A region-specific soil health assessment protocol and evaluation for Sub-Saharan Africa

Abstract

Tropical croplands sit on strongly weathered soils where soil functions and ecosystem services such as carbon storage are constrained by texture, mineralogy, climate, and pedogenesis, making direct comparison with temperate-derived soil health benchmarks unreliable. Here we develop a region-specific soil health assessment protocol and evaluation for Sub-Saharan Africa that benchmarks soil health indicators (e.g., organic carbon) against their ecological context rather than fixed concentration thresholds. We used soil organic carbon to illustrate the tool application. Using 28,000 georeferenced topsoil samples from Ethiopia, we combine soil, climate, vegetation, and terrain covariates in a hierarchical Bayesian model that estimates context-specific soil organic carbon distributions and uncertainty. The framework converts measured soil health indicators (organic carbon) into percentile scores and opportunity gaps, quantifying how far a soil sits from the upper range of similar soils under comparable climate. Results show that soil texture, mineralogy, and temperature primarily set the attainable soil organic carbon ceiling; management determines how closely individual fields approach it. The framework provides field-scale targets for realistic soil health gains across tropical agricultural landscapes. A soil health assessment protocol and evaluation framework for Sub-Saharan Africa was developed, using soil organic carbon to illustrate its application, setting context-aware, percentile-based benchmarks to assess soil health using 28,000 georeferenced samples.