Potassium Application Rates for Tomato Grown in Soilless Culture under Hot and Humid Greenhouse Conditions

Soilless culture is the most popular cultivation method in greenhouse farming and fertigation in soilless culture determine s the qualitative and quantitatively yield of tomato (Solanum lycopersicum L.). The demand for plant nutrients vary with the surrounding environment, growing medium, and plant growth stages of the crops. Most recommended fertilizer dosages for greenhouse crops have been developed to match with the environmental conditions in the temperate region. This study attempted to identify the optimum potassium (K) fertilizer application rates for different growth stages of tomato grown in soilless culture under semi intensive greenhouse environment (31±2°C daytime temperature and 75% relative humidity). Selected dosages of K for greenhouse tomato (K treatments) were compared at advancing growth stages (0.05-0.4, 0.1-0.55, 0.2-0.6 and 0.25-0.65 g/plant/day) in a replicated trial. At the end of each growth stage, plant growth parameters and leaf tissue nutrients were assessed to compare the K application rates. Based on growth parameters, marketable yield and plant nutrient contents, the optimum K fertilizer application rates for vegetative, early reproductive, middle reproductive and late reproductive growth stages of tomato were 0.1, 0.2, 0.3 and 0.35 g/plant/da y, respectively. These application rates were able to maintain the plant tissue K concentrations of 2.5, 2.1, 2.5 and 2.8% at respective growth stages. Optimum K application rates identified in this study would be useful for making growth specific fertigation recommendations for greenhouse tomato grown in soilless culture under tropical conditions in order to make protected culture is more cost effective and environmental friendly.