DEVELOPMENT OF A DYNAMIC PLANT SURFACE MICROCLIMATE MODEL (PSCLIMATE) FOR GREENHOUSE VEGETABLES

Based on the principle of energy balance and the heat and mass transfer theory, a one-dimensional plant surface climate model (PSCLIMATE) has been developed for greenhouse vegetable plants. This model uses parameters that describe characteristics of the greenhouse structure and the plant canopy together with routine climate observations above the canopy, to predict in canopy and leaf surface microclimate. The output of the model includes vertical profiles of solar irradiance, air temperature and relative humidity, and the temperature, vapour pressure deficit and wetness at the leaf surface. The default plant of this model is cucumbers and the model has been validated using microclimate data collected in a greenhouse cucumber experiment over a fall growing season in 1996. It predicted precisely the in-canopy air temperature and relative humidity, as well as temperature and wetness at leaf surfaces in most cases. The model overestimated air temperature in the lower canopy when air temperature exceeded 22°C and forced ventilation was in operation. The dynamic model was further expanded to greenhouse tomato (PSCLIMATE-Tomato) in 2002-2003. Physiological parameters of tomato plants, architectural parameters of tomato canopy, and wind speed profile within the canopy determined from references and measured values were used in this model. Microclimate data collected in a greenhouse tomato experiment in the winter 2002-2003 were used to validate the model. The model correctly predicted microclimate variables within canopy and at leaf surface although some deviations from observed values at noontime on sunny days, when solar irradiance was very high, were found.