Simulation of greenhouse management in the subtropics. I. Model validation and scenario study for the winter season

Adaptation of greenhouse climate management strategy to local climatic conditions is very important for the improvement of resource use efficiency of greenhouse crop production. The objective of this study was to explore alternatives to the existing Venlo-type greenhouse climate control policy under Chinese subtropical climate conditions, through simulation analysis using the Greenhouse Process (KASPRO) model. Experiments were carried out in a Dutch Venlo-type glasshouse on a farm in Shanghai (31.3 degrees N, 121.4 degrees E), to collect climate and crop data to validate the model. The results show that using outside hourly weather data as inputs, the KASPRO model generally gives satisfactory predictions of greenhouse air temperature and humidity, and of canopy transpiration rate under both summer and winter climate conditions for subtropical China. After the model validation, scenario studies were carried out to investigate the possible responses of crop biomass production and energy consumption to different nighttime and daytime air temperature set points and canopy size based on leaf area index (LAI), under the winter climate conditions typical of subtropical China. The scenario analysis shows that, during winter, the highest biomass production is achieved when the daily mean air temperature in the greenhouse is 19.7 degrees C, which is realised when day and night air temperature set points are 23 and 18 degrees C, respectively. The highest energy use efficiency for biomass production is achieved when daily mean air temperature in the greenhouse is 18 degrees C, which is realised by setting the set points of air temperature at 19 and 15 degrees C, respectively. During winter, crop biomass production reaches the maximum at a LAI of 3. The energy consumption increases with the canopy LAI. It is concluded that both from the biomass production and energy saving point of view, an air temperature set point of 19 degrees C for daytime and 15 degrees C for nighttime and a canopy LAI of 2-3 provides the most energy-efficient conditions for greenhouse cucumber crop production under the winter climate conditions in subtropical China.