Biostimulants and Microbial Technologies for Sustainable Field Crops: From Mechanisms to Precision Deployment

Biological inputs often perform well in controlled studies yet respond inconsistently in farmers’ fields. This review examines the conditions under which microbial inoculants and non-microbial biostimulants can be deployed as reliable technologies for cereals, grain legumes, oilseeds, fibre, sugar and forage crops. Across 1,087 paired observations from 180 open-field studies, non-microbial biostimulants increased yield by 17.9% on average (95% confidence interval: 16.7-19.0%), but this mean masked variation among products, crops, soils, climates and application strategies. Rhizobia, beneficial bacteria, arbuscular mycorrhizal fungi, Trichoderma, endophytes and designed consortia can improve nitrogen fixation, nutrient mobilisation, root development, stress signalling and rhizosphere function; humic substances, seaweed extracts and protein hydrolysates can strengthen plant acclimation and microbial establishment. We propose a five-fit framework in which reliable field performance depends on crop genotype, soil and resident microbiome, climate and stress timing, formulation and delivery, and management and economics. Biological inputs should therefore be developed and recommended as precision technologies, not universal products. Future progress will depend on identifying effective microbes, developing stable and seed-compatible formulations, tracking their field performance, and predicting response, risk and economic return. The main challenge is no longer finding promising traits, but turning them into reliable, profitable outcomes with proven environmental benefits under real farming conditions.