ESTIMATING EVAPOTRANSPIRATION FROM IRRIGATED CROPS IN SOUTHWESTERN ONTARIO

Abstract

Several years of daily evapotranspiration (ET) data for irrigated early potatoes, corn and processing tomatoes, grown on Fox sandy loam measured by floating lysimeters and estimated by meteorological data were used to evaluate an equilibrium evapotranspiration (ETeq) model. A reasonable relationship was obtained between values estimated by the model and those measured by floating lysimeters. The ETeq model can be used to estimate daily ET over a wide range of soil moisture and foliage cover conditions. ETeq can be estimated from readily available climatic data in the form: ETeq = (0.48 + 0.01 Ta) [(0.114 + 0.365n/N) K↓a − 0.039]; where Ta is the mean daily air temperature (°C); n is sunshine duration (h); N is maximum hours of bright sunshine (h); K↓a is solar energy received at the top of the atmosphere (mm/day). At high soil water storage in the root zone, the ET/ETeq remained constant, whereas, at low soil water storage, the ET/ETeq decreased linearly with decreasing soil water storage. The total crop yields were directly related to growing season accumulated ET.