Vapor transfer resistance in leaf-air system of crops based on micro-climate in the greenhouse

The resistance for vapor transfer in leaf-air system is important for estimating the transpiration of crops in the greenhouse by Penman-Monteith Model and managing the microclimate and determination of the irrigation schedule. The method and its principle of measuring the laminar boundary layer resistance(r_b) in the greenhouse was introduced in this paper. The measured result showed that the average of r_b was about 235 s/m and did not change with greenhouse environment. Estimating the turbulent boundary layer resistance (r_g) at different heights under different wind speeds, it is found out that r_g was much smaller than r_b during the reproductive development period of tomato and cucumber in the greenhouse, so we assumed r_e≈r_b (r_e is the external resistance). The stomata diffusive resistance (r_i) of any time scope was calculated by the model of T_l-T_a formulated based on energy and mass balance equation, simultaneously by continuously monitoring the greenhouse environmental factors. There was a good relationship between the daily transpiration of greenhouse cucumber crops measured and predicted by Penman-Monteith model. This is a useful method to get the resistance for vapor transfer in leaf-air system of crops in the greenhouse for its convenience, less-interference and succession.