S06 - Session P1 - Computing crop transpiration and crop temperature

Authors: Feije De Zwart *

A well fuctioning root system and opened stomata allows greenhouse crops to evaporate large amounts of water. This evaportation contributes largely to cooling of the crop and, with it, cooling of the greenhouse air during sunny periods. Reduced transpiration or a too high crop tempertaure indicates that the crop suffers from water stress and shading might be needed. However, 'reduced' and 'too high' are relative indicators which means that measured values have to be compared with expected values. In order to provide growers insight on the energy and mass balances in the greenhouse-crop complex, a detailed study was carried out in order to parametrize the key processes of absorbtion of solar radiation and convective, radiative and latent heat release in four different greenhouse crops. The extensive and tuned model is disclosed to arbitray users by a web-interface that clearly shows the interactions between solar radiation, outside air conditions, greenhouse climate, crop transpiration and crop temperatures. The output of teh model shows what values should be considered as normal for any given condition and therefor allows to distinguish well-going crops from stressed crops.