Application of capillary hydroponic system to the lettuce growing under tropical climate conditions

Leaf lettuce (Lactuca sativa L., cv. Red Fire) was grown by Capillary hydroponic system without electricity use to improve the system for tropical climate conditions. The polyester capillary mat was put on the floating styrol board (with or without slope) and covered with substrates originated in tropical countries (rice husk, rice husk charcoal and coconut coir) with or without mulching film. The seedlings were transplanted on the capillary mat and the root system was covered with substrates. Mulching film and the slope of floating board did not affect the yield and quality of lettuce. Rice husk charcoal was found to be the best substrate in spring and autumn, while coconut coir was found to be the best in summer. Tip-burn symptom was found in the plants grown in newly used coconut coir. But the symptom disappeared by using reused coconut coir and plants performed better than using rice husk substrate. We concluded this system is one of feasible hydroponic methods for leaf vegetable production under tropical conditions. The appropriate control of nutrient solution was also discussed.