Tanny, J., Institute of Soil, Water and Environmental Sciences Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Cohen, S., Institute of Soil, Water and Environmental Sciences Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Grava, A., Institute of Soil, Water and Environmental Sciences Agricultural Research Organization, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Naor, A., Golan Research Institute, P.O. Box 97, Qazrin 12900, Israel
Lukyanov, V., Golan Research Institute, P.O. Box 97, Qazrin 12900, Israel

Covering crops with screens is a common practice used to attain a number of objectives like shading from supra-optimal solar radiation, sheltering from wind and hail, improving the thermal climate and exclusion of insects. Obviously the existence of a screen modifies the exchange of radiation, momentum and mass between the crop and the atmosphere and hence modifies the crop microclimate. One potential benefit of shading crops is the possibility of saving irrigation water due to the reduced radiation and wind speed. The objective of this research was to study the effect of shading screens on the microclimate of an apple orchard. For that purpose, an apple orchard in northern Israel was covered with 23 patches of screens with four shading levels, 0% (control, without shading), 16%, 30% and 60%. Screens were deployed at 4 m while tree height was 3.6 m. Air velocity near the canopy was measured by two cup anemometers one in an uncovered plot and another under a 30% shade net. Dry and wet-bulb temperatures were measured under all four shading treatments. Wind speed under the screen was 9% lower than that in the uncovered plot. The logarithmic wind speed model was approximately valid under the screens. Usually the screens reduced air temperature during the day (maximum of 1.5°C at noon) and increased air temperature at night (maximum of 0.5°C), when compared to the uncovered plot, resulting in a 2°C reduction in daily temperature range. The effect of the screens on temperature increased with increasing shading percentage, as expected. During daytime, vapour pressure deficit under the screens was lower than that in the uncovered plot but no significant effect of the screens on VPD was observed at night. Shading enhanced atmospheric stability as compared to the uncovered orchard where direct solar heating of the ground presumably induced a more unstable atmosphere. All these results suggest a potential reduction of the atmospheric water demand and possible saving of irrigation water.