Mechanistic synergy of biochar, phosphate-solubilizing microbes and MgO nanoparticle enhances phosphorus availability, soil fertility, and crop resilience in phosphorus-fixing soils (Oxisols)

Phosphorus (P) fixation in acidic and alkaline soils is a major global constraint to agricultural productivity, leading to inefficient fertilizer use and environmental pollution. Singular amendment strategies often provide limited success. This study investigates the potential of an integrated soil amendment comprising biochar, phosphate-solubilizing microbes (PSMs), and magnesium oxide nanoparticles (MgO-NPs) to mitigate P fixation and enhance crop performance. A greenhouse pot experiment was conducted using a P-fixing acidic soil (Oxisol). The experimental design included seven treatments: (1) Control; (2) Recommended NPK (R-NPK), (3) Biochar (B), (4) PSMs (M), (5) MgO-NPs (N), (6) Biochar + PSMs (BM), and (7) Biochar + PSMs + MgO-NPs (BMN). The growth, yield, and P uptake of maize (Zea mays L.) were monitored. Soil samples were analyzed for pH, available P, microbial biomass carbon (MBC), and enzyme activities (acid phosphatase, dehydrogenase). The integrated BMN treatment outperformed all others. It significantly increased soil available P by 128% and 65% compared to the Control and R-NPK treatments, respectively. This was concomitant with a shift in soil pH towards neutrality, a 90% increase in acid phosphatase activity, and a 110% increase in MBC over the Control. Plant parameters mirrored these soil improvements: the BMN treatment resulted in the highest plant biomass (125% increase over Control), grain yield (98% increase over Control), and P uptake (155% increase over Control). The BM combination showed intermediate results, while individual amendments had modest, non-significant effects on most parameters. The integration of biochar, PSMs, and MgO-NPs creates a synergistic system that effectively disrupts P fixation. It is concluded that biochar provides a stable habitat for microbes, MgO-NPs directly react with fixed P pools, and PSMs enzymatically mobilize P.