Evapotranspiration of typical agroecosystems in the North China Plain based on single crop coefficient method

The crop coefficient method recommended by FAO56 is a method to calculate the actual evapotranspiration of crops, which can simply and accurately reflect the evapotranspiration patterns and characteristics of different agroecosystems during different growth stages. Although the crop coefficient method is widely used, there are still some problems in applying this method in the North China Plain. Research on a single agroecosystem of winter wheat-summer maize has been conducted for a long time. However, there is a lack of systematic and comprehensive research on the evapotranspiration patterns of various typical agroecosystems in the North China Plain through the single crop coefficient method. Therefore, it is difficult to provide quantitative theoretical support for water consumption management and planting structure adjustment. Furthermore, the variation in crop coefficients for the typical pear orchard agroecosystem, the main fruit and the most important economic crop in the North China Plain, is urgently needed. In this study, the crop coefficients and evapotranspiration patterns of different growth stages of irrigated crops in the typical agroecosystems of winter wheat-summer maize farmland, cotton field, and pear orchard in the North China Plain were examined and verified from 2016 to 2017. The entire growth stage was divided into initial, developing, mid, and end stages based on the crop growth stages and physiological characteristics. According to the single crop coefficient method recorded in FAO56 manual, the average crop coefficients of the initial, developing, mid, and end stages of different crops were 0.60, 0.88, 1.07, and 0.72 for winter wheat; 0.46, 0.76, 1.01, and 0.80 for summer maize; 0.34, 0.71, 1.07, and 0.78 for cotton; 0.81, 0.91, 1.02, and 0.96 for pear trees, respectively; while the calculated actual evapotranspiration was 694.3 mm, 472.2 mm, and 825.7 mm for the above three ecosystems, respectively. Evapotranspiration measured by the eddy covariance systems was 701.4 mm, 496.5 mm, and 763.5 mm for winter wheat-summer maize, cotton field, and pear orchard agroecosystems, respectively. Both the calculated and measured actual evapotranspiration values of the four crops showed a single-peak change from the initial to the end stages, with the same trend. The correlation coefficients between the calculated and measured evapotranspiration for all three agroecosystems were greater than 0.8. The calculated actual evapotranspiration values compared to the measured values during the growth stage of winter wheat-summer maize, cotton, and pear orchard agroecosystems were 1.0% lower, 4.9% lower, and 8.1% higher, respectively. This study not only provided the crop coefficients of wheat, maize, and cotton but also filled the gap in the research on crop coefficient of pear trees in this region. It is particularly important that this study used the observed evapotranspiration by the eddy correlation system to verify the calculated evapotranspiration using the single crop coefficient method at the same spatial and temporal scale, which shows the applicability of the calculated crop coefficients in the region. The applicability of the single-crop coefficient method in different agroecosystems in the North China Plain was clarified. This research provides a scientific basis for making reasonable irrigation plans and achieving precise management of crop water consumption.