LI H T, LI L, YAN Z Z, GAO C S, HAN L N, ZHANG X Y. Changes in and influencing factors of crop coefficient of winter wheat during the past 40 years on the Taihang Piedmont Plain[J]. Chinese Journal of Eco-Agriculture, 2022, 30(5): 747−760. DOI: 10.13930/j.cnki.cjea.210342
Citation: LI H T, LI L, YAN Z Z, GAO C S, HAN L N, ZHANG X Y. Changes in and influencing factors of crop coefficient of winter wheat during the past 40 years on the Taihang Piedmont Plain[J]. Chinese Journal of Eco-Agriculture, 2022, 30(5): 747−760. DOI: 10.13930/j.cnki.cjea.210342

Changes in and influencing factors of crop coefficient of winter wheat during the past 40 years on the Taihang Piedmont Plain

  • The crop coefficient (Kc) is defined as actual evapotranspiration (ET) under sufficient water supply divided by the reference crop ET (ET0), which can be calculated using meteorological factors. The Kc is used as a basic parameter to calculate the crop water requirements. The accurate determination of Kc plays an important role in optimizing irrigation management. The Kc changes with crop growth and environmental conditions. The purpose of this study was to assess how Kc varied with crop production and weather conditions by using a long-term field experiment of field management measures of winter wheat. The actual ET of winter wheat under sufficient irrigation and ET0 derived from daily meteorological parameters at Luancheng Agro-ecosystem Experimental Station of the Chinese Academy of Sciences from 1980 to 2020 were used to calculate the seasonal Kc. Additionally, the dominant factors affecting the Kc of winter wheat under the current production conditions were identified from experimental data of three recent years (2017–2020). The results showed that for winter wheat with sufficient water supply from 1980 to 2020, the average ET and ET0 were 434.7 mm and 550.8 mm, respectively. The ET0 was relatively stable, and the ET increased by 17.6%. The average Kc was 0.80 during the past four decades, with an average value of 0.76 in 1980–1990, 0.80 in 1991–2000, 0.81 in 2001–2010, and 0.84 in 2011–2020, indicating a continuously increasing trend. In the past four decades, the yield of winter wheat had increased by 42.4%, and Kc had increased by 11.6%. The increase in ET was the main reason for the increase in Kc. The ET during the past four decades increased with increasing crop production, and with a relatively stable ET0, the Kc increased. Therefore, the Kc varied with changes in crop grain production, which was related to biomass production and canopy size. Under the current growing conditions, leaf area index and biomass were important factors that affected Kc. When the leaf area index reached a certain level, Kc was mainly affected by the atmospheric evaporation potential determined by the saturated water vapor pressure difference and atmospheric temperature. The Kc during the recent three years was 0.79 for 2017–2018, 0.86 for 2018–2019, and 0.79 for 2019–2020. The average ET was 442.3 mm during the three years, and the average Kc at different growing stages of winter wheat were 0.70 from sowing to winter dormancy, 0.42 during winter dormancy, 0.76 from recovery to jointing, 1.18 from jointing to heading, 1.39 during heading to grain-fill, and 0.96 during maturity. Thus, the water requirements for winter wheat after winter dormancy increased sharply and reached the highest values during the heading to earlier grain-filling stages. The results from this study indicate that Kc varies with changes in the crop growing conditions and should not be taken as a constant value. Kc developed during three recent seasons in this study could be used to determine the crop water requirements for irrigation scheduling under the current growing conditions.
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