and climatic conditions of any large area are time consuming and expensive. Thus, reliable methods are needed to determine consumptive use. Numerous equations that require meteorological data have been proposed and several are commonly used to estimate ET. The calculation of ET estimates from weather records is appealing because the approach is relatively simple. The calculated reference crop ET can be used to estimate actual ET by using coefficients to account for the effect of soil moisture status, stage of growth and maturity of a crop (Burman et al., 1980). During the planning and design stages it is important to accurately determine the crop water requirements for any irrigation set-up in order to establish whether the source of water can satisfy demand. This is particularly important at peak demand. The crop water requirement figures can used to establish the area that can be irrigated from a given amount of water following a given cropping program. Again costs of delivering water from source to the field can be estimated using crop water requirement figures. [J.M. Makadho and F.Butling, 1987]