Effects of partial replacing NO-3-N with amino acid on yield, quality and root secretion of pakchoi (Brassica chinensis L.)

Effects of partial (20%) replacing NO-3-N with Gly, Glu and mixed amino acids in the nutrient solution on biomass, quality and root secretion of pakchoi (Brassica chinensis L.) were studied under the partial sterile hydroponics cultivation. Compared to the single nitrate treatment, the 20% partial replacing NO-3-N with amino acids could significantly reduce biomass with decreasing of nitrate and soluble starch content in the edible part of pakchoi after 24 days treatment. The nitrate and soluble starch contents in the treatment of 20% replacing of NO-3-N by Glu are lowest at 1490.8 mg/kg and 1.77 mg/g, while the contents of soluble protein, soluble sugar, free amino acid and total N in leaves and roots are improved. The treatments of partial replacing NO-3-N could change the root morphology structure and root activity, and the contents of NH+4-N, free amino acids, total organic C, total N and soluble protein are also significantly increased in the treatments of 20% Gly and 20% of mixed amino acid replacing NO-3-N. Compared to the treatment of single nitrate, the ratios of organic nitrogen to total nitrogen in the root secretions are increased by 5.6%, 11.2% and 12.8% in the treatments of 20% Gly, 20% Glu and 20% of mixed amino acids replacing NO-3-N, respectively. Therefore, partial replacement of NO-3 by amino acids could improve the quality of pakchoi, there is a negative relationship between the biomass of pakchoi and the root secretion (0.7