Molecular speciation and aromaticity of biochar-manure: Insights from elemental, stable isotope and solid-state DPMAS C NMR analyses.

The use of biochar (BC) in feedlot cattle diets has recently been explored as an approach to simultaneously improving animal production and reducing enteric methane (CH) emissions. This study examines the impact of BC on manure properties and whether BC affects manure composition and carbon (C) and nitrogen (N) outputs from feedlot steers offered a barley-based diet with BC at 0.0, 0.5, 1.0 and 2.0% (BC, BC, BC and BC) of diet dry matter. Manure was sampled three times over a 235 day feeding trial conducted in southern Alberta, Canada. Results showed that BC increased total C and the C/N ratio by 5.7 and 6.6% relative to BC, respectively (P < 0.05), while total N exhibited a quadratic response from BC to BC (P = 0.005). Manure δN signatures, ranging from +3.83 to +7.34‰, were not affected (P > 0.05) by BC treatment. DPMAS C NMR revealed similar structural features among BC and BC; indigestible BC had a minor impact on the bulk-C speciation of manure organic matter (OM). Compositional changes were limited to the aromatic-C region of the C NMR spectra. Fused-ring domains, mainly pyrogenic-C, were increased by 1.56-fold at BC relative to BC. Overall, results demonstrated that BC stabilizes recalcitrant-C in manure OM, potentially sequestering soil-C when applied to croplands. This approach provides an added value to its use in ruminant diets, mainly from a nutrient cycling perspective. However, whole-farm studies are further required to validate the incorporation of BC into beef production systems.