Nitrous oxide mitigation potential of biochar derived from agricultural and forest biomass: Effects of feedstock composition and pyrolysis temperature

Biochar application to soil has been promoted to mitigate climate change by reducing greenhouse gas (GHG) emissions, yet significant uncertainty exists in quantifying soil nitrous oxide (N₂O) emissions from biochar-amended soils. We evaluated soil N₂O emissions from soils amended with biochar prepared from diverse agricultural and forest biomass and underlying biogeochemical mechanisms using long-term soil incubations and empirical modeling. Biochars compared were pinewood pyrolyzed at 460°C (PB460), pinewood pyrolyzed at 500°C (PB500), pinewood pyrolyzed at 700°C (PB700), pine bark gasified at 760°C (GB760), cattle manure pyrolyzed at 500°C (CM500), pecan wood pyrolyzed at 500°C (PW500), hemp wood pyrolyzed at 500°C (HW500), and no biochar control (CTRL). Three nonlinear empirical models, first-order kinetic model (FOKM), double exponential model (DEM), and first-order logistic (FLOG) model, were tested to evaluate N₂O emissions from various biochar-amended soils. The PB700 was the most efficient in reducing N₂O emissions, with 24% less total cumulative N₂O emissions than CTRL. In contrast, the CM500 amendment resulted in 74% greater cumulative N₂O-N emissions than CTRL (10.4 mg kg^-1) and 102%-107% greater emissions than plant-based agricultural biochars. Among models compared to study N₂O emissions dynamics, the FLOG model best described the biochar N₂O emissions irrespective of the biochar types. It showed the largest labile nitrogen pool (N_l) in CM500 among all biochars, and the cumulative N₂O emission was positively correlated with N_l (r = 0.85; p < 0.001). Labile N content in biomass and pyrolysis temperature determined the N₂O emissions mitigation potential in biochar-amended soils.