Rice Rusk-Derived Biochar Suppressed N₂O Emission from Acidic Arable Soil by Inhibiting Nitrate Reduction

Abstract: The study aims to explore the potential mechanisms of rice husk-derived biochar’s effect on acidic arable soil N₂O emission during denitrification. The microcosm experiment with four biochar addition rates (0%, 2%, 5%, and 10%, w/w) was carried out for 17 days consecutively under the condition of facilitating denitrification. N₂O emission rate and the changes of soil pH, electrical conductivity (EC), inorganic nitrogen, and dissolved organic carbon (DOC) contents during incubation were explored. Moreover, N₂O and N₂ distribution pattern, as the end products of denitrification, was determined by acetylene inhibition method, and the effect of biochar on soil organic carbon mineralization was also studied by trapping CO₂ in NaOH solution. The cumulative N₂O emission of 0%, 2%, 5%, and 10% treatments was 100.2 ± 2.13, 40.7 ± 5.00, 4.25 ± 0.10, and 0.03 ± 0.002 µg N₂O-N g⁻¹ dry soil, respectively. The biochar significantly inhibited N₂O emission from the N-fertilized acidic arable soil. The changes of soil pH, EC, inorganic nitrogen, and DOC contents and the distribution pattern of N₂O and N₂ indicated that the potential mechanism of biochar inhibiting N₂O emission was that NO₃⁻ reduction was blocked by biochar during denitrification. Furtherly, the study showed that the biochar significantly promoted DOC mineralization of the acidic arable soil, and the effect was enhanced with biochar addition rate increasing from 2 to 10%. It was biochar’s promotion effect on DOC mineralization that resulted in C limitation during denitrification and then prevented NO₃⁻ reduction and suppressed N₂O emission from the acidic arable soil. Graphical abstract: [Figure not available: see fulltext.]