Transpirations Efficiency of Oat

Dry matter production, water use, and their ratio (ie., the water use efficiency [WUE] of crops) vary among species and with climatic conditions. This study was undertaken to determine the WUE of oat (Avena sativa L.) because recent field evaluations for this crop are not available. Oat was grown on loess‐derived silt loam (finesilty, mixed, mesic Typic Hapludalf) near Goettingen, West Germany, during 4 yr. Periodically, shoot and root dry matter were determined. Water use within five consecutive growth stages was evaluated by the soil water budget approach. Balanced evapotranspiration (ET), including evaporation from soil (E), water intercepted by leaves (I), and transpiration from plants (T), was divided into its components, E, I, and T by calculation procedures. The term E was approximated from meteorological factors, leaf area index (LAI), and soil water tension, and I from daily precipitation and LAI. Shoot and total oat dry matter including roots were linearly related to cumulative T, IT, and ET. The x‐intercept of the regression line was nearest to zero, when ✕ was IT. Therefore, I was regarded to be part of “productive“ water use. Including I and considering only shoot dry matter, WUEIT was 4.1 kg m−3. When considering shoots and roots, WUEIT increased to 4.5 kg m−3. The relation between dry matter production and IT was improved by relating IT to the potential evapotranspiration rate or the saturation deficit (Δe) of the air. As compared with other crops, WUEIT of oat appeared to be lower. This study provided evidence that normalization of IT by Δe requires the appropriate evaluation of Δe for the daylight period when transpiration occurs.