Biochar (a carbon-rich product from the pyrolysis of organic materials) addition to agricultural soils has been proposed as a novel technology for enhancing soil C storage and fertility, but few studies have evaluated effects on nutrients using an integrated perspective. Previous studies have demonstrated that biochar has the potential to improve bioavailable phosphorus (P) in organic farming systems on sandy soils; yet the underlying mechanisms are poorly understood. We hypothesized that the unique characteristics of wood biochar could induce changes in soil microbial communities, which subsequently provide biotic controls on soil P availability through solubilization and/or mineralization and that these shifts would be reflected in microbial P gene expression. To test this hypothesis, we measured the abundance and diversity of bacterial and fungal communities in sandy soils of organically-managed farmlands that had been amended with locally produced wood biochar, and analyzed the relationship of these communities to shifts in biologically based P (i.e. soluble P extracted by CaCl2, chelate extractable P, enzyme extractable organic P, and mineral occluded P), genes encoding for the synthesis of phosphatase (mineralization), and genes encoding for the production of small molecular weight organic acids (solubilization).
Results/Conclusions
Three months after the application of wood biochar to sandy soils resulted in a significant elevation in P bioavailability (particularly chelate extractable P and enzyme extractable P) and a noted shift towards a bacterial dominated microbial community. However, contrary to our hypothesis, the abundance of genes dictating soil phosphatase synthesis or organic acid production were unaltered by biochar amendments. Biologically based P was neutrally to negatively correlated with genes dictating P mobilization, while positively correlated with soil bacterial to fungal ratio. Hence, we suggest that the shift in P bioavailability could be controlled by abiotic mechanisms such as biochar-induced stabilization of soil organic matter and adsorption/desorption of P associated with organo-mineral complexes. Although there was no specific molecular evidence of soil microorganism-mediated P mobilization, locally produced wood biochar increased soil P bioavailability which could benefit agricultural soil health management and ecosystem service delivery in organic farming systems.