EVALUATION OF IRRIGATION SCHEDULING PROGRAM AND SPRING WHEAT YIELD RESPONSE IN SOUTHWESTERN COLORADO

Effective irrigation scheduling to manage water fur spring wheat (Trit icum aestivum L.) in southwestern Colorado was investigated under vari able water applications. This study was conducted (1) to determine the effects of varying rates of water replacement (GET, 0.33ET, 0.67ET, 1 .0ET, and 1.33ET) on spring wheat grain yield, dry matter yield, root water uptake, and water use efficiency, (2) to develop local crop coef ficients, and (3) to I:valuate the irrigation scheduling program calle d 'SCHED' that had been used in the area, Daily weather data was used to calculate reference ET using the Penman equation. Crop ET was predi cted by using the irrigation scheduling program, 'SCHED'. Both grain y ield and dry matter increased significantly with the increase in water application rates, up to 1.0ET application rate. Crop coefficients es timated at various water application rates were greater than the value s used in the irrigation scheduling program. Total water use efficienc y (TWUE) and irrigation water use efficiency (IWUE) for grain yield we re considerably greater at 0.33ET than for other rates, whereas TWUE a nd IWUE for dry matter yield followed the order 0.33ET > 1.0ET > 0.67E T > 1.33ET > GET. (C) 1997 Elsevier Science B.V.