Quantifying winter wheat evapotranspiration and crop coefficients under sprinkler irrigation using eddy covariance technology in the North China Plain.

Sprinkler irrigation has been widely used for winter wheat crops in the North China Plain (NCP) to maintain high crop yield and enhance water use efficiency because water resources are scarce. Determining the accurate crop evapotranspiration (ET c) and crop coefficient (K c) of winter wheat is critical for optimizing sprinkler irrigation management. In this study, an eddy covariance system was deployed in a sprinkler irrigation field to measure the energy balance components (net radiation R n , soil heat flux G, sensible heat H, latent heat LE) and calculate ET c and K c. The wheat growth parameters and yield were also investigated. The results showed that the energy balance closure rate, the rate of daily (LE + H) to (R n - G), was 0.89, indicating a sufficient energy balance closure. Seasonal total LE flux accounted for 67% of the total available energy (R n - G). The seasonal ET c values were 434 and 396 mm during the 2019–2020 and 2020–2021 growing seasons, respectively, which are comparable to those (400–470 mm) under surface irrigation. The mean daily ET c was 0.87, 0.46, 3.24, 4.81, and 3.94 mm day−1 in the early growth, overwintering, rapid growth, middle, and late growth stages, respectively. The corresponding K c values were 0.77, 0.47, 1.09, 1.14 and 0.70. The K c values were close to those reported in the FAO 56 paper. The K c is positively related to the leaf area index (LAI), and their relationship was fitted as K c = 0.87 + 0.14 ln LAI (R 2 = 0.96) for an LAI range of 1–7, where ln is a natural logarithm function. The measured wheat grain yield was 9100 and 9857 kg ha−1, and the water productivity (WP) was 2.07 and 2.49 kg m−3 in the two seasons, respectively. Both factors are approximately 30% higher than those (7200 kg ha−1, 1.68 kg m−3) reported by other studies. Considering the high wheat yield and comparable crop ET c , sprinkler irrigation is recommended for application on the NCP. The seasonal ET c of 400–430 mm and the obtained K c values in this study can be used to make sprinkler irrigation scheduling for winter wheat on the NCP. • Wheat evapotranspiration was qualified using eddy covariance method. • Seasonal wheat latent heat accounted for 67% of total available energy. • Seasonal wheat evapotranspiration of 400–430 mm in sprinkler irrigation is comparable to that under surface irrigation. • Wheat yield of 9000–9800 kg ha−1 was investigated in sprinkler irrigation. • Sprinkler irrigation is suggested for large-scale application in North China Plain. [ABSTRACT FROM AUTHOR]