Novel strategies for biochar application to densely populated livestock regions in North America –

Biochar is now considered a global applicable resource to address the increasing complexity of modern-day farming from an agro-environmental perspective. However, its use in ruminant husbandry (i.e., as animal feed additive) is currently only a potential management strategy that needs more systematic research; particularly when considering manure-induced secondary effects on soil fertility and soil-borne greenhouse gas (GHG) emissions. A 70-day soil column experiment (21°C; 60-80% WHC) was conducted within two surface (0-15 cm) prairie-fertile Mollisols of contrasting texture (i.e., sandy clay loam and clayey) to evaluate the effects of pine
wood biochar (3 Mg ha ) on cumulative GHG emissions and related fertility attributes in the presence or absence of cattle manure (120 Mg ha ). We compared ¦ve treatments: (i) nonamended soil (CK); (ii) soil amended with pine wood biochar (B); (iii) soil amended with beef cattle manure (i.e., manure from cattle on control diet) (M); (iv) soil amended with biochar manure (i.e., manure from cattle on control diet supplemented with 2% of diet dry matter as biochar) (BM); and (v) soil amended with B and M at the aforementioned rates (B+M). Regardless of soil type, application of biochar-only did not alter cumulative CO , N O, or CH emissions over CK, implying that addition of pyrolyzed-C at low application rates (<3 Mg ha ) has little effect on the cycling of soil nutrients and storage of soil organic matter (OM). Contrarily, amending both soils with manure or biochar-manure mixtures increased (P<0.05) cumulative CO (2.2 to 3.8-fold) and CH (17.6 to 34.6-fold) emissions over CK and B, mainly through a large, enriched pool of dissolved OM. After 70 days, BM increased PO -P availability over M and B+M treated soils, suggesting that passage of biochar through the ruminant digestive tract may have improved the agronomic value of beef cattle manure. We conclude that biochar and manure and/or biochar manure have contrasting short-term effects on the biogeochemistry of Mollisols. At relatively low application rates, biochar does not necessarily counterbalance manure-derived inputs. Although
BM did not mitigate the flux of GHGs over M, biochar-manure has the potential to improve nutrient recycling in temperate agro-ecosystems.