Spatial variability of air-humidity inside naturally ventilated tropical greenhouse
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Agricultural Systems and Engineering, Asian Institute of Technology, P.O. Box 4, Klong Luang, Pathumthani 12120, Thailand
Institute of Horticultural and Agricultural Engineering, Hannover University, Herrenhäuser 2, D-30419 Hannover, Germany
Int. Agrophys. 2005, 19(4): 329-336
Research was conducted in four net-greenhouses with tomato crop inside, to study the spatial distribution of air-humidity under naturally ventilated conditions. Both, absolute and relative stress-gradients of air-humidity were observed for vertical (z) and horizontal (x and y) directions with x as semi-minor axis of 3 m x 6 m greenhouse structure. Four greenhouses with 53, 34, 33 and 19% porosity HDPE nets were used with two plant maturity stages and two plant density levels. Shorter plants occupied 5% of gutter height while taller stature 50%; plant density doubled from 1.7 to 3.3 plants m-2 with three and five rows kept parallel to y axis respectively. It was observed that specific humidity gradients in vertical (z) direction increased by 30% with vegetation. Lowering porosity increased vertical humidity gradient. Horizontal (x) locations exhibited 25% humidity gradients that increased with vegetation. However, it decreased with less porous nets. About 30% horizontal (y) humidity gradient was noted, which decreased with vegetation but lowering porosity increased it from 10 to 25%. Horizontal gradients responded considerably slowly towards plant density, rather they were found to be more sensitive to plant height. Plant density, on the other hand, altered their peak absolute values. With matured plants inside, less porous greenhouses evidenced lesser evapotranspiration values.
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