18th Congress of the European Society for Agronomy

The effect of silicate, carbonate, and sulphate calcium amendments on the mineralizability and persistence of soil organic carbon: a comparative study

Not scheduled

15m

Les Dortoirs (1st floor) (The Couvent des Jacobins)

Poster Synergies between short- and long-term goals Poster session #2

Speakers

Ms Mailis Belhocine (Groupe Roullier | Université de Caen Normandie)Mrs Mariana Devault (Groupe Roullier | Cornell University)

Description

Soils account for the largest reservoir of terrestrial organic carbon1. However, soil organic carbon (SOC) losses associated with cropland cultivation are substantial2,3 and expected to increase with global warming4,5. Major implications of SOC losses include the exacerbation of climate change (as CO2 is released to the atmosphere) and the decline of soil health6. To circumvent these losses, the adoption of climate-smart crop practices promoting SOC accrual, such as Enhanced Rock Weathering (ERW, which consists of amending soils with crushed fast-reacting magnesium or calcium-rich silicate rocks, e.g., wollastonite) are key7. By capturing and converting CO2 from the atmosphere to soil dissolved inorganic carbon and supplying essential cations to roots, ERW can provide multiple benefits to cropping systems7. Nevertheless, as wollastonite application raises soil pH it may favour microbial activity and the deprotonation of organic compounds, thereby contributing to SOC mineralization, which partially offsets ERW benefits8. The extent to which SOC is mineralized depends, among other things, on the carbon use efficiency (CUE) of microbes and the persistence of SOC in the different soil pools, comprised of particulate (POM), dissolved (DOM) and mineral associated (MAOM) organic matter—the latest being considered as the most persistent physical fraction9. In non-acidic soils, calcium (Ca) supply in the form of CaCl2 can increase microbial CUE10. A proposed mechanism of improvement is that Ca favours the colonization of mineral surface by metabolically efficient organic matter decomposers, such as Actinomycetes (a group of bacteria characterized by the formation of hyphae), which deposit their metabolic byproducts on mineral surfaces, enhancing the MAOM pool10. Hence, we hypothesized that the supply of wollastonite will foster mineral surface colonization by hypha-forming bacteria, which will slow down SOC mineralization in non-acidic soils, resulting in SOC accrual, particularly in the MAOM. To test this hypothesis, we carried out an incubation experiment where we compared the supply of wollastonite with CaCl2, in addition to two widely used Ca soil amendments, a seashell calcium carbonate and gypsum. The experiment lasted 90 days and the mineralizability of Ca-treated soils of different textures was assessed with KOH traps. Dynamic combustion and loss on ignition (LOI) analyses were performed to quantify total organic and inorganic carbon content in the POM and MAOM fractions separated using a combined size and density fractionation method, which provided insights on the effect of Ca amendments chemically different on the accumulation and persistence of SOC in non-acidic soils of contrasting texture. The use of optical microscopy techniques enabled comparisons of hypha-forming bacteria abundance between treatments, thereby elucidating the involvement of Ca in microbial transformation of soil organic matter.

References:

1. Lehmann, J. et al. Persistence of soil organic carbon caused by functional complexity. Nat. Geosci. 13, 529–534 (2020).

2. Chappell, A., Baldock, J. & Sanderman, J. The global significance of omitting soil erosion from soil organic carbon cycling schemes. Nat. Clim. Change 6, 187–191 (2016).

3. Olson, K. R., Al-Kaisi, M., Lal, R. & Cihacek, L. Impact of soil erosion on soil organic carbon stocks. J. Soil and Water Conserv. 71, 61A-67A (2016).

4. Wang, M. et al. Global soil profiles indicate depth-dependent soil carbon losses under a warmer climate. Nat. Commun. 13, 5514 (2022).

5. Don, A. et al. Carbon sequestration in soils and climate change mitigation—Definitions and pitfalls. Glob. Change Biol. 30, e16983 (2024).

6. King, A. E. et al. Constraints on mineral-associated and particulate organic carbon response to regenerative management: carbon inputs and saturation deficit. Soil Tillage Res. 238, 106008 (2024).

7. Beerling, D. J. et al. Potential for large-scale CO2 removal via enhanced rock weathering with croplands. Nature 583, 242–248 (2020).

8. Yan, Y. et al. Wollastonite addition stimulates soil organic carbon mineralization: Evidences from 12 land-use types in subtropical China. Catena 225, 107031 (2023).

9. Cotrufo, M. F. & Lavallee, J. M. Chapter One - Soil organic matter formation, persistence, and functioning: A synthesis of current understanding to inform its conservation and regeneration. in Advances in Agronomy (ed. Sparks, D. L.) vol. 172 1–66 (Academic Press, 2022).

10. Shabtai, I. A. et al. Calcium promotes persistent soil organic matter by altering microbial transformation of plant litter. Nat. Commun. 14, 6609 (2023).