|Authors: ||U.N. Mutwiwa, B. von Elsner, H.J. Tantau, J.F.J. Max|
|Keywords: ||Insect-proof screens, natural ventilation, NIR-reflection, tropics|
High temperatures and humidity inside greenhouses located in the tropics is one of the major constraints to protected cultivation in areas such as central Thailand.
Studies were conducted in two naturally ventilated greenhouses, clad with insect-proof nets on the sidewalls and roof ventilation openings, to investigate the effect of near infra red (NIR) reflecting pigments on the greenhouse microclimate and plant growth.
A polyethylene film was used to cover the roof and gable of the greenhouse while a white plastic film was used as a mulching material.
A shading paint containing a NIR-reflecting pigment (ReduHeat, Mardenkro B.V., Baarle-Nassau, The Netherland) was applied on the roof of one of the greenhouses ("Trt"). This led to the lowering of the greenhouse air temperature by up to 4°C when the crop was young corresponding to 18% reduction in transmission of global radiation.
However when the crop was mature at 57 days after transplanting during the rainy season, transpiration cooling minimised air temperature differences between the two greenhouses.
Shading reduced plant water requirement, power consumption of the fans, the number of blossom-end rot affected and parthenocarpic fruits, in both dry and rainy season.
A slight reduction in marketable yield and an increase in the number of cracked fruits were observed in Trt.
The results reveal that combination of natural ventilation and NIR-reflection may provide a solution for cooling greenhouses in areas with high ambient humidity and high solar radiation levels.
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