A greenhouse crop production system for tropical lowland conditions

Key words: tropical lowland climate, tropical lowland greenhouse, plastic greenhouse, near infrared radiation (NIR) reflecting plastic, greenhouse climate model, determinate tomato, crop growth, development, truss appearance rate, crop simulation model, INTKAM. The goal of this research was to improve greenhouse crop production under tropical lowland conditions. The dynamics of greenhouse climate were analyzed using a simple greenhouse climate model (GCM), while the growth and development of a determinate tomato crop were quantified using the INTKAM greenhouse crop simulation model. By combining the GCM and INTKAM models, ways to improve tomato production under tropical lowland greenhouse were investigated. Model calculations were calibrated and validated with experiments in six prototype greenhouses with three different near infrared (NIR) transmissivities during three periods with different tropical lowland climate characteristics. The greenhouses having high natural ventilation capacity showed a climate closely coupled to the outdoor climate. Greenhouse air temperature TAir was affected more by variation in ventilation and leaf area index than by the applied NIR transmission. Simulation shows that lowering TAir can be achieved by: (i) reducing near infrared radiation (NIR) transmission especially for bigger greenhouses and humid conditions, (ii) increasing ventilation openings and (iii) transpiration cooling, especially under hot and dry conditions. GCM study indicated that naturally ventilated model greenhouses of up to size of 14400 m2 were capable to create TAir close to or lower than outdoor air temperature Tout when the greenhouse crops had leaf area index of higher than 0.5. Crops with low number of trusses produced substantially lower fruit weight than crops with high number of trusses. Determinate tomato clearly exhibit high fruit abortion, with the number of fruits per truss decreasing as truss number increases. This partly can be explained by low source – sink strength ratio during the productive period. Effort to increase tomato production might require adequate crop management aimed at finding the appropriate source – sink balance. Scenario studies revealed that fruit production by a determinate tomato crop can be increased slightly by using zero NIR transmittance plastic film and by planting three crops per year (which is current practice). However, when the number of fruits can be maintained constant through appropriate crop management measures, the production would increase with increasing fruit load and the lengthening production period through fewer plantings per year.