Objectives This study aimed to explore the effects of tea-specific fertilizers on tea yield, quality, soil nutrients and enzyme activities in low-phosphorus tea gardens, and to provide a theoretical basis and technical support for the scientific fertilization of tea plants.

Methods Field experiments were conducted over two consecutive years. In 2024, four treatments were established: CK, conventional nitrogen fertilizer with two split topdressings (N rate: 360 kg/hm²); FF, tea-specific fertilizer with two split topdressings (N rate: 300 kg/hm²; N∶P₂O₅∶K₂O = 2.2∶1∶1.5); FFB, tea-specific fertilizer applied as basal fertilizer plus topdressing (same application rate and nutrient ratio as FF); and FFN, FFB supplemented with 4.8 kg/hm² nitrification inhibitor (same rate, timing, and nutrient ratio as FFB). Soil samples were collected continuously over the 9 months following basal fertilizer application in November to determine soil nutrient contents, including nitrate-N and ammonium-N, as well as soil enzyme activities. Spring tea samples were collected to analyze quality-related components, including catechins and free amino acids. In 2025, two additional treatments were established to further verify the effectiveness of the tea-specific fertilizer: YCK, with the same fertilization timing and application rate as CK; and YFS, with the same fertilization timing and application rate as FFB. Soil samples were collected in January, February, May, July, September, and November to determine soil nutrient contents and soil enzyme activities. Spring tea samples were collected to determine quality-related components.

Results In 2024, application of the tea-specific fertilizer with an N∶P₂O₅∶K₂O = 2.2∶1∶1.5 reduced nitrogen input by 17% while maintaining significant yield and quality improvements under low-phosphorus conditions. Despite this reduction, the FF, FFB, and FFN treatments all achieved significant improvements in both yield and quality, with the FFB treatment demonstrating the most superior performance. Compared with CK, FFB significantly increased tea fresh leaf yield in spring by 101.1%, while total N, P, and K contents in fresh leaves increased by 13.1%, 16.7%, and 18.9%, respectively. In terms of quality, tea polyphenol content did not change significantly, whereas free amino acid content increased significantly by 21.5%. Notably, L-theanine content increased by 1.6-fold, and the tea polyphenol-to-amino acid ratio decreased significantly to 5.6, indicating improved taste quality. In 2025, the effectiveness of the tea-specific fertilizer was further confirmed: compared with YCK, YFS significantly increased spring tea fresh leaf yield by 98.2%. Tea polyphenol content showed no significant change, whereas free amino acid content increased significantly by 33.3%, and the tea polyphenol-to-amino acid ratio decreased significantly to 6.6. In addition, nitrate reductase (NR) and glutamine synthetase (GS) activities in tea leaves were significantly increased. Partial least squares path modeling (PLS-PM) further indicated that soil enzymes and plant enzymes regulated nutrient uptake efficiency and utilization of nitrogen, phosphorus, and potassium by tea plants, thereby improving yield and quality.

Conclusions Application of tea-specific fertilizer significantly improved soil nutrient supply during the critical period of spring shoot sprouting in low phosphorus tea plantations, thereby enhancing both spring tea yield and quality. Under the identical nutrient ratios and fertilization conditions, the most effective fertilization regime was the application of 70% of the total fertilizer as basal dressing in mid-November, and the remaining 30% as topdressing in late February of the following year.