Indigenous African soil enrichment as a climate-smart sustainable agriculture alternative

Abstract

We describe for the first time a current indigenous soil management system in West Africa, in which targeted waste deposition transforms highly weathered, nutrient- and carbon- poor tropical soils into enduringly fertile, carbon- rich black soils, hereafter “African Dark Earths” (Af DE ). In comparisons between Af DE and adjacent soils ( AS ), Af DE store 200–300% more organic carbon and contain 2–26 times greater pyrogenic carbon (PyC). PyC persists much longer in soil as compared with other types of organic carbon, making it important for long- term carbon storage and soil fertility. In contrast with the nutrient- poor and strongly acidic ( pH 4.3–5.3) AS , Af DE exhibit slightly acidic ( pH 5.6–6.4) conditions ideal for plant growth, 1.4–3.6 times greater cation exchange capacity, and 1.3–2.2 and 5–270 times more plant- available nitrogen and phosphorus, respectively. Anthropological investigations reveal that Af DE make a disproportionately large contribution (24%) to total farm household income despite its limited spatial extent. Radiocarbon ( 14 C) aging of PyC indicates the recent development of these soils (115–692 years before present). Af DE provide a model for improving the fertility of highly degraded soils in an environmentally and socially appropriate way, in resource- poor and food- insecure regions of the world. The method is also “climate- smart”, as these soils sequester carbon and enhance the climate- change mitigation potential of carbon- poor tropical soils.