Effects of Environmental Factors on Evapotranspiration of Greenhouse Cucumber Crops in Hydroponic Culture

Abstract

The amounts of the daytime and nighttime transpiration of greenhouse cucumber crops in hydroponic culture and of the evaporation from the gravel pots were determined by measuring the nutrient solution uptake and the increase in fresh weight of the crop.The experiments were conducted during the period from October 11 to December 7 in 1980 for the mature cucumber crops.The solution uptake expressed as the decrease in level of the solution in a solution storage tank was measured using an accurate level meter with micro-processor controlled pulse motor.Average daytime evapotranspiration was 0.74l/plant/day. During the daytime, 34% of the transmitted solar radiation was converted into latent heat by evaporation, on average.A stepwise multiple regression analysis showed that daytime evapotranspiration can well be expressed by a linear equation of solar radiation and average daytime saturation deficit of the air.During the night, average transpiration was 0.10l/plant/nighttime and average evaporation from the gravel pots was 0.08l/plant/nighttime; the average evapotranspiration being 0.18l/plant/nighttime. For this evapotranspiration, about 10-20% of the total nighttime heat input for the greenhouse heating was consumed.