Improving yield and quality of autumn tea with drip irrigation under appropriate nitrogen and potassium fertilization

Abstract: China is a country with the highest tea production and planting area in the world, but the average yield per unit area is low and the production scale of high-quality tea develops very slowly. Unreasonable fertilization is one of the key factors restricting the improvement of yield and quality of tea. Field experiment was conducted to study the effect of different nitrogen (pure N) fertilization levels (0 kg/hm2, N0; 45 kg/hm2, N1; 75 kg/hm2, N2; 105 kg/hm2, N3) and potassium (K2O) fertilization levels (0 kg/hm2, K0; 27 kg/hm2, K1; 54 kg/hm2, K2; 81 kg/hm2, K3) on autumn tea yield and quality under drip irrigation in Rizhao, Shandong Province from May to October in 2018. The results showed that the yield of autumn tea increased with the increase of nitrogen fertilization in the range of 0-75 kg/hm2, then reached the maximum value in the range of 75-105 kg/hm2 (N3K2 and N2K2). Nitrogen fertilization could significantly increase the content of chlorophyll a and total chlorophyll but had no significant effect on chlorophyll b, the chlorophyll content was the highest at a nitrogen fertilization rate of 105 kg/hm2 (N3K2). The content of amino acid, caffeine and water extract of each nitrogen treatment increased with the increase of nitrogen fertilization rate, and the maximum value was obtained at the nitrogen fertilization rate of 105 kg/hm2 (N3K2). The ratio of phenol to amino acid was applied to nitrogen reached a minimum value of 10.97 at the nitrogen fertilization of 105 kg/hm2 (N3K2) which was significantly lower than other treatments. The maximum content of tea polyphenols was obtained at the nitrogen fertilization amount of 75 kg/hm2 (N2K2). The yield of autumn tea increased with the increase of potassium fertilization and reached the maximum yield of 1 711.37 kg/hm2 (N2K3) when the potassium fertilization amount was 81 kg/hm2, which was 23.58% higher than that the treatment without potassium fertilization. All the treatments with potassium fertilization had a significantly higher yield of autumn tea than the N2K0 treatment, however, there was no significant difference between the potassium fertilization treatments. Potassium fertilization promoted the content of chlorophyll a, chlorophyll b and total chlorophyll, and when potassium fertilization rate was 81 kg/hm2 (N2K3), chlorophyll content was the highest. The content of caffeine reached the maximum at the potassium fertilization rate of 81 kg/hm2 (N2K3). The content of amino acids, tea polyphenol, and water extracts respectively reached a maximum at the potassium fertilization amount of 54 kg/hm2 (N2K2). The ratio of phenol to amino acid reached a minimum value kg/hm2 of 11.49 when potassium was applied at 27 kg/hm2 (N2K1). Comprehensively thinking of yield and quality of all fertilization treatments, the highest autumn tea yield (N2K2, N3K2 and N2K3) and chlorophyll content (N3K2 and N2K3) were obtained at the nitrogen fertilization rate of 75-105 kg/hm2 and potassium fertilization rate of 54-81 kg/hm2, while the nitrogen fertilization rate of 105 kg/hm2 and potassium fertilization rate of 54 kg/hm2 (N3K2) obtained the maximum content of caffeine and minimum ratio of phenol to amino acid. All treatments had no significant effect on the content of autumn tea water extracts. Therefore, the nitrogen fertilization amount of 105 kg/hm2 and potassium fertilization amount of 54 kg/hm2 (N3K2) had the most significant promoting effect on the yield and quality of autumn tea and was recommended as an optimal combination for fertilization management.