EVALUATION OF A GREENHOUSE CROP TRANSPIRATION MODEL WITH CUCUMBER UNDER HIGH RADIATION CONDITIONS

Authors:	E. Medrano, P. Lorenzo, M.C. Sánchez-Guerrero
Keywords:	Irrigation control, Soilless culture, Lysimeter
Abstract: Microclimate and transpiration measurements of a greenhouse cucumber crop grown in substrate were carried out during spring in 1997 in the South of Spain. Under high radiation conditions the air evaporative demand inside mediterranean greenhouses can reach greater values than outside. During May and June the mean daily global radiation was 20 MJ m^-2 d^-1. Diurnal transpiration rate was increasing from 2800 g m^-2 (LAI 1) to 4100 g m^-2 (LAI above 2), whereas night transpiration rate reached values between 120-200 g m^-2.Transpiration rate and air vapour pressure deficit (VPD) followed a linear relationship even when values were higher than 3 kPa. The use of a simplified model derived from Penman-Montheith formula, based on climate variables (solar radiation and VPD) both correlates with the canopy development (LAI, leaf area index), gave a good prediction of the hourly transpiration rate. However, for different climate conditions, crops or crop configuration, new coefficients for the particular situations should be adjusted.
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