Abstract: The variations of water depth and wetdry alternation in paddy field lead to the energy budget changing vertically. In this paper, an investigation was made to quantify the contribution of water depth, leaf area index and meteorological factors on energy distribution by using multiple regressions. Similar meteorological conditions and leaf area index, which can reduce the differences of energy input and canopy structure respectively, were chosen to quantify the effects of water depth on energy partitioning in a paddy field. The results showed that, with the increase of water depth, both water heat storage and water heat flux above soil layer increased, leading to a decrease in the latent heat during the daytime, especially in the period with sparse canopy. However, due to the decrease in net radiation of water surface in the period with dense canopy, the effects of water depth on the latent heat flux became small. The effect of water depth on sensible heat was not obvious, and could be ignored. The simulated results of the dualsource evapotranspiration model showed that the decrease of water latent heat with the increase of water depth was a major cause reducing the total latent heat, and this phenomenon was more obvious in the period with sparse canopy.

Key words: loessial soil, annual nitrogen fertilizer use efficiency, accumulated nitrogen fertilizer use efficiency, long-term fertilization, Loess Plateau