Supplementary file 1_Nitrogen-centered nutrient innovation for decoupling agricultural productivity from greenhouse-gas intensity: evidence, limits, and implementation pathways.docx

This critical review evaluates nitrogen-centered nutrient innovations through a boundary-explicit, two-axis framework: evidence confidence for a stated productivity-GHG decoupling outcome and implementation readiness in a specified context. The synthesis covers enhanced-efficiency fertilizers (EEFs), biological nitrogen fixation (BNF), biological nitrification inhibition (BNI), site-specific nutrient management (SSNM), 4R stewardship, precision placement, digital decision support, circular nitrogen recovery, and integrated nutrient management (INM).

Direct evidence requires paired crop-output and GHG data; nitrogen-use efficiency, fertilizer savings, nutrient-loss reduction, or soil-quality responses alone are classified as partial or supporting evidence. Evidence confidence is highest for locally calibrated SSNM, 4R rate-timing-placement practices, and selected EEFs in high-surplus or high-loss systems, although performance varies with crop, soil, climate, baseline nitrogen rate, and the measured boundary.