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Biochemical proxies indicate differences in soil C cycling induced by long-term tillage and residue management in a tropical agroecosystem

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Abstract

Background & aim

A potential benefit of conservation agriculture (CA) is soil organic carbon (SOC) accrual, yet recent studies indicate limited or no impact of CA on total SOC in tropical agroecosystems. We evaluated biochemical indicators of soil C cycling after 9 years (18 seasons) of contrasting tillage with and without maize residue retention in western Kenya.

Methods

Potential activities of C-cycling enzymes (β-glucosidase, GLU; β-galactosidase, GAL; glucosaminidase, GLM; cellobiohydrolase, CEL), permanganate-oxidizable C (POXC), and soil organic matter (SOM) composition (by infrared spectroscopy) were measured.

Results

POXC tended to be greater under reduced tillage and residue retention, but did not significantly differ among treatments (≤ 2% of SOC). Despite no significant differences in SOC concentrations or stocks, activities of all 4 C-cycling enzymes responded strongly to tillage, and to a lesser extent to residue management. Activities of GLU, GAL, and GLM were greatest under the combination of reduced tillage and residue retention relative to other treatments. Reduced tillage produced an enrichment in carboxyl C = O (+6%) and decreased polysaccharide C-O (−3.5%) relative to conventional tillage irrespective of residue management.

Conclusions

Though enzyme activities and POXC are typically associated with SOC accrual, changes in soil C cycling at this site have not translated into significant differences in SOC after 9 years. Elevated enzyme activities may have offset potential SOC accumulation under CA. However, the ratio of C-cycling enzyme activities to SOC was higher under reduced tillage and residue retention relative to other treatments, indicating that stoichiometric scaling of SOC and enzyme activities does not explain absence of significant differences in SOC among tillage and residue managements. Potential factors that may explain the low SOC accrual rates in this tropical agroecosystem included the low, albeit realistic, levels of residue retention, nutrient limitations, and high temperatures favoring decomposition.

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Acknowledgements

We thank CIAT, and specifically John Mukalama and Evonne Oyugi, for providing field and technical support. We are grateful for the support provided by CGIAR Research Program on Water, Land and Ecosystems (WLE). We thank Jordon Wade (The Ohio State University) for performing a pre-submission review of this work. This research was funded a US Borlaug Graduate Student Fellowship Global Food Security and a Henry A. Jastro Award provided by the Soils and Biogeochemistry Graduate Group at University of California-Davis.

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Correspondence to Andrew J. Margenot.

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Responsible Editor: Liz Shaw.

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Margenot, A.J., Pulleman, M.M., Sommer, R. et al. Biochemical proxies indicate differences in soil C cycling induced by long-term tillage and residue management in a tropical agroecosystem. Plant Soil 420, 315–329 (2017). https://doi.org/10.1007/s11104-017-3401-z

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  • DOI: https://doi.org/10.1007/s11104-017-3401-z

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