ISHS Acta Horticulturae 578: International Symposium on Design and Environmental Control of Tropical and Subtropical Greenhouses
GREENHOUSE ENVIRONMENT AND LEAF LETTUCE CULTIVATION DURING HOT SUMMER SEASON IN SOUTH KOREA |
| Authors: | S.-W. Nam, Y.-C. Yoon |
| Keywords: | cooling, nutrient solution, assistant cooling, greenhouse environment, transpiration rate, absorption rate |
| DOI: | 10.17660/ActaHortic.2002.578.52 |
| Abstract:
During hot summer season in South Korea, about 21.6% of the greenhouse farms are in fallow state and even most of greenhouse farms to be cultivated are operated under the very poor environmental conditions. When the summer greenhouses are cooled with the evaporative cooling system together with shading screen, they can mostly be maintained below 35o, which are about 3.6~4.4oc lower than those operated with natural ventilation system only. But when the each assistant cooling methods, such as vent, vent and shading screen, roof sprinkling are used for greenhouse cooling, about 74.8%, 26.9%, and 58.2% of the temperatures measured from 10:00 to 17:00 every day during July to August were above 35oc and the maximum temperature was increased up to 42oc. The method of cooling the nutrient solution in combination with spraying water on leaf surface during summer season was found to be successful. The greenhouse, equipped with shading screen and utilized for this experiment, was exposed to the summer climate under the air temperatures of 33~35oc and the relative humidity of 60~73%. When the nutrient solution was cooled down to 20oc and also the water was sprayed over plant canopy, the temperature of leaf lettuce was found to be 30~32oc which was about 5oc lower than the temperature(35~37oc) of leaf lettuce grown under control greenhouse with no treatment of cooling. In case of leaf lettuce in control greenhouse, the transpiration rate of leaf surface at this time was higher than the water absorption rate of root, which was explaining why the leaf lettuce was subjected to withering state and the leaf temperature was increased so high. The difference between transpiration rate and absorption rate were measured about 4.1~7.5 mg.cm-2.h-1, which could be good measure to express why and how much the root activity of leaf lettuce were reduced. | |
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