典型半干旱区干旱胁迫作用对春小麦蒸散及其作物系数的影响特征

Abstract

An understanding of evapotranspiration, which is an important component of the surface water cycle, is critical in water resource management and planning, and in meeting the water requirements of agriculture and ecological systems. Although the methods for calculating crop evapotranspiration are advanced in humid areas, the understanding of evapotranspiration in semi-arid areas is developing because evapotranspiration is significantly affected by drought. The classic crop evapotranspiration model and crop coefficients cannot be applied to estimations of actual evapotranspiration, which is rarely studied now. In this study, we analyzed differences between lysimeter evapotranspiration and evapotranspiration that was estimated with Food and Agriculture Organization (FAO)-recommended crop coefficients. In addition, changes in evapotranspiration according to the degree of drought stress were analyzed with lysimeters, evaporating dishes, ultrasonic and eddy instruments, and conventional meteorological data in spring wheat fields in typical semi-arid zones of the Dingxi arid ecological environment comprehensive scientific experiment station, which is located in the Loess Plateau. The variations in spring wheat reference evapotranspiration/pan evaporation and actual evapotranspiration/pan evaporation according to the degree of drought stress and the effects of drought stress on the spring wheat crop coefficients in this area were studied. Because crop evapotranspiration is significantly affected by drought stress in semi-arid areas, the differences between lysimeter evapotranspiration and evaporation that was estimated with FAO-recommended crop coefficients were very significant. Crop coefficients were highly dependent on drought stress, and this dependence increased according to the reduction in the degree of drought stress. In addition, its sensitivity was significantly lower after the drought stress reached about 0.7. In this study, crop coefficients that were modified during the crop development and exuberant period were far below the FAO-recommended values and the Kumar correction values. The modified crop coefficients were obviously closer to the actual observed values than the spring wheat evapotranspiration values that were estimated using other crop coefficient. The coefficient of linear fitting of the modified crop coefficient and the observations was 0.98. The coefficient of determinationwas 0.45, and the standard error was 0.85. Therefore, the modified crop coefficient was effective for estimating crop evapotranspiration in semi-arid areas.