Organo-mineral associations largely contribute to the stabilization of century-old pyrogenic organic matter in cropland soils

Understanding the processes underlying carbon (C) stability in soils is of utmost importance context climate change. In this setting, biochar often studied for its persistence and reported to have positive impacts on soil fertility. Whilst recent research has mostly focused short-term effects amendments soil, a better understanding long-term needed. Our study focuses agricultural enriched charcoal residues, produced preindustrial kiln sites ca. 220 years ago, as proxy aged biochar. aim understand governing pyrogenic organic matter (PyOM) cultivated soils. To achieve this, we focus i) effect PyOM aggregation, ii) distribution amongst fractions iii) chemical thermal properties. For purpose, combined particle size-density fractionation with elemental analyses topsoil samples collected (CHAR) adjacent reference (REF) conventionally cropped field Wallonia (Belgium). The presence resulted 91 ± 34% higher C content CHAR than REF soils, which 84 94% was 6 16% additional non-PyOM. macroaggregation promoted at expense microaggregation (CHARMACRO = 48.9 12.8; CHARMICRO 25.5 8.3 g 100 g?1 soil) whereas these were similar (REFMACRO 41.3 9.5; REFMICRO 36.0 8.7 soil). Elemental revealed that did not only occur free light but also occluded aggregates or sorbed onto mineral phases (56.4 22.9% total PyOM) suggesting may be further stabilized through organo-mineral associations. Century-old showed increased H:C O:C atomic ratios compared recently pyrolyzed OM, particularly opposed fractions, vouching functionalization surfaces. Furthermore, regardless high contents C:N between dominated suggested amounts N-rich non-PyOM rich results demonstrate that, over centuries plays an active role aggregation patterns. We conclude century old broken down from coarse fine particles, surfaces contributes Beyond intrinsic recalcitrance, enhanced by occlusion sorption processes.