Association of Organic Carbon With Reactive Iron Oxides Driven by Soil pH at the Global Scale

Summary

This global-scale analysis demonstrates that soil pH is the primary edaphic driver of organic carbon association with reactive iron oxides across diverse soil types. Using NEON network data and published soil observations, the authors identified a strong non-linear relationship: Fe-associated C increases markedly as pH drops below 4.2, but changes little in less acidic soils. A liming experiment in acidic Oxisol further confirmed that pH elevation reduces Fe-C formation, suggesting pH as a mechanistic control on this important mechanism of terrestrial carbon storage.

UK applicability

The findings are relevant to UK soil management insofar as many UK soils have pH > 4.2 (particularly agricultural soils treated with lime), where the study predicts minimal pH-driven variation in Fe-associated C. However, acidic upland and heathland soils (pH < 4.2) may be more sensitive to pH-driven changes in Fe-C dynamics, with implications for carbon sequestration strategies in these systems.

Key measures

Fe-associated carbon concentration (g kg⁻¹ soil); soil pH; response to liming treatment in microcosm

Outcomes reported

The study quantified Fe-associated carbon across diverse soil types using NEON and published soil data, and experimentally tested the effect of pH manipulation on Fe-C association in acidic soils. Fe-associated C ranged from 0–20 g kg⁻¹ soil, with a strong pH-dependent relationship.

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