Mapping and synthesis of evidence on soil fertility management, fertilizer use efficiency, and greenhouse gas outcomes

Soil fertility management influences fertilizer use efficiency (FUE), crop productivity, and greenhouse gas (GHG) outcomes, yet these dimensions are often reported separately. This study mapped and synthesized evidence linking soil fertility management with FUE and GHG outcomes using a structured analytical framework. Specifically, the study (i) assessed the distribution of soil fertility and nutrient management practices, (ii) explored reported FUE responses, (iii) evaluated GHG outcomes, and (iv) examined integration across soil, efficiency, and emission dimensions. A PRISMA-ScR-informed evidence mapping approach was applied to 40 open-access studies comprising field experiments, long-term trials, surveys, modelling studies, reviews, and meta-analyses. Evidence was extracted using a structured matrix and synthesized using a weighted Evidence Index (EI) and Integrated Evidence Score (IES). Integrated soil fertility management accounted for 12 studies, organic amendments for 10, enhanced-efficiency fertilizers and inhibitors for 9, and precision or optimized nutrient management for 9. Reported NUE values ranged from 25% to 70%, with increases of 10–40% for enhanced-efficiency fertilizers, 15–35% for organic amendments and biochar approaches, and 10–25% for precision or optimized nutrient management. Reported N₂O reductions ranged from 10% to 50% across management categories. NUE, N₂O, and soil organic carbon were reported in 70%, 65%, and 50% of studies, respectively. Category-level EI ranged from 1.79 to 2.17, whereas IES ranged from 1.89 to 2.42, reflecting differences between methodological weighting and dimensional coverage. The synthesis provides a structured basis for harmonizing soil fertility, nutrient efficiency, productivity, and GHG indicators in future evidence synthesis and agricultural management research.