Regenerative Soil Management: Restoring Soil Health, Biodiversity and Ecosystem Functions for Sustainable Agriculture

Root exudates are a chemically diverse and highly regulated interface through which plants modify nutrient availability, microbial activity and soil organic matter turnover in the rhizosphere. This critical narrative review evaluates how molecular control of exudation is coupled to phosphorus, nitrogen, iron, zinc and potassium cycling, and assesses how securely these mechanisms can be translated into agronomic practice. Evidence was integrated across molecular genetics, plant physiology, soil biogeochemistry, microbial ecology and agricultural studies. The strongest mechanistic chains occur where specific metabolites, transport processes and nutrient outcomes have been connected by mutants, transporter studies, isotope tracing or soil-based validation. Examples include carboxylate and proton release by phosphorus-starved cluster roots, coumarin-mediated iron mobilisation in dicots, phytosiderophore-mediated metal acquisition in grasses, legume signalling to rhizobia, and biological nitrification inhibition by grass and sorghum root compounds. By contrast, broad claims that higher total exudation necessarily improves nutrient acquisition are poorly supported because exudates are rapidly sorbed, transformed or mineralised, and can intensify microbial immobilisation or soil organic matter priming as well as nutrient release. Exudate composition, flux, timing and spatial deployment are therefore more informative than total carbon release. Major uncertainty arises from hydroponic sampling artefacts, limited in situ metabolite recovery, weak comparability among analytical workflows, and a shortage of field experiments that link exudate traits to nutrient-use efficiency across contrasting soils. Agronomic opportunities are credible but conditional: breeding or managing crops for inducible, nutrient-specific exudation; exploiting interspecific facilitation and biological nitrification inhibition; and matching crop genotypes with responsive microbiomes are more defensible than attempts to maximise exudation indiscriminately. Progress will depend on soil-realistic phenotyping, isotope-enabled causal experiments, spatially resolved metabolomics, and multi-environment field validation that quantifies both nutrient gains and carbon, greenhouse-gas and ecological trade-offs.