Effect of coconut coir media on bitter gourd (Momordica charantia L.) growth and yield in an energy-saving hydroponic system

The effects on the growth and yield of bitter gourd of an energy-saving hydroponic system consisting of coconut coir media, in which power-driven circulation of a nutrient solution was not installed were investigated using full (standard) and half-strength commercial nutrient solutions, compared with rockwool media. The changes in the nutrient concentrations in the growth media, chemical characteristics such as fixation (adsorption) or release of nutrients by/from the media and physical characteristics were also examined. The vegetative growth of the plants was not affected by the media or the strength of the nutrient solution. The yield of marketable fruits per plant was higher with the use of a half-strength nutrient solution in the coconut coir media than with that of a half-strength solution in the rockwool media. Fruit number per plant was lower with the use of a half-strength nutrient solution in the coconut coir media than with that of a full strength solution. The fruit quality (fruit length) was not affected by the strength of the nutrient solution. The concentrations of all the mineral nutrients of the coconut coir media supplied with a full strength solution showed a five to nine fold increase, compared with those in the nutrient solution supplied at the time of vigorous plant growth. Although the potassium concentration in the coconut coir supplied with the half-strength solution showed a two fold increase, the concentrations of nitrogen and phosphorus decreased. Release of potassium from the coconut coir media was confirmed in the laboratory experiment. The nutrient concentrations of the leaves were higher than those reported for the leaves of the plants cultured in soil, except for the concentration of nitrogen. Thus, we concluded that the use of a half-strength nutrient solution was suitable for the energy-saving hydroponic system in bitter gourd cultivation. However, for continuous reuse of the coconut coir media, further trials should be conducted to maintain stable levels of nutrients and to re-adjust the nutrient concentrations in the media.