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” (AfDE). In comparisons between AfDE and adjacent soils (AS), AfDE 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, AfDE 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 AfDE make a disproportionately large contribution (24%) to total farm household income despite its limited spatial extent. Radiocarbon (14C) aging of PyC indicates the recent development of these soils (115–692 years before present). AfDE 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.