Co-Authors:
Tanny, J., Institute of Soil, Water and Environmental Sciences, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel
Teitel, M., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P.O.B. 6, Bet Dagan 50250, Israel
Barak, M., Institute of Agricultural Engineering, Agricultural Research Organization, Volcani Center, P.O.B. 6, Bet Dagan 50250, Israel
Esquira, Y., SHAHAM, Extension Service, Ministry of Agriculture and Rural Development, P.O. Box 28, Bet Dagan 50250, Israel
Amir, R., SHAHAM, Extension Service, Ministry of Agriculture and Rural Development, P.O. Box 28, Bet Dagan 50250, Israel
Abstract:
Covering crops with screens is a common practice used to attain a number of objectives: shading from supra-optimal solar radiation, sheltering from wind and hail, improving the thermal climate and exclusion of insects. Obviously the existence of a screenhouse modifies the crop microclimate. Screenhouses of different heights are used by different growers for the same crop. This is mainly due to the limited information on the effects of the different heights on the microclimate. Thus, the objective of this research was to investigate the effect of screenhouse height on several microclimatic parameters. Measurements were conducted in two adjacent, otherwise very similar screenhouses of different roof height: 4 m and 2 m in which Ornamental Ruscus was grown. The following parameters were measured in each house, approximately at its center: dry- and wet-bulb air temperature by four sensors, leaf temperature and net radiation. Results show that net radiation was almost identical in the two houses. Air temperature and vapour pressure deficit near the plants, as well as leaf temperature, were higher in the lower screenhouse than those measured in the higher one. The average daily air temperature difference and leaf temperature difference between the two houses were 1.5°C and 1.1°C respectively. The vertical temperature gradient within the lower screenhouse was about 3 times larger than that within the higher screenhouse, due to the better air mixing in the latter than in the former and the movement of warm air to higher levels in the higher screenhouse than in the lower one. Most of the time, absolute humidity in the higher house was closer to the outside absolute humidity than that in the lower house. In conclusion, this study indicated on enhanced mixing and ventilation of the air near the plants in the higher screenhouse as compared to the lower one.
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