Effect of pH upper control limit on nutrient solution component and water spinach growth under hydroponics

In this study, experiment with four levels of nutrient solution pH control upper limit was conducted to explore the optimal nutrient solution pH management scheme under hydroponics by evaluating the nutrient solution characters i.e., pH, Electric Conductivity (EC), nitrate, soluble phosphorus (soluble-P), water spinach growth and quality. The results showed that the nutrient solution pH was 8.2 and unsuitable for water spinach growth under the treatment with no pH regulation during the experimental period. The pH could be maintained within a reasonable range for water spinach growth by adding nitric acid to nutrient solution. Meanwhile, the availability of cations and soluble-P were improved. The water/nutrition uptake was also promoted. Through nutrient solution pH control, the plant height, leaf number and fresh/dry shoot weight increased by 34.66-55.70%, 12.42-13.66%, 39.18-101.72% and 13.78-74.03%, respectively. It indicated that pH regulation could improve water spinach growth, promote allocation of photosynthetic product to shoot and increase the effective yield. The nitrate content of water spinach shoot increased, but which was lower than the critical value of 3000 mg/kg FW. Vitamin C content decreased under the treatment which 6.5 of pH control upper limit was set. There were no significant differences in soluble sugar and crude protein content among the four treatments. Considering the yield and quality of water spinach, the suitable nutrient solution pH control upper limit was 7.0. © 2015 Maxwell Scientific Publication Corp.