Biochar mitigates the NO emissions from acidic soil by increasing the nosZ and nirK gene abundance and soil pH.

Nitrous oxide (NO) is a pervasive greenhouse gas, and soil management practices greatly affect its release into the atmosphere. Soil pH management (particularly increasing the pH) using biochar can seriously affect soil NO emissions. The current incubation experiment was conducted to explore the response of NO emissions from acidic soils using various doses of biochar. Soil with a pH of 5.48 was treated with rice straw biochar at different doses (0%, 1% and 2%) and incubated with 60% water-filled pore spaces (WFPS). The experiment was conducted in a completely randomized design (CRD) with three replications. The soil NO emissions, pH, NH-N, NO-N, microbial biomass carbon (MBC), and nosZ and nirK gene abundance were determined at various intervals throughout the study. The biochar application (2%) increased the soil pH (from 5.48 to 6.11), triggered the transformation of nitrogen, and augmented the abundance of nosZ and nirK genes. Higher magnitudes of cumulative soil NO emissions (48.60 μg kg) were noted in the control (no biochar) compared to 1% (28.10 μg kg) and 2% (14.50 μg kg) biochar application. The 2% biochar application more effectively decreased the soil NO emissions, mainly because of the increased nosZ and nirK gene abundance at higher soil pH levels. The findings suggest that the amelioration of acidic soil with rice straw biochar can considerably control soil NO emissions by elevating the soil pH and the abundance of nosZ and nirK genes.