Practical means of scheduling irrigation of maize using a programmable pocket calculator

Abstract

The irrigation scheduling model IRRISCHED-4, here described, enables the irrigator to choose one of four techniques for estimating crop water use, depending upon data available. Daily inputs include maximum and minimum temperatures, sunshine hours, leaf area index, crop factor, rain, and irrigation. The model is run on a programmable pocket calculator. The techniques used in determining daily soil-water status depend on Class A pan evaporation, the Linacre and Blaney & Criddle equations, and a modified version of the Priestley & Taylor equation. These four techniques were tested over two seasons at Cedara and compared to lysimeter-determined values of evapotranspiration. All methods perform satisfactorily but the modified Priestley & Taylor method provided the most reliable evapotranspiration estimates, owing to the utilization of leaf area index data.