Nitrous oxide emission reduction in temperate biochar-amended soils

Abstract. Biochar, a pyrolysis product of organic residues, is an amendment for agricultural soils to improve soil fertility, sequester CO₂ and reduce greenhouse gas (GHG) emissions. In highly weathered tropical soils laboratory incubations of soil-biochar mixtures revealed substantial reductions for nitrous oxide (N₂O) and carbon dioxide (CO₂). In contrast, evidence is scarce for temperate soils. In a three-factorial laboratory incubation experiment two different temperate agricultural soils were amended with green waste and coffee grounds biochar. N₂O and CO₂ emissions were measured at the beginning and end of a three month incubation. The experiments were conducted under three different conditions (no additional nutrients, glucose addition, and nitrate and glucose addition) representing different field conditions. We found mean N₂O emission reductions of 60 % compared to soils without addition of biochar. The reduction depended on biochar type and soil type as well as on the age of the samples. CO₂ emissions were slightly reduced, too. NO₃^– but not NH₄⁺ concentrations were significantly reduced shortly after biochar incorporation. Despite the highly significant suppression of N₂O emissions biochar effects should not be transferred one-to-one to field conditions but need to be tested accordingly.