Significant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan Acrisols

Vegard Martinsen; Jose Luis Munera-Echeverri; Alfred Obia; Gerard Cornelissen; Jan Mulder

doi:10.1016/j.scitotenv.2018.12.452

Significant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan Acrisols

Sci Total Environ. 2019 Apr 10:660:97-104. doi: 10.1016/j.scitotenv.2018.12.452. Epub 2019 Jan 4.

Authors

Vegard Martinsen¹, Jose Luis Munera-Echeverri², Alfred Obia³, Gerard Cornelissen⁴, Jan Mulder²

Affiliations

¹ Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway. Electronic address: vegard.martinsen@nmbu.no.
² Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway.
³ Norwegian Geotechnical Institute (NGI), P.O. Box 3930, Ullevål Stadion, 0806 Oslo, Norway; Department of Agronomy, Faculty of Agriculture and Environment, Gulu University, P.O. Box 166, Gulu, Uganda.
⁴ Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway; Norwegian Geotechnical Institute (NGI), P.O. Box 3930, Ullevål Stadion, 0806 Oslo, Norway.

PMID: 30639722
DOI: 10.1016/j.scitotenv.2018.12.452

Abstract

Conservation farming (CF) involving minimum tillage, mulching and crop rotation may offer climate change adaptation and mitigation benefits. However, reported effects of CF, as applied by smallholders, on storage of soil organic carbon (SOC) and soil fertility in Sub-Saharan Africa differ considerably between studies. This is partly due to differences in management practice, soil type and adoption level between individual farmers. Where CF involves planting basins, year-to-year changes in position of basins make SOC stock estimates more uncertain. Here we assess the difference in SOC build-up and soil quality between inside planting basins (receiving inputs of lime and fertilizer; basins opened each year) and outside planting basins (no soil disturbance or inputs other than residues) under hand-hoe tilled CF in an Acrisol at Mkushi, Zambia. Seven years of strict CF husbandry significantly improved soil quality inside planting basins as compared with outside basins. Significant effects were found for SOC concentration (0.74 ± 0.06% vs. 0.57 ± 0.08%), SOC stock (20.1 ± 2.0 vs. 16.4 ± 2.6 t ha^-1, 0-20 cm), soil pH (6.3 ± 0.2 vs. 4.95± 0.4) and cation exchange capacity (3.8 ± 0.7 vs. 1.6 ± 0.4 cmol_c kg^-1). As planting basins only occupy 9.3% of the field, the absolute rate of increase in SOC, compared with outside basins, was 0.05 t C ha^-1 yr^-1_. This corresponds to an overall relative increase of 2.95‰ SOC yr^-1 in the upper 20 cm of the soil. Also, hot water extractable carbon (HWEC), a proxy for labile organic matter, and potential nitrification rates were consistently greater inside than outside basins. The significant increase in quantity and quality of SOC may be due to increased inputs of roots, due to favorable conditions for plant growth through input of fertilizer and lime, along with increased rainwater infiltration in the basins.

Keywords: CEC; Hand-hoe tillage; Phosphorus; Planting basin; Soil fertility; Soil sampling.