Insight into the effects of biochar on manure composting: Evidence supporting the relationship between N₂O emission and denitrifying community(Article)

• ^aInstitute of Environmental Science and Technology, Zhejiang University, 866 Yuhangtang Road, Hangzhou 310058, China
• ^bCallaghan Innovation Research Ltd, University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand
• ^cSchool of Environmental and Resource Sciences, Zhejiang A and F University, Lin’an, Hangzhou 311300, China

Abstract

Although nitrous oxide (N₂O) emissions from composting contribute to the accelerated greenhouse effect, it is difficult to implement practical methods to mitigate these emissions. In this study, the effects of biochar amendment during pig manure composting were investigated to evaluate the inter-relationships between N₂O emission and the abundance of denitrifying bacteria. Analytical results from two pilot composting treatments with (PWSB, pig manure + wood chips + sawdust + biochar) or without (PWS, pig manure + wood chips + sawdust) biochar (3% w/w) demonstrated that biochar amendment not only lowered NO₂ ^–-N concentrations but also lowered the total N₂O emissions from pig manure composting, especially during the later stages. Quantification of functional genes involved in denitrification and Spearman rank correlations matrix revealed that the N₂O emission rates correlated with the abundance of nosZ, nirK, and nirS genes. Biochar-amended pig manure had a higher pH and a lower moisture content. Biochar amendment altered the abundance of denitrifying bacteria significantly; less N₂O-producing and more N₂O-consuming bacteria were present in the PWSB, and this significantly lowered N₂O emissions in the maturation phase. Together, the results demonstrate that biochar amendment could be a novel greenhouse gas mitigation strategy during pig manure composting.