Suitable nitrogen fertilization rate effectively improve the quality of summer green tea

Objectives Excessive application of N fertilizer occurs in 30% of the tea plantation area in China, decreasing tea production efficiency and quality. Therefore, we studied the effect of different N application rates on the sensory quality of green tea.

Methods The long-term N fertilization experiment of green tea in Hangzhou, Zhejiang Province, started in 2005. The N application treatments included 0, 119, 285, 474, 569, and 712 kg/hm². Samples of young tea shoots were collected in summer for sensory quality assessment according to the standardized procedure GB/T 23776—2018. Also, the total contents of amino acids, polyphenols, N, and aroma compounds were measured.

Results N application rate affected aroma but not the appearance, taste, colour, and infusion of leaves (P < 0.05). The total amino acids increased with the increase in N application rate, reaching the peak at N 474 kg/hm² and decreased at N 569 kg/hm² and N 712 kg/hm². The total polyphenol content increased with the increasing of N application rate and reached the highest polyphenols vs. amino acids ratio at N 712 kg/hm². However, the total N content in the green tea at N 569 kg/hm² and N 712 kg/hm² was lower than that at N 474 kg/hm². Amino acids content was the highest at N 285 kg/hm² and N 474 kg/hm², including theanine, glutamine, and aspartic acid, which were all closely related to the umami taste. From N 0–285 kg/hm², the R-OH compounds such as β-linalool, nerolidol, and ketones increased while alkene contents decreased. There were no obvious regular changes in the aroma related aldehydes, ester compounds, and other compounds.

Conclusions Nitrogen fertilization at 285–474 kg/hm² is beneficial for forming good tea quality due to the high contents of umami related amino acids and dominant aroma compounds.