ROOT COOLING FOR SPINACH IN DEEP HYDROPONIC CULTURE UNDER HIGH AIR TEMPERATURE CONDITIONS

In Experiment 1, the spinach plants were grown in nine nutrient solution temperature treatments ranging from 16°C to 33°C in an environment-controlled chamber to obtain basic growth data. Air temperature of the chamber was kept at 33°C in the light period and 28°C in the dark period to simulate inner temperatures of a greenhouse in hot seasons. The results showed that the treatments below 26°C had greater growth than others. The 22°C treatment had the best yield among those. This indicates that the healthy roots reduced the resistance of water transport and avoided the direct injury due to high air temperature.

In Experiment 2, the different nutrient solution temperature technique in the light and dark periods was carried out in order to save the cooling energy. As a result, yield of spinach at different cooling temperatures in the light and dark periods had almost the same as that of cooling at a fixed temperature of 22°C.

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