Determining the Necessity of Applying N and P Fertilizer in a Mature Subtropical Torreya Grandis Orchard

Background: In managed orchards, fertilizer treatments facilitate both high productivity and environmental pollution. Because economic profit takes priority over environmental cost, increasing amounts of chemical nitrogen and phosphorus fertilizer have been used in mature subtropical Torreya grandis orchards. However, given the magnitude of global nitrogen deposition, it’s worth considering whether heavy fertilizer treatment is necessary. Methods: To elucidate the balance between T. grandis nutrient demands and the fertilizer supply, we determined the C, N, and P foliar and soil concentrations ([C], [N], [P]) at five orchards undergoing long-term varied intensity fertilizer treatments. Results: After documenting the dynamic variation of available plant nutrients and the corresponding resorption efficiency, we found that increasing the fertilizer supply elevated foliar [P], yet foliar [C] and [N] remained stable. Because T. grandis was already equipped with a high nutrient content, the increased foliar [P] levels decreased C:P and N:P ratios. These results demonstrate that extra fertilizer in the N-saturated environment disturbs P-limitation. Furthermore, we also found that fertilizer supply failed to improve carbon accumulation, which in addition to soil nutrient content and leaf [P], highly impacted productivity. Conclusions: Thus, based on the results of this study, there are ample reasons to propose rejecting N addition in the present orchards, and we recommend organic management as a more conducive method to realize sustainable development.