Effects of nitrogen and calcium nutrition on safety quality and anti-oxidative enzyme activities of spinach

A hydroponic experiment was carried out to study the effects of nitrogen and calcium nutrition on the growth, safety quality and antioxidative enzyme activities in spinach. Results showed that spinach achieved the highest biomass at the rate of 12 mmol/L N supplied with the same rate calcium. With the same N supply, spinach achieved higher yield when 5mmol/L Ca2+ was supplied. Nitrate content and Ca2+ concentrations in edible parts of spinach increased with N. At 8mmol/L N concentration, soluble oxalate content in edible parts of spinach was lowest, while total oxalate was lowest with 5 mmol/L Ca2+. With the same N supply, POD activities of spinach leaves were lowest supplied with 5mmol/L Ca2+. SOD activities of leaves were highest when N concentration was 8 mmol/L and Ca2+ level was 5mmol/L. CAT activities markedly decreased when N and Ca2+ concentrations were increased with the same N level. Supplied with the same calcium concentrations, MDA content increased with the increase of N concentrations, while MDA content of 5 mmol/L Ca2+ was the lowest with the same N supply. Proline contents in leaves increased markedly when Ca2+ concentrations were increased and those of low N treatments were lower. In conclusion, 8 mmol/L N and 5 mmol/L Ca2+ were the proper concentrations of N and Ca nutrition for the growth of spinach based on results from this experiment.