Canola straw biochars produced under different pyrolysis temperatures and nitrapyrin independently affected cropland soil nitrous oxide emissions

The effect of biochar and nitrapyrin (a nitrification inhibitor) applications on nitrous oxide (N₂O) emissions from a cropland soil was studied in a 35-day incubation experiment. The biochars were produced using canola (Brassica napus L.) straw under two pyrolysis temperatures: 300 (BC300) and 700 °C (BC700). Biochars (20 g kg⁻¹ soil) and nitrapyrin (80 mg kg⁻¹ soil) were applied alone or in combination. The cumulative N₂O emissions were affected by both biochar and nitrapyrin applications (p < 0.05, same below) but not by their interaction. Cumulative N₂O emissions were not affected by BC700, but were increased by BC300, as compared with the CK treatment (no biochar addition). Nitrapyrin significantly decreased cumulative N₂O emissions by inhibiting nitrification, whether biochar was applied or not. There were positive relationships (p < 0.05) between cumulative N₂O emissions and soil microbial biomass carbon to nitrogen ratio, nitrate and dissolved organic nitrogen concentrations, and net nitrification rates. Our results show that biochars need to be appropriately selected (such as the use of BC700) that do not increase N₂O emissions, while the effectiveness of nitrapyrin in reducing N₂O emissions was not affected by the co-application of biochars. We conclude that the co-application of biochar and nitrapyrin may be able to both increase soil C sequestration by the addition of stable C contained in the biochar and reduce N₂O emissions from agricultural production systems.