ISHS Acta Horticulturae 751: IV International Symposium on Rose Research and Cultivation
THE EFFECT OF COVERING MATERIAL ON THE MICROCLIMATE OF ROSE PLANTS IN A GREENHOUSE |
| Authors: | E. Mashonjowa, J.R. Milford, J.G. Pieters, H. Uchida Frausto |
| Keywords: | radiometric properties, leaf temperature, dynamic greenhouse climate model, transmittance, Gembloux Dynamic Greenhouse Climate Model |
| Abstract:
Measurements of the radiometric properties of plastics used as covering materials of horticultural greenhouses in Zimbabwe were made, both under laboratory conditions and in an operational greenhouse. The magnitude of the changes in available solar radiation due to the use of different covering materials and their effects on leaf temperatures are presented using a dynamic greenhouse climate model. Transmittances in the whole solar and PAR bands under laboratory conditions were similar, ranging from 60% to 85%, while those in the thermal infrared ranged from 20% to 60%. Transmittance values found in the greenhouse were similar to those found for horizontal sheets under laboratory conditions. In order to generalise on the effects of different plastics on actual leaf temperatures, the Gembloux Dynamic Greenhouse Climate Model (GDGCM) was used to simulate air temperature and humidity, leaf temperature and the solar radiation at the top of the canopy using climatological observations and the radiometric properties measured under laboratory conditions as inputs. The model gave values of up to - 5°C and + 1°C for the extreme leaf to air temperature differences close to midday and sunrise, respectively. The model showed that the microclimate under photoselective polyethylene films was comparable to that under glass and that the range of available plastics gave little differences between daytime leaf-air temperature differences for all films, but could change the minimum temperature by up to 1°C. Aging of plastic films of up to 3 years was found to have a negligible effect on the plant microclimate. The measurements made during the project, together with the use of a greenhouse climate model, provide quantitative estimates of the effect of different covering materials on the radiation available to plants within a greenhouse, and also of their influence on leaf-air temperature differences under conditions typical of horticultural operations in Zimbabwe. | |
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