TN-11 : Water requirement of crops

Abstract

It has become essential to make effective use of the available water resources allocated for agricultural purposes. Besides better methods of land preparation, proper management of irrigation water and improved cultural practices, it is necessary to improve the estimates of crop water requirements based on climatic data. Procedures for estimating crop water requirements should provide consistent and reliable results, and require minimum of data and computation. A reliable estimation of crop water requirements will help planning, design and execution of an irrigation project.

The present technical note describes various methods of estimating crop water requirements. A review of various empirical relations for determining evapotranspiration has been presented. Application of various empirical relations has also been discussed giving details of data requirement. The various instruments required to collect the necessary data have also been mentioned. The F.A.O., in its Irrigation and Drainage paper No.24, described four methods viz., Blaney Criddie, Radiation, Modified Penman, and Pan evaporation far estimating reference evapotranspiration and listed a computer program Laing these methods for computing evapotranspiration. The program has been unpilemerited on VAX-11/780 computer system of the institute and the resits far a set of data are given. An exhaustive bibliography is given at the end of the note.