Abstract: Two submodels were added to the developed soil vegetation atmosphere transfer model. Of the two sub models, one was the canopy photosynthesis/stomatal coupled sub model distinguishing the sun light and shaded leaves, and the second was the simplified growth sub model considering growth respiration and maintenance respiration. The comparison of measured and simulated daily evapotranspiration showed that the RMSD (root mean standard deviation) of model prediction to observation was 0.65 mm, and MAPD (mean absolute percent difference) was 14%. The daily course of the simulated and measured photosynthesis rates at the top of canopy were in good consistency. With the high resolution meteorological data, the canopy net photosynthesis and evapotranspiration were simulated over the whole growing season.The sensitivities of maximum leaf area index, environmental CO₂ concentration and leaf nitrogen content to evapotranspiration and water use efficiency were also analyzed.

Key words: water and nitrogen interaction, ammonia volatilization, winter wheat, yield.