Estimation of Winter Wheat Evapotranspiration under Water Stress with Two Semiempirical Approaches

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Journal Article
Agronomy Journal, 2004, 96 (1), pp. 159 - 168
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Winter wheat (Triticum aestivum L.) is one of most important crops in the North China Plain. However, soil water deficit (SWD) often occurs due to lack of precipitation in its growing season. In this study, we introduce two semiempirical approaches, a recharge model and the crop coefficient (Kc)-reference evapotranspiration (ET0) approach, to estimate wheat actual evapotranspiration (ETa) under no SWD and slight and severe SWD conditions. The recharge model allocated ET0to reference evaporation and reference transpiration as a function of leaf area index. In the model, ETais limited by soil water content, and crop water extraction for ETais distributed through the soil profile as exponential functions of soil and root depth. The Kc-ET0approach regarded ETaunder the SWD condition as a logarithmic function of soil water availability. Under no SWD condition, the recharge model simulated 10-d ETawith a root mean square error (RMSE) of 5.58 mm and a bias of 0.95 mm compared with measurements from a large-scale weighing lysimeter. The two approaches both estimated seasonal evapotranspiration (ET) well compared with the adjusted ET (from the soil water balance and the recharge model-simulated deep drainage). The recharge model, which simulated the seasonal ET with the RMSE of 27.8 mm and the bias of -8.0 mm, was better than the Kc-ET0approach (RMSE = 31.7 mm and bias = -33.1 mm). The seasonal pattern of soil water stress coefficient (Ks) showed that there were faster water losses at grain-filling stage than at other stages.
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