Coupling optimization of water-fertilizer for coordinated development of the environment and growth of Pinus massoniana seedlings

A reasonable water and fertilizer supply is key to coordinating nursery stock quality improvement and environmental pollution reduction. Here, the experiment was carried out based on the combinations of four levels of water content (W), substrate available nitrogen (N), phosphorus (P), and potassium (K). The aim was to explore the combining effects of water and fertilizer on the comprehensive growth of Pinus massoniana seedlings, and to obtain the coupling optimization of water-fertilizer. The results indicate that the comprehensive growth index (CGI) of seedlings followed a linear pattern with P and a downward-opening parabola with W, N, and K. The seedling growth was not significantly affected by adjusting the input of other elements when the substrate P ≤ 32.00 mg/kg·dry substrate. Whereas when P was 128.00 mg/kg·dry substrate, the negative effects caused by low water (W was below 45%) could not be alleviated, even if moderate N and K levels were maintained. W and P had direct and significant positive effects on the growth of seedlings, while N and K had negative effects. The combination of 85–91% (W), 65.95–134.27 (N), 128.00 (P), and 215.87–234.00 mg/kg·dry substrate (K) was beneficial to seedling growth. While W of 91% combined with the N, P, and K of 57.39, 88.40, and 123.08 mg/kg·dry substrate coordinated the environmental development and seedling growth. This research showed that P is the key factor affecting the CGI of P. massoniana seedlings. which provides a reference for rational and precise fertilization during the cultivation of P. massoniana seedlings.