This study investigated greenhouse and plant surface microclimate for cucumber crops (Cucumis sativus) under high pressure overhead fogging. Overhead fogging maintained greenhouse humidity above its set point and avoided excessively low humidity conditions on sunny days. Fogging caused minimal to moderate changes in greenhouse air temperature in the fall depending on whether or not the leaves were sunlit or shaded. The temperature of sunlit leaves decreased by 1 to 1.5 °C (1.8 to 2.7 °F) under occasional fogging in the morning and by 3 °C (5.4 °F) under extensive fogging during noon hours. The temperature of fogged shaded leaves did not significantly change (<1 °C) when compared to nonfogged shaded leaves. Leaf wetness duration (LWD) was extended when overhead fogging was used. The length of extended daytime wetness duration (LWDday) from 0800 to 1700 HR in the fogged greenhouse depended primarily on global radiation at the leaf level. A simulation model was developed to predict LWDday using daily integrated global radiation (Rsum) as the input.
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