Effect of Weather Variability and Precipitation Uncertainty on Grain Sorghum Irrigation Scheduling

Abstract

ABSTRACT Asimulation study was conducted to characterize the impact of year-to-year weather variability on irrigation scheduling of grain sorghum {Sorghum bicolor (L.) Moench) and to quantify the effect of precipitation forecast uncertainty on irrigation schedules evaluated weekly. The simulations were performed for a period of 30 years (1950-79) for locations with a semi-arid (Lubbock, TX) and a subhumid (Temple, TX) climate. Full and partial profile rewetting irrigation strategies and low and high water holding capacity (WHC) soils were considered. Precipitation amounts for the 30% (wet week) and 70% (dry week) probabilities of exceedence for each week of the growing season were used as precipitation forecast. The year-to-year weather variability, particularly precipitation, was found to limit the use of fixed irrigation schedules at both locations. In these variable environments, the impact on yield and net irrigation amounts of assuming a dry or a wet week for irrigation scheduling was low for all combinations of soil WHC and irrigation strategy, indicating that precipitation forecast may not be a significant factor for irrigation scheduling decisions evaluated with short intervals.