Influence of biochars on flux of N₂O and CO₂ from Ferrosol

• Published in: Australian journal of soil research Vol. 48; no. 7; pp. 555 - 568
• Main Authors: van Zwieten, L, Kimber, S, Morris, S, Downie, A, Berger, E, Rust, J, Scheer, C
• Format: Journal Article
• Language: English
• Published: Collingwood, Victoria: CSIRO Publishing 2010
• Subjects: biochar; biosolids; greenwaste; mechanism; nitrous oxide; papermill; poultry manure; slow pyrolysis; soil properties
• ISSN: 0004-9573; 1446-568X
• DOI: 10.1071/sr10004

Biochars produced by slow pyrolysis of greenwaste (GW), poultry litter (PL), papermill waste (PS), and biosolids (BS) were shown to reduce N₂O emissions from an acidic Ferrosol. Similar reductions were observed for the untreated GW feedstock. Soil was amended with biochar or feedstock giving application rates of 1 and 5%. Following an initial incubation, nitrogen (N) was added at 165kg/ha as urea. Microcosms were again incubated before being brought to 100% water-filled porosity and held at this water content for a further 47 days. The flooding phase accounted for the majority (<80%) of total N₂O emissions. The control soil released 3165mg N₂O-N/m², or 15.1% of the available N as N₂O. Amendment with 1 and 5% GW feedstock significantly reduced emissions to 1470 and 636mg N₂O-N/m², respectively. This was equivalent to 8.6 and 3.8% of applied N. The GW biochar produced at 350°C was least effective in reducing emissions, resulting in 1625 and 1705mg N₂O-N/m² for 1 and 5% amendments. Amendment with BS biochar at 5% had the greatest impact, reducing emissions to 518mg N₂O-N/m², or 2.2% of the applied N over the incubation period. Metabolic activity as measured by CO₂ production could not explain the differences in N₂O emissions between controls and amendments, nor could NH₄⁺ or NO₃⁻ concentrations in biochar-amended soils. A decrease in NH₄⁺ and NO₃⁻ following GW feedstock application is likely to have been responsible for reducing N₂O emissions from this amendment. Reduction in N₂O emissions from the biochar-amended soils was attributed to increased adsorption of NO₃⁻. Small reductions are possible due to improved aeration and porosity leading to lower levels of denitrification and N₂O emissions. Alternatively, increased pH was observed, which can drive denitrification through to dinitrogen during soil flooding.