Slightly higher nitrous oxide emissions do not offset the climate benefit of additional SOC storage in two long-term conservation agriculture experiments in sub-humid Zimbabwe

Cardinael Rémi, Shumba Armwell, Thierfelder Christian, Corbeels Marc, Six Johan, Chikowo Régis. 2024. Slightly higher nitrous oxide emissions do not offset the climate benefit of additional SOC storage in two long-term conservation agriculture experiments in sub-humid Zimbabwe. . UM6P, Chair of Soil Sciences, AITTC. Ben Guerir : UM6P, Résumé, 2 p. International Symposium on Soil Organic Matter (SOM2024). 9, Ben Guerir, Maroc, 26 Mai 2024/31 Mai 2024.

Résumé : Soils store significant amounts of carbon (C) and play a critical role in mitigating climate change through C sequestration. This study evaluated the potential contribution of each conservation agriculture (CA) principle or their different combinations to soil C stock and greenhouse gas emissions. A CA component emission experiment was established in 2013 in Zimbabwe on an abruptic Lixisol (DTC site) and a xanthic Ferralsol (UZF site). The main crop was maize (Zea mays L.) and treatments with rotation included cowpea (Vigna unguiculate L. Walp.). Gas samples were regularly collected using the static chamber method in the maize rows and inter-rows during the 2019/20 and 2020/21 seasons. In 2021, soil samples for SOC were taken down to 1 m soil depth and SOC stocks were calculated using the equivalent soil mass approach. In the 2019/20 cropping season, cumulative N2O-N emissions were significantly higher in mulch and cowpea rotation treatments at DTC and UZF, respectively and ranged from 215 to 496 g and 226 to 395 g N2O-N ha−1 yr−1. There were no significant differences in yield-scaled N2O emissions between treatments at both sites for the two seasons. Cumulative CO2-C efflux was not significantly different between treatments, but it was significantly higher in the rows than in the inter-rows. SOC stocks under no tillage (NT) treatments at the two sites were not significantly different, and even slightly lower, than under conventional tillage (CT). Significantly higher cumulative SOC stocks were found within the top 20 cm at DTC and UZF in the no-tillage with mulch (NTM) treatment compared to NT and CT. SOC accumulation rate was highest in NTM (0.30 and 0.26 Mg C ha-1 year-1 at DTC and UZF, respectively) compared to CT. Overall, the study showed generally low greenhouse gas emissions, and increased N2O emissions in the mulch and rotation treatments could not offset the climate benefit due to additional SOC storage. It also showed that no tillage alone cannot lead to additional SOC storage in these degraded soils in the sub-humid tropics, and that the combination of the three CA principles is required it increase SOC stocks.

Mots-clés libres : Soil organic carbon, Climate change mitigation, Conservation agriculture, Nitrous oxide emissions, Deep soil organic carbon stocks

Auteurs et affiliations

• Cardinael Rémi, CIRAD-PERSYST-UPR AIDA (ZWE) ORCID: 0000-0002-9924-3269
• Shumba Armwell, University of Zimbabwe (ZWE)
• Thierfelder Christian, CIMMYT (ZWE)
• Corbeels Marc, CIRAD-PERSYST-UPR AIDA (KEN)
• Six Johan, ETH (CHE)
• Chikowo Régis, University of Zimbabwe (ZWE)

Source : Cirad-Agritrop (https://agritrop.cirad.fr/609496/)

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