Abstract
Evapotranspiration is one of the most important factors for irrigation management. This study was conducted to develop and test a new method to determine evapotranspiration. Measurements of evapotranspiration, transpiration, soil evaporation, soil water status, sunlit leaf temperature, air temperature, imitation leaf temperature, plant coverage, leaf area index, and micro-meteorological parameters were made in a one hectare grain sorghum (Sorghum bicolor (L.) Moench.) field to verify the proposed method. A new equation was developed to estimate canopy evapotranspiration by introducing the temperature of an imitation leaf. The required parameters of this method were sunlit leaf temperature, imitation leaf temperature, air temperature, plant coverage, and solar radiation. The major advantage of the proposed method was that the plant correction factors, canopy resistance, and aerodynamic resistance were not required. By neglecting the evaporation from the soil surface where it is shadowed by a canopy (canopy shadowed soil), the suggested method was quite accurate to estimate plant transpiration. Field experimental results showed that the calculated daily and longer-period transpiration by the proposed method were consistent with the estimated results by lysimeters. The regression coefficients between daily estimated and calculated transpiration was r=0.94. In addition, the short period transpiration measured by porometer agreed well with the calculated transpiration by the proposed method. Therefore, it can be concluded that the suggested approach is a simple and accurate way to estimate plant transpiration.
