Soil organic matter chemistry of surface soil differs under adaptive multi-paddock and continuous grazing in temperate pastures

<title>Abstract</title> <p> Adaptive multi-paddock (AMP) grazing has been associated with higher soil organic carbon (SOC) stocks in some grassland systems, but less is known about whether this management is accompanied by detectable changes in soil organic matter (SOM) chemistry. We used solid-state ¹³ C composite-pulse multiCP magic-angle-spinning nuclear magnetic resonance spectroscopy to compare hydrofluoric acid (HF)-treated bulk surface soils (0–15 cm) from paired AMP and continuous grazing (CG) pastures across five southern Ontario sites, with nearby cropland and woodlot soils included as land-use references. AMP and CG spectra were broadly similar, but AMP soils had higher relative carbohydrate-rich O-alkyl C (28.2% versus 26.3%) and alkyl C (21.2% versus 20.2%), whereas CG soils had higher phenolic C (6.2% versus 5.5%). Principal component analysis showed partial separation of AMP and CG samples, mainly along carbohydrate-rich O-alkyl, methoxy/amine, phenolic and aromatic regions. Across all land uses, AMP and CG remained more similar to each other than to cropland or woodlot soils. These results show that AMP grazing is associated with a measurable, but modest, shift in the functional-group composition of surface SOM. These data provide insight into SOM chemical composition that can aid interpretation of the mechanisms underlying grazing-related SOC patterns. </p>