Biochar amendment suppresses N O emissions but has no impact on N site preference in an anaerobic soil.

RATIONALE

Biochar amendments often decrease N O gas production from soil, but the mechanisms and magnitudes are still not well characterized since N O can be produced via several different microbial pathways. We evaluated the influence of biochar amendment on N O emissions and N O isotopic composition, including N site preference (SP) under anaerobic conditions.

METHODS

An agricultural soil was incubated with differing levels of biochar. Incubations were conducted under anaerobic conditions for 10 days with and without acetylene, which inhibits N O reduction to N . The N O concentrations were measured every 2 days, the SPs were determined after 5 days of incubation, and the inorganic nitrogen concentrations were measured after the incubation.

RESULTS

The SP values with acetylene were consistent with N O production by bacterial denitrification and those without acetylene were consistent with bacterial denitrification that included N O reduction to N . There was no effect of biochar on N O production in the presence of acetylene between day 3 and day 10. However, in the absence of acetylene, soils incubated with 4% biochar produced less N O than soils with no biochar addition. Different amounts of biochar amendment did not change the SP values.

CONCLUSIONS

Our study used N O emission rates and SP values to understand biochar amendment mechanisms and demonstrated that biochar amendment reduces N O emissions by stimulating the last step of denitrification. It also suggested a possible shift in N O-reducing microbial taxa in 4% biochar samples.