PLANT GROWTH OF COCO-PEAT GROWN TOMATO UNDER ENHANCED FERTIGATION IN HOT AND HUMID CLIMATES

The effects of method and volume of fertigation, with or without adjustments in electrical conductivity (EC) were examined for grow-bag culture of tomato (Lycopersicon esculentum Mill.) under two levels of greenhouse micro-climates. The two climatic regions selected for the experiment were different with respect to temperature and humidity. The moderately hot climate maintained a mean temperature of 29.2±3.7°C and RH of 65.6±4.7% in the greenhouse air while the same in the hot and dry climate were 33.5±4.2°C and 54.2±6.7%, respectively. A variable volume of water availability was imposed on growing plants by modifying the volume applied, method of supply (i.e., circulation culture) or water holding capacity of the medium. With respect to shoot and root growth, the standard fertigation volume (0.5 L plant^-1 day^-1), was adequate only during the vegetative growth whereas the evapo-transpiration (ET) based adjustments in fertigation volume (0.8-1.5 L plant^-1 day^-1) contributed to maintain shoot growth during the reproductive stage specially under moderately hot climate. The latter increased root growth when drainage and aeration were enhanced by sandwiching a sand layer within the medium under the same greenhouse climate. There was no significant improvement in most shoot and root growth parameters when the irrigation volume was further increased (1.0-2.0 L plant^-1 day^-1) and circulating the drainage collection (three times a day) while keeping EC similar to the control at both climatic regions. Hence, the plant water requirement of tomato grown under varying degree of hot and humid conditions in tropical greenhouses can be successfully met by increasing the supply volume of fertigation during reproductive stage (at 12-20 WAP) to 985-1456 ml plant^-1 day^-1. Enhanced water and EC management through circulation culture is a better option for this purpose.