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

Plant biostimulants and related growth-promoting inputs are increasingly used to improve crop productivity, nutrient use efficiency and stress resilience while reducing dependence on intensive fertilisation. Their agronomic value is difficult to generalise because function-defined biostimulants, nutrient-mobilising microbial inoculants and other growth-promoting inputs differ in composition, mechanism and dependence on crop genotype, soil, climate, nutrient supply and application practice. This critical narrative review evaluates functional boundaries, mechanistic evidence, field performance and integration with crop nutrition. Literature was identified through live scholarly searching and citation tracing, with priority given to verified peer-reviewed studies, field experiments, meta-analyses and mechanistic work. The evidence supports recurring pathways involving root-system architecture, membrane transport and nutrient assimilation, microbial nutrient mobilisation or fixation, phytohormone and redox signalling, and abiotic-stress acclimation. Mechanistic plausibility, however, does not ensure field reliability. Quantitative syntheses generally show positive average responses, but effects are smaller and more variable under field conditions, and crop identity, soil properties, formulation, dose, application method, native microbiota and baseline fertility can materially alter outcomes. Statistically significant mean responses also should not be equated automatically with economically meaningful farm benefits. The strongest case for crop-nutrition integration is therefore context-dependent improvement in nutrient capture, utilisation and yield stability, not universal fertiliser replacement. Reliable translation requires product-resolved characterisation, multi-site and multi-season testing, explicit nutrient-response gradients, clearly defined nutrient use efficiency metrics, and economic assessment alongside biological efficacy. Biostimulants can contribute to nutrient-efficient agronomy when treated as evidence-defined management components rather than interchangeable growth-promoting products.