Seasonal and Interannual Variations in the Surface Energy Fluxes of a Rice–Wheat Rotation in Eastern China

Quantitative knowledge of the water and energy exchanges in agroecosystems is vital for irrigation management and modeling crop production. In this study, the seasonal and annual variabilities of evapotranspiration (ET) and energy exchanges were investigated under two different crop environments – flooded and aerobic soil conditions – using three years (June 2014 to May 2017) of eddy covariance observations over a rice–wheat rotation in eastern China. Across the whole rice-wheat rotation, the average daily ET rate in the rice paddies and wheat fields was 3.6 mm d–1 and 2.4 mm d–1, respectively. The average seasonal ET was 473 and 387 mm for rice and wheat fields, indicating a higher water consumption for rice than for wheat. Averaging for the three cropping seasons, rice paddies had 52% more latent heat flux than wheat fields, whereas wheat had 73% more sensible heat flux than rice paddies. This resulted in a lower Bowen ratio in the rice paddies (0.14) than in the wheat fields (0.4). As eddy covariance observations of turbulent heat fluxes are typically less than the available energy (Rn − G, i.e., net radiation minus soil heat flux), energy balance closure (EBC) therefore does not occur. For rice, EBC was greatest at the vegetative growth stages (mean: 0.90) after considering the water heat storage, whereas wheat had its best EBC at the ripening stages (mean: 0.86).