Effects of Micro-Climate in Glasshouse and Root Temperature of Hydroponic Vegetables

Abstract

Three vegetable crops were cultured in a glasshouse with two root (solution) temperatures by hydroponic culture, and planted each month from Oct. 1992 to Jun. 1994. Glasshouse and nutrient solution temperatures increased with an increase in photosynthetically active radiation (PAR). When the solution temperature exceeded 26°C, the growth rates of pak-choi (Brassica chinensis) and lettuce (Lactuca sativa) decreased with an increase in glasshouse and solution temperatures. However, when solution temperature were controlled at 21°C (winter) to 24°C (summer), growth rates of the two crops increased with PAR. The difference of the measured growth rates may be attributed to the high respiratory consumption and the low water absorption at a high temperature. In contrast, the growth rate of water convolvulus (Ipomoea aquatica) increased with an increasing PAR in both high (26°C-33°C) and low (21°C-24°C) solution temperatures. Moreover, a higher growth rate was obtained from the high solution temperature treatment.