Global evidence map links soil fertility management to fertilizer efficiency and greenhouse gas outcomes

A sweeping synthesis of 40 open-access studies has mapped how the world’s soil fertility research connects three domains that scientists too often study in isolation: how farmers manage soil fertility, how efficiently crops use applied fertilizer, and what happens to greenhouse gas emissions. The review, published in Discover Soil, applied a PRISMA-ScR-informed evidence mapping approach to field experiments, long-term trials, surveys, modelling studies, reviews and meta-analyses published between 2010 and 2026. Its central finding is striking: the literature rarely measures all three dimensions together, leaving a fragmented picture of whether practices that boost fertilizer efficiency also cut emissions of nitrous oxide, a greenhouse gas nearly 298 times more potent than carbon dioxide over a century.

The evidence base fell into four broad management categories. Integrated soil fertility management accounted for 12 of the 40 studies, organic amendments including biochar, compost and manure for 10, enhanced-efficiency fertilizers and inhibitors for 9, and precision or optimized nutrient management for another 9. Reported nitrogen use efficiency values across the evidence ranged from roughly 25 percent to 70 percent, a reminder that global nitrogen budgets indicate only about 30 to 50 percent of applied nitrogen is typically recovered by crops, with the remainder lost through volatilization, leaching and denitrification. Those losses are tightly linked to nitrous oxide emissions, the review’s most frequently reported greenhouse gas indicator, appearing in about 65 percent of studies.

Within those ranges, the mapped studies reported meaningful gains from specific practices. Enhanced-efficiency fertilizers were associated with nitrogen use efficiency increases of approximately 10 to 40 percent, biochar and organic amendment approaches with increases of 15 to 35 percent, and precision or optimized nutrient management with gains of roughly 10 to 25 percent. On the emissions side, reported nitrous oxide reductions spanned 10 to 50 percent across the management categories, depending heavily on the practice and experimental context. The authors stress that these are ranges reported by the included studies, not pooled meta-analytic estimates, because the underlying research differed in crops, soils, climates, fertilizer rates and outcome calculations.

Several included studies illustrate the scale of these effects. A global meta-analysis by Huo and colleagues, synthesizing 256 studies and 2,109 observations, reported nitrogen use efficiency increases of 26.9 percent for rice, 10.8 percent for maize and 11.1 percent for wheat under subsurface fertilizer application compared with broadcast application. Puga and colleagues found that two biochar-based nitrogen fertilizers produced average maize yields 26 percent higher than urea, with one formulation raising nitrogen use efficiency by 12 percent. Liu and colleagues reported agronomic efficiency gains of 7.3 to 26.8 percent for efficiency-enhanced fertilizers relative to common urea, while Wang and colleagues documented fertilizer nitrogen recovery efficiency increases of 16.9 to 44.8 percent following optimized application and the use of nitrogen synergists.

The emissions evidence is equally detailed but more context-dependent. Akiyama and colleagues synthesized 113 datasets from 35 field studies evaluating nitrification inhibitors, polymer-coated fertilizers and urease inhibitors as mitigation options. Ren and colleagues showed that combining urea ammonium nitrate with the inhibitors DCD and NBPT reduced both nitrous oxide and ammonia emissions while improving nitrogen use efficiency in summer maize. Yet the biochar literature reveals why no single direction of response can be assumed: Wei and colleagues found that biochar reduced nitrous oxide emissions at lower nitrogen rates but that responses differed with nitrogen rate and cropping season, while Lu and colleagues reported that biochar reduced nitrous oxide and greenhouse gas intensity while actually increasing global warming potential relative to the control.

One of the review’s most consequential findings concerns indicator fragmentation. Nitrogen use efficiency was reported in about 70 percent of the studies, nitrous oxide in about 65 percent, and soil organic carbon in about 50 percent, but agronomic efficiency, partial factor productivity and global warming potential appeared far less often. Studies variably employ recovery efficiency, partial factor productivity, emission intensity and global warming potential, often without standardized definitions. The authors argue that this heterogeneity constrains reproducibility and prevents researchers from mapping relationships between management practices, efficiency outcomes and emission pathways within a unified analytical structure.

To quantify this fragmentation, the team developed a Practice-Efficiency-Emission matrix and two composite measures. The Evidence Index characterized the methodological profile of each management category, weighting field experiments at 2.0, integrated field and laboratory studies at 2.5, multi-site and meta-analytical studies at 3.0, and modelled or survey-based estimates at 1.5. The Integrated Evidence Score instead measured how many of the three evidence dimensions—soil fertility, fertilizer use efficiency and greenhouse gas emissions—each category addressed. The two measures told different stories: precision and optimized nutrient management scored highest on methodology at 2.17, while integrated soil fertility management scored highest on dimensional coverage at 2.42, with Enhanced-efficiency fertilizers lowest on integration at 1.89.

That divergence between methodological strength and dimensional integration is itself a key insight. Studies with high methodological weighting did not necessarily address all three evidence dimensions, while several studies with broad coverage were reviews or syntheses with lower methodological weights. The extraction matrix also revealed uneven geographic reporting: five records had global or multi-region scope, specific locations were reported for India, China, Bangladesh and Afghanistan, four records were identified as tropical settings without a stated country, and for 26 of the 40 records the geographic scope was not stated at all. The authors note this incomplete reporting limits direct comparison across soil, climate, crop and management contexts.

Global disparities in fertilizer access sharpen the stakes. High-input systems in North America, Europe and East Asia are often characterized by nitrogen surpluses and elevated emission risks, while many systems in Sub-Saharan Africa operate under nutrient-limited conditions with low input use and constrained productivity. Farm-level analyses included in the synthesis, such as a Bangladeshi wheat survey estimating a mean nitrogen use efficiency of 37.4 percent, show that socioeconomic factors, input accessibility and management decisions strongly influence efficiency outcomes and emission profiles. In low-input contexts, integrated approaches have raised yields and improved soil fertility, but empirical evidence linking those improvements to measurable emission reductions remains limited.

The synthesis ultimately argues for treating nutrient management as a soil-plant-environment system rather than a search for a single best practice. Fertilizer rate, nutrient source, formulation, placement, organic amendments, soil fertility status and water management jointly determine whether nitrogen is retained, recovered or lost as greenhouse gases. The authors call for future studies to report soil properties, nutrient inputs, nutrient recovery, crop productivity and greenhouse gas outcomes within the same experimental framework, with harmonized efficiency terminology and explicit system boundaries distinguishing absolute emissions from emission intensity. Such harmonization, they conclude, would provide the structured basis needed to translate localized findings into scalable, context-specific mitigation strategies for agricultural systems worldwide.

Subject of Research: Evidence mapping of soil fertility management practices, fertilizer use efficiency and greenhouse gas outcomes in agricultural systems

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

Article References: Nassary, E. K., Magubika, A. J., Mhagama, E. A., Salimu, A. I., Kilasi, N. L., Tryphone, G. M., & Shitindi, M. J. (2026). Mapping and synthesis of evidence on soil fertility management, fertilizer use efficiency, and greenhouse gas outcomes. Discover Soil, 3(1), Article 193. https://doi.org/10.1007/s44378-026-00354-2

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00354-2

Keywords: soil fertility, fertilizer use efficiency, nitrogen use efficiency, nitrous oxide, greenhouse gas emissions, biochar, integrated soil fertility management, enhanced-efficiency fertilizers, precision agriculture, organic amendments, evidence synthesis, agriculture