A balanced reduction in mineral fertilizers benefits P reserve and inorganic P-solubilizing bacterial communities under residue input

Given the contribution of crop residue to soil phosphorus (P) pools, reducing mineral fertilizers should be a worthy management goal in agro-ecosystems for the rational use of scarce P resources. However, little data on whether and how P availability and P-solubilizing bacterial communities change under this condition are accessible. Here, in addition to conventional NPK fertilizers (NPK) and maize straw mulching (NPKS), residue mulching combined with a 20% reduction in only mineral P (NPmKS) or simultaneous NPK (mNPKS) was used on fields with successive years of mineral fertilizers in Northeast China. After two growing seasons, maize yield and total P were consistent across treatments. Nonetheless, compared to NPK, easily labile inorganic P and stable organic P significantly increased in NPKS, which suggests that the risk of P loss and P reserve for long-term transformation increased with residue input. The content of the two P forms recovered separately in mNPKS and NPmKS, which indicates that a balanced reduction in mineral fertilizers may be better for maintaining the P supply. High-throughput sequencing of the pqqC gene, which encodes pyrroloquinoline quinone related to P solubilization, suggested significant contrasts between the inorganic P-solubilizing bacterial communities of NPK and other treatments, nearly 70% of which could be explained by P fractions. In particular, moderately labile inorganic P played a bridging role between P fractions and P-solubilizing bacterial species. Moreover, the correlation between P fractions and P-solubilizing bacteria was enhanced when pH increased, i. e. , in mNPKS, which further confirmed the advantages of a balanced reduction in mineral fertilizers in P-solubilizing bacteria.

Automated summary

The study highlights the importance of reducing mineral fertilizers in agricultural ecosystems for the efficient use of phosphorus resources. Residue inputs increase both the risk of phosphorus loss and long-term phosphorus reserves, balancing reductions in mineral fertilizers are more effective in maintaining phosphorus supply.