Effects of high nitrogen and low phosphorus medium potassium ratios on the yield and quality of Wuyi Rock tea

【Objective】To investigate the effects of reducing the ratio of phosphorus(P) and potassium(K) based on nitrogen (N) in fertilizers on the yield and quality of Wuyi tea, so as to provide a theoretical basis for producing high quality rock tea and fertilization of better nutrient ratios.【Method】In this study,the experimental garden located in Wuyishan City,and tea cultivar was Shuixian. Three different ratios of NPK(N-P₂O₅-K₂O) fertilizers 15-15-15(CK),18-8-18(T1, treatment was reduced the ratio of P) and 21-8-11(T2,treatment was reduced the ratio of P and K) were used. The bud density,the weight of hundred buds and the percentage of standard tea leaves were measured in spring. Five conventional quality indicators including the contents of water extract,soluble sugars,tea polyphenols,free amino acids and flavonoids were determined. The concentrations of three major secondary metabolites such as theanine,caffeine and ECG(epicatechin gallate) were detected by high performance liquid chromatography. The flavor and aroma associated substances were analyzed through Ultra performance liquid chromatography-quadrupole-time of flight mass spectrometer and gas chromatography mass spectrometer,respectively.【Result】The results showed that the different ratios of fertilizer significantly influenced the percentage of standard tea leaves,but had little effects on the bud density and the weight of hundred buds. T2 either significantly increased the percentage of standard tea leaves(P<0.05, the same below),which were about 1.35 and 1.40 times of CK and T1,respectively,or greatly increased the contents of free amino acids and water extracts in tea,and thus improving the quality of fresh tea leaves. Constrained principal coordinate analysis (CPCoA) of untargeted metabolomics,with fertilization treatments as restrictive condition,showed that the flavor and aroma associated metabolites were significantly influenced by the ratios of N,P,K,whose contributions were about 23.30% and 22.00%,respectively. The liquid phase analysis exhibited that T2 significantly increased the concentrations of the flavonoid compound Hyacinthin,the ether compound Sorafenib,and the main secondary metabolites theanine and caffeine. The gas chromatographic analysis showed that T2 increased the concentrations of aroma related metabolites obviously,including creamy aroma substance 2,3-Octanedione. The results above revealed that T2 could increase the concentration of flavor and aroma metabolites,and thus improving the tea quality,especially aroma.【Conclusion】Optimal fertilizers ratio of N,P,K, namely high N,low P and moderate K,effectively increases yield and improve the quality of Wuyi tea,especially flavor and aroma quality.