Next-Generation Agricultural Soil Science: From Rhizosphere Ecology and Soil Microbiomes to Climate-Resilient Farming

Low-input agriculture depends not only on reducing fertiliser use but on improving the capacity of crops to acquire nutrients already present in soil. This critical narrative review evaluates microbial nutrient mining in the rhizosphere as an operational concept encompassing microbial processes that mobilise, mineralise, weather, redistribute or recycle sparingly available native and legacy nutrient pools. The evidence shows that the strongest mechanistic basis exists for phosphorus mobilisation through organic-acid-mediated dissolution, phosphatase-driven mineralisation, microbial turnover and mycorrhizal transport. Potassium release from minerals, iron acquisition through ligand-mediated chemistry, zinc solubilisation and microbial sulfur transformations extend the concept beyond phosphorus, although their agronomic evidence bases are less mature. Root exudates are central because they supply carbon, alter pH and ligand chemistry, and select microbial partners, but this creates an intrinsic trade-off: the same carbon subsidies that stimulate nutrient acquisition can intensify microbial competition and rhizosphere priming of soil organic matter. Meta-analyses and field syntheses indicate that microbial inoculants and arbuscular mycorrhizal fungi can improve nutrient acquisition and yield, yet effect sizes are strongly context dependent and are generally smaller in field than in controlled experiments. A recurring weakness is the assumption that in vitro solubilisation predicts net nutrient transfer to crops; in soil, released nutrients may be sorbed, reprecipitated, immobilised by microbes or lost before root capture. For low-input systems, the most defensible strategy is therefore not indiscriminate inoculation but ecological management of plant-microbiome-soil interactions, combined with targeted inoculants where colonisation and function are demonstrated. Microbial mining should be treated as a means of increasing access and synchrony rather than creating nutrients. Its long-term value depends on replenishing exported nutrient stocks, protecting soil organic matter and matching mobilisation to crop demand. Future progress requires isotope-resolved field experiments, trait-based microbiome design, spatially explicit measurements and multi-season nutrient budgets that distinguish gross mobilisation from net plant acquisition.