Combined application of nitrogen and sulfur improving quality of substrate culture garlic bulbs

Garlic (Allium sativum L.) was among the earliest cultivated crops, has been planted all over the world. Allicin and garlic polysaccharide are important active ingredients in garlic, which have been popular in medicine, health and functional food. The S fertilization has already been shown to have a strong influence on the formation of S containing secondary metabolites in crops. Along with nitrogen metabolism in the metabolic process of sulfur, so there is synergistic effect between sulfur and nitrogen. The aim of this study was to analyze the response relationship between the garlic quality and the nitrogen and sulfur interaction, and to evaluate the comprehensive quality of garlic bulbs by the method of membership function, a pot experiment was conducted by using three levels N and S applied in factorial combinations of 5, 10, 20 mmol/L and 2, 4, 8 mmol/L in vermiculite and pearlite culture. The results indicated that the main inclusion reacted differently in response to N and S levels. N or S single factor had no significant effect on content of soluble protein, VC, garlic polysaccharide, free amino acid, while S had significant effect on allicin. The influence of N, S single factor on garlic quality was far lower than that of the interaction of N and S. The quality of garlic bulbs was raised to different extents by nitrogen and sulfur fertilization, and the interaction of nitrogen and sulfur had a significant effect on the quality formation of garlic. When N concentration was 10-20 mmol/L, sulfur concentration had significant effect on allicin content of garlic bulbs. The content of allicin was increased significantly as the increase of S levels under 4.0 mmol/L, but decreased when the sulfur content reached at 8.0 mmol/L, which showed that high content of sulfur element could inhibit the synthesis of allicin. Content of garlic polysaccharide was promoted by increasing nitrogen or sulfur fertilization. However, it would be inhibited when the nitrogen content exceeded to 10.0 mmol/L or the sulfur content reached at 8.0 mmol/L. Content of polysaccharide was the highest of 40.50% with the N 4.0 mmlol/L and S 10 mmol/L. Garlic quality of treatment with N 20.0 mmol/L and S 4.0 mmol/L was optimal, and the membership function value was 0.81, while the control group was the lowest. The results of comprehensive analysis showed that nitrogen and sulfur fertilization significantly influenced quality of garlic bulbs, N 20.0 mmol/L and S 4.0 mmol/L was optimal to improve garlic quality, and there was a significant interaction between nitrogen and sulfur element. The study would be helpful in providing practical theory guidance for fertilization on garlic. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.