Studies on the Windbreak Nets

Abstract

In order to investigate the micrometeorological modification of cool weather damage by use of 2-m high cheese cloth and PE russell windbreak nets in paddy rice fields, the author carried out the meteorological observation and growth measurement during periods from June to August in 1979 in Naganuma, Hokkaido.The weaker region of relative wind speed was from 1 to 5H (distance expressed in net height) leeward and the relative wind speed for cheese cloth net was generally 10% smaller than that of russell net. The maxima of surface water and leaf-stem temperatures were in 2 to 5H and the effective range in -5 to 20H. The cheese cloth net was more efficient than russell net in the highly affected range at 2, 3.5 and 5H. Because of the convergence and divergence winds through an opening at the bottom of the nets, the temperatures at 1H were generally lower than those at -2.5 and 2H. The warming effect on clear or fine days was larger than that on cloudy or rainy days. It was also recognized even in the night of cloudy or rainy days. Surface leaf-stem temperature increased faster and higher than surface water temperature in the early morning on clear day because of specific heat and heat capacity differences of water and leaf-stem.The effective range on rice plant length was from -5 to 35H for cheese cloth net and -5 to 20H for russell net. The plant length was fairly high in 1 to 5H for both the nets. It is effective to grow grasses in the 25-cm open space under nets in order to protect paddy rice plants near nets.