URBANUS N. MUTWIWA1, JOHANNES MAX2, HANS JURGEN TANTAU1
1Leibniz Universität Hannover, Institute of Biological Productions Systems, Biosystems and Horticultural Engineering Section, Germany
2Asian Institute of Technology, Protected Cultivation Project, Thailand
Cooling greenhouses in the humid tropics is especially challenging due to the high intensity of solar radiation and humidity prevalent in these regions. The effect of natural ventilation and evaporative cooling on the greenhouse microclimate, growth and production of tomato Solanum lycopersicum cv FMTT260 were evaluated. The research was carried out in two greenhouses (measuring 20m long by 10m wide) at the experimental site of the ``Protected Cultivation Project'' on the campus of the ``Asian Institute of Technology'' (AIT), situated 44 km north of Bangkok in Khlong Luang, Pathum Thani, central Thailand, (14 04' N, 100 37' E, altitude 2.3m). The naturally ventilated greenhouse was covered with a UV-absorbing plastic film on the roof and a 50-mesh insect proof net on the sidewalls and roof ventilation opening. The evaporative cooled greenhouse was completely covered with the UV-absorbing plastic film and was equipped with a fan and pad cooling system. In each greenhouse, 300 tomato plants were grown at a density of 1.5 plants m-2 and maintained for 15 to 20 weeks. Results from two seasons show that the cooling method influenced the greenhouse microclimate, plant growth and yield. Although evaporative cooling lowered greenhouse temperature, the unwanted increase in humidity resulted in fungi infections and reduced transpiration. Plants grown in evaporatively cooled greenhouse were 30cm to 45cm shorter than those grown in naturaly ventilated one. Differences were also noted in flowering, leaf area, dry matter partitioning and harvested yield. The significance of cooling method and greenhouse covering material on plant growth and production in protected cultivation systems in the tropics is discussed.
Keywords: Evaporative cooling, greenhouse, microclimate, natural ventilation, tomato