Agricultural practices drive elevated rates of topsoil decline across Kenya, but terracing and reduced tillage can reverse this

Feeney, Christopher J. ORCID: https://orcid.org/0000-0003-2175-1842; Robinson, David A. ORCID: https://orcid.org/0000-0001-7290-4867; Thomas, Amy R.C. ORCID: https://orcid.org/0000-0002-4929-7285; Borrelli, Pasquale ORCID: https://orcid.org/0000-0002-4767-5115; Cooper, David M. ORCID: https://orcid.org/0000-0001-7578-7918; May, Linda ORCID: https://orcid.org/0000-0003-3385-9973. 2023 Agricultural practices drive elevated rates of topsoil decline across Kenya, but terracing and reduced tillage can reverse this. Science of the Total Environment, 870, 161925. 13, pp. https://doi.org/10.1016/j.scitotenv.2023.161925

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Abstract/Summary

As agricultural land area increases to feed an expanding global population, soil erosion will likely accelerate, generating unsustainable losses of soil and nutrients. This is critical for Kenya where cropland expansion and nutrient loading from runoff and erosion is contributing to eutrophication of freshwater ecosystems and desertification. We used the Revised Universal Soil Loss Equation (RUSLE) to predict soil erosion rates under present land cover and potential natural vegetation nationally across Kenya. Simulating natural vegetation conditions allows the degree to which erosion rates are elevated under current land use practices to be determined. This methodology exploits new digital soil maps and two vegetation cover maps to model topsoil (top 20 cm) erosion rates, lifespans (the mass of topsoil divided by erosion rate), and lateral nutrient fluxes (nutrient concentration times erosion rate) under both scenarios. We estimated the mean soil erosion rate under current land cover at ~5.5 t ha−1 yr−1, ~3 times the rate estimated for natural vegetation cover (~1.8 t ha−1 yr−1), and equivalent to ~320 Mt yr−1 of topsoil lost nationwide. Under present erosion rates, ~8.8 Mt, ~315 Kt, and ~ 110 Kt of soil organic carbon, nitrogen and phosphorous are lost from soil every year, respectively. Further, 5.3 % of topsoils (~3.1 Mha), including at >25 % of croplands, have short lifespans (<100 years). Additional scenarios were tested that assume combinations of terracing and reduced tillage practices were adopted on croplands to mitigate erosion. Establishing bench terraces with zoned tillage could reduce soil losses by ≥75 %; up to 87.1 t ha−1 yr−1. These reductions are comparable to converting croplands to natural vegetation, demonstrating most agricultural soils can be conserved successfully. Extensive long-term monitoring of croplands with terraces and reduced tillage established is required to verify the efficacy of these agricultural support practices as indicated by our modelling.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1016/j.scitotenv.2023.161925
UKCEH and CEH Sections/Science Areas:	Soils and Land Use (Science Area 2017-) Water Resources (Science Area 2017-)
ISSN:	0048-9697
Additional Information. Not used in RCUK Gateway to Research.:	Open Access paper - full text available via Official URL link.
Additional Keywords:	soil erosion, topsoil lifespan, lateral nutrient flux, potential natural vegetation, agricultural support practices, modelling
NORA Subject Terms:	Earth Sciences Ecology and Environment
Date made live:	16 Feb 2023 15:07 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/533975

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