Title

Abstract

Improved irrigation water management requires accurate scheduling of irrigations which in turn requires an accurate calculation of daily crop evapotranspiration (Et). Previous work by Neale et al. (1989) and Bausch (1993) have indicated that the reflectance-based crop coefficient (Kcr) for corn responded to crop growth anomalies and should improve irrigation scheduling. Thus, the purpose of this study was to develop a new procedure for using the Kcr in irrigation scheduling and present results of simulations comparing different basal crop coefficient (Kcb) curves for corn to evaluate their effects on estimated crop Et. Irrigation scheduling simulations were performed using SCHED, the USDA-ARS Irrigation Scheduling Program, and three Kcb curves (the one in SCHED, Wright's (1982) tabular data, and the Kcr-based Kcb). Simulated crop water use using the Kcb curve in SCHED was considerably greater during vegetative growth (60 to 100 mm) than simulated crop water use using Wright's Kcb or the Kcr derived Kcb curves for three growing seasons. Crop water use between the Kcr-basedKcb and Wright's Kcb were different by approximately 20 mm each growing season. Crop water use was less in 1990 and 1992 for the Kcr derived curve and greater for 1991; crop development was directly responsible for the differences. Although the differences between the Wright and Kcr basal crop curves were minimal, irrigations with the Kcr-based Kcb were more appropriately timed. Irrigations that are correctly timed minimize overirrigation as well as underirrigation.