Effects of feeding a pine-based biochar to beef cattle on subsequent manure nutrients, organic matter composition and greenhouse gas emissions.

Biochar in ruminant diets is being assessed as a method for simultaneously improving animal production and reducing enteric CH4 emissions, but little is known about subsequent biochar-manure interactions post-excretion. We examined chemical properties, greenhouse gas (GHG) emissions and organic matter (OM) composition during farm scale stockpiling (SP) or composting (CP) of manure from cattle that either received a pine-based biochar in their diet (BM) or did not (RM). Manure piles were monitored hourly for temperature and weekly for top surface CO2, N2O and CH4 fluxes over 90 d in a semiarid location near Lethbridge, AB, Canada. Results indicate that cumulative CO2, N2O and CH4 emissions were not affected by biochar, implying that BM was as labile as RM. The pH, total C (TC), NO3-N and Olsen P were also not influenced by biochar, although it was observed that NH4-N and OM extractability were both 13% lower in BM than RM. Solid-state 13C nuclear magnetic resonance (NMR) showed that biochar increased stockpile/compost aromaticity, yet it did not alter the bulk C speciation of manure OM. Further analysis by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed that dissolved OM was enriched by strongly reduced chemical constituents, with BM providing more humic-like OM precursors than RM. Inclusion of a pine-based biochar in cattle diets to generate BM is consistent with current trends in the circular economy, "closing the loop" in agricultural supply chains by returning C-rich organic amendments to croplands. Stockpiling/composting the resulting BM, however, may not provide a clear advantage over directly mixing low levels of biochar with manure. Further research is required to validate BM as a tool to reduce the C footprint of livestock waste management.

Molecular speciation and aromaticity of biochar-manure: Insights from elemental, stable isotope and solid-state DPMAS 13C 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 (CH4) 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% (BC0, BC0.5, BC1 and BC2) of diet dry matter. Manure was sampled three times over a 235 day feeding trial conducted in southern Alberta, Canada. Results showed that BC2 increased total C and the C/N ratio by 5.7 and 6.6% relative to BC0, respectively (P < 0.05), while total N exhibited a quadratic response from BC0 to BC2 (P = 0.005). Manure 15δN signatures, ranging from +3.83 to +7.34‰, were not affected (P > 0.05) by BC treatment. DPMAS 13C NMR revealed similar structural features among BC0 and BC2; 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 13C NMR spectra. Fused-ring domains, mainly pyrogenic-C, were increased by 1.56-fold at BC2 relative to BC0. 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.