Biochemical Transformation of Agricultural Residues into Biostimulants for Climate‑Resilient Agriculture: Mechanistic Insights and Circular Bioeconomy

Valorizing agricultural residues as biostimulants offers a promising strategy for sustainable food production and waste management under climate stress. Globally, over 3.7 billion tonnes of crop residues are generated annually, much of which is burned or underutilized, leading to soil degradation and greenhouse gas emissions. Despite the rapid expansion of biostimulant research, most existing reviews focus on commercial formulations or agronomic outcomes, with limited synthesis linking the biochemical transformation of crop residues to their molecular mechanisms and agroecosystem impacts. This review addresses this gap by integrating biochemical processing pathways, mechanistic insights, and field-based evidence on residue-derived biostimulants, including humic and fulvic extracts, compost teas, protein hydrolysates, biochar-based amendments, and nano-enabled formulations. These bioactive products modulate rhizosphere microbiomes, regulate nutrient transporter activity, enhance nutrient bioavailability, and improve root architecture, thereby strengthening crop tolerance to drought and salinity stress. Field studies report improvements in nutrient-use efficiency, soil organic carbon, antioxidant enzyme activity, and crop yield. Biochar–microbe consortia further enhance carbon sequestration and can reduce emissions associated with residue burning by up to ∼90%, linking residue valorization with measurable climate benefits. Economically, residue-derived biostimulants can reduce dependence on synthetic fertilizers, improve farm profitability, and create opportunities for carbon credit incentives. To support large-scale adoption, this review highlights the need for residue-specific processing protocols, standardized formulation and quality metrics, and integrated life cycle and techno-economic assessments within enabling regulatory and market frameworks. Overall, residue-derived biostimulants represent scalable, low-carbon inputs capable of supporting resilient soils, stable yields, and a circular agri-food bioeconomy.