Soil acidification associated with changes in inorganic forms of N reduces the yield of tea (Camellia sinensis)

In this study, 145 tea soils were analyzed and exploredthe relationship between soil pH and soil nitrogen forms and tea yield, which is helpful for more accurate fertilization management, so as to improve tea yield and restore acidified soil. The results showed that 82.1% of the soil samples had a pH < 4.50. Tea yield was positively and significantly (p < 0.01) correlated with soil pH. The dominant N form in tea soils was N(NO3−) in pH 3.00–4.00 and was N(NH4+) in pH 4.50–5.50. With the pH gradient of 3.50–4.50, tea yield was positively significantly (p < 0.01) correlated with soil N(NH4+) content, and was negatively significantly (p < 0.01) correlated with soil N(NO3−) content. These results revealed that soil pH is the determinant factor for soil N forms and tea yield. Soil acidification reduced soil N(NH4+) supply, resulting in the decline of tea yield. We suggested that increasing the soil pH cooperated with input of N(NH4+) fertilizer is primary and foremost for soil pH < 4.5. Increasing N(NH4+) fertilizer thus regulates the ratio of N(NO3–)/N(NH4+) to 1:1 or less is a practical proposal for the soil pH gradient of 4.5–5.5.