Abstract
To improve the yield of greenhouse cucumbers in Japan, we investigated the effects of environmental elements on yields of cucumber grown in environmentally controlled greenhouses. Several cultivars of the cucumber were grown in 2 greenhouse compartments. In the conventional compartment, only the air temperature was controlled. In the controlled compartment, the air temperature, humidity, and CO2 concentration were controlled. In total, 3–5-month experiments were conducted 6 times for 3 years, and yields were compared between the conventional and controlled greenhouses. Although air temperatures were controlled at the same settings in both greenhouses, in half of the experiments, the temperatures differed significantly between the conventional and controlled greenhouses. Relative humidity and humidity deficiency in the controlled greenhouse were significantly higher and lower, respectively, than those in the conventional greenhouse. The CO2 concentration in the controlled greenhouse was significantly higher than that in the conventional greenhouse in 3 experiments conducted in the winter season. Cucumber yields in the controlled greenhouse were significantly higher than those in the conventional greenhouse in 4 experiments but there was no difference in 2 experiments. The yield was strongly correlated with average daily solar radiation in the greenhouses. The yield per unit solar radiation was positively and strongly correlated with the daytime CO2 concentration in the greenhouses. Thus, the controlled CO2 concentration improved the yield in the controlled greenhouse. However, there was no significant correlation between the yield per unit solar radiation and relative humidity or humidity deficit.
