|Authors: ||U.N. Mutwiwa, H.J. Tantau, V.M. Salokhe|
|Keywords: ||Phytomonitoring, tomato, natural ventilation, NIR pigments, fan and pad cooling|
In the humid tropics, high temperature and relative humidity inside greenhouses are the main factors that hinder conventional vegetable greenhouse cultivation.
The use of fan and pad cooling systems, application of near infra red (NIR) reflecting pigments on the roof cover and increasing the area of ventilation openings are some of the attempts that have been made to overcome this problem.
The fixing of insect proof screens in front of the ventilation openings prevents the entry of some insect pests into the greenhouse but at the same time, decreases the ventilation efficiency.
The use of NIR reflecting pigments decreases air temperature but alters the spectral transmission of the greenhouse cover.
In this research, the effects of spectral modification (using NIR reflecting pigments), natural and forced ventilation (evaporative cooling) on the growth of tomato plants, Lycopersicon esculentum (Miller) `FMTT260´, were investigated by online measurement of plant responses (phytomonitoring), in greenhouses located at the Asian Institute of Technology, Bangkok, Thailand.
Results show clear differences in the way plants responded to different greenhouse microclimates.
In the warm season, the NIR reflecting pigment significantly reduced the air temperature, leaf transpiration and the net photosynthesis inside the greenhouse, but the differences were small in the cool season.
The fan and pad cooling system reduced both transpiration and temperature (air and leaf) but had minimal effect on net photosynthesis in the cool season.
Fairly good correlations were obtained between net photosynthesis and the intensity of global radiation inside the greenhouses.
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