Impacts of Biochar-Manure Composts on Soil Nitrogen Retention and N2O Emissions Mitigation.

Synthetic chemical input-based modern agriculture has generated widespread issues on soil health and environmental quality. Making and using organic amendments in agricultural land have been acknowledged as a promising remediation strategy. Compared to ‘traditional’ compost, biochar compost is expected to unravel management-associated issues more effectively, due to biochar’s unique characteristics of (1) large surface area and porosity and (2) high ion exchange and adsorption capacity. We compared the impacts of chicken manure compost with (BM) or without (M) biochar as a composting additive on soil biological properties and processes in a laboratory microcosm experiment. Compared to the M treatment, BM significantly reduced soil CO₂ and N₂O emissions by 35% and 25%, respectively, over the experimental period. The ¹⁵N-N₂O site preference was ~10‰ for M and ~25‰ for BM, suggesting that biological sources of soil N₂O emissions also differed between M and BM. Although M and BM addition enhanced soil inorganic N and water-extractable organic N, the enhancement was slightly lower in BM than M treatment. Soil glucosaminidase activity and nirK gene abundance were also lower in BM than M treatments. However, soil peroxidase activity and the abundance of ammonium oxidizing archaea were greater in BM than M treatments. Our data demonstrated that biochar as a composting additive could substantially reduce soil N₂O emissions via controls on the activities of microbial functional groups and soil N availability.