Fertility Assessment and Risk Management in Tea Plantations: Role of P-Promoted Metals’ Availability

Nitrogen (N), phosphorus (P), and potassium (K) are important fertilizers frequently applied to soils to ensure agricultural production. However, how an excess of N, P and K affects metals’ geochemical availability, and thereby soil fertility, is poorly under-stood in the tea agro-system. Instead of using the total concentration, this study evaluated soil fertility based on the available concentration of fertilizers (N, P, and K), macro elements (Ca, Mg, Fe, and Mn), and trace elements (Cu and Zn) on tea plantations in the eight main tea-producing regions of Puerh, Yunnan Province, Southwest China. In addition, the correlations of fertilizer, soil pH, and metals’ availability, as well as their effect on soil fertility, were clarified. The results showed that tea-growing soils were acidified (pH = 3.83–5.5; n = 323). Soil pH (98.7%), available Fe (100%), Ca (98.5%), Cu (97.2%), and Zn (86.4%) were within suitable ranges for tea tree growth, while N (97%), Mg (84%), and P (86.1%) should be enhanced. The overall fertility (IFI = 0.47–0.89) was distributed in levels I–III, with Jiangcheng showing the highest IFI at level I. This was attributed to the highly available concentration of metals induced by low pH (3.83–4.99). In terms of the driven factor, available P and K posed greater effects than available N in mediating the availability of metals (R = 0.14–0.28 and 0.27–0.75; p < 0.01 or p < 0.05) by decreasing soil pH (R = −0.17 and −0.17; p < 0.01) in the studied tea plantations. This study indicates that more attention should be paid to P and K during fertilization management for tea plantations.