Linking MAOM Formation from Lab to Field Scale - Conventional vs. Conservation Agricultural Management

Soil organic carbon (SOC) is a key regulator of soil functioning and ecosystem services, fundamental to nutrient cycling, soil structure, and long-term carbon sequestration¹. Within this pool, mineral associated organic matter (MAOM) represents the most persistent fraction, formed through interactions between microbially processed organic inputs and reactive mineral surfaces. We aim to advance the understanding of soil carbon dynamics across scales, from laboratory scale MAOM formation to ecosystem level patterns in managed agricultural soils. Specifically, we seek to identify which characteristics of the clay fraction, including clay minerals and metal oxides, govern MAOM formation under contrasting management regimes. To achieve these objectives, at the laboratory scale, we investigated interactions between organic matter inputs and mineral substrates in Loess soil using a controlled incubation experiment with defined mineral filled mesh bags, comparing straw amended and unamended soils. Following incubation, MAOM was characterized using nanoscale analysis, including thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and elemental analysis.  At the field scale, we assessed long-term agricultural systems under conventional and conservation management, incorporating organic inputs, service crops, and quantified SOC partitioning across Vertisol soil fractions and depths. Despite differences in scale and soil, consistent trends emerged, revealing enhanced association of organic carbon with mineral fractions in response to organic inputs¹. In the laboratory incubation, carbon accumulation was highest on goethite, lower on montmorillonite, and negligible on quartz, despite montmorillonite’s higher surface area. This pattern was further supported by greater mass loss during thermal digestion, indicating mineral specific enhancement of MAOM formation². At the field scale, conservation agriculture, which enhances organic inputs, showed a greater proportion of SOC associated with mineral fractions relative to particulate pools. While the clay sized fraction dominated MAOM storage, a measurable fraction of MAOM was also detected in the sand sized fraction, indicating additional carbon stabilization pathways under long-term management³. Linking these scales allows laboratory derived mechanisms to be interpreted in field conditions and, conversely, using field-scale patterns to refine mechanistic understanding of MAOM formation.

 

References

¹Mayer, M. et al. Dynamic stability of mineral-associated organic matter: enhanced stability and turnover through organic fertilization in a temperate agricultural topsoil. Soil Biol. Biochem. 184, 109095 (2023).

²Kirsten, M. et al. Iron oxides and aluminous clays selectively control soil carbon storage and stability in the humid tropics. Sci. Rep. 11, 5076 (2021).

³Li, Y. et al. Conservation tillage facilitates the accumulation of soil organic carbon fractions by affecting the microbial community in an eolian sandy soil. Front. Microbiol. 15, (2024).