Long-term application of silicate fertilizer alters microbe-mediated phosphorus cycling in paddy soils

Rice plants require a large amount of phosphorus (P) fertilizer for cultivation. However, much of the P added to soils is fixed and unusable by rice plants. The use of silicate fertilizers to improve P availability to plants has been documented, but the mechanism remains unclear. We studied soil P pools and microbe-regulated P cycling in rice fields after 30-year application of silicate fertilizer (SF) made from blast-furnace slag. Long-term application of SF did not significantly change available P in the soil, but significantly increased P uptake by rice plants due to higher yield. Under long-term SF fertilization compared to no-SF, the abundance of functional genes for organicP mineralization ( phoA , phoB , and phy ) and inorganic-P solubilization ( ppx , ppk , and gcd ) increased, whereas the genes for P uptake and transport systems ( pst and pit ) and P starvation response ( phoB ) did not change significantly. Increased microbial P mineralization and solubilization was attributed to the increased P demand by the crop. Structural equation modeling shows that microbial P-transforming gene community was associated with Si availability, soil pH, plant P uptake, and soil C:P and N:P stoichiometry. A significant decrease in Fe-P and an increase in Ca-P pools under Si fertilizer addition indicated their respective roles in P availability and P reserve in the SF treatment. We conclude that long-term application of SF increased P uptake by rice plants by enhancing microbial mobilization of soil P and crop yields, potentially improving recycling of slag while reducing the use of chemical P fertilizers that can lessen environmental risks associated with non-point source pollution.