Energy partitioning and evapotranspiration over a rotated paddy field in Southern China

There have been recent significant changes in crop rotation and irrigation methods in paddy fields in southern China. Examining the dynamics of energy exchange and evapotranspiration (ET) in rotated paddy fields is important for better understanding of land surface processes affected by human activities. In the present study, energy fluxes, including net radiation (R-n), latent heat flux (LE), sensible heat flux (H) and soil heat flux (G) were investigated using two years (2016-2017) eddy covariance measurements from a rotated paddy field in southern China. The results showed that LE was the main consumer of R-n. Seasonal LE/R-n varied from 0.77 to 0.86 for the rice seasons, and from 0.48 to 0.51 for the milk vetch and fallow seasons. H showed an opposite seasonal trend with LE. G was higher during the milk vetch and fallow seasons because of the greater coverage of exposed soil. The high Priestley-Taylor coefficient (alpha, 1.11 +/- 0.16) and decoupling factor (Omega, 0.71 +/- 0.15) corroborated the energy-limited conditions for the rotated paddy field, indicating that R-n was the main meteorological factor governing ET. Canopy conductance (G(c)) was closely related to alpha, suggesting that daily ET was significantly affected by G(c). Vapor pressure deficit (VPD), photosynthetically active radiation (PAR) and leaf area index (LAI) played secondary roles in daily ET through their effects on G(c). ET was also affected by the wet and dry conditions of the paddy field. ET was slightly enhanced under dry conditions when LAI was low, while it decreased when LAI was large.