Experimental and numerical studies on the heterogeneity of crop transpiration in a plastic tunnel

The heterogeneity of crop transpiration is important to clearly understand the microclimate mechanisms and to efficiently handle the water resource in greenhouses. A computational fluid dynamic software (CFD2000) was used to study the climate and crop transpiration distributions in a 22 x 8 m(2) plastic tunnel situated in Avignon, France, together with a global solar radiation model and a crop heat exchange model. The distribution of solar radiation within the greenhouse tunnel was determined based on the path of the sun, the greenhouse geometry, the cover transmittance and the sky conditions. The crop transpiration was deduced by assimilating the crop to a porous medium exchanging latent and sensible heats with its environment. The radiative and convective heterogeneity in two vertical sections of the tunnel predicted by the CFD model was validated against the experimental results obtained by a group of solar cells and sonic anemometers. The validated model was finally used to predict the transpiration flux of a mature lettuce crop in the tunnel. The crop transpiration strongly varied (up to 30%) according to the place in the tunnel. The predicted crop transpiration was in close agreement with the measured value both along the sections with the side openings and between the consecutive openings. (C) 2002 Elsevier Science B.V. All rights reserved.