Influence of biochars on flux of N2O and CO2 from Ferrosol

Abstract

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 165 kg/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 3165 mg 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 636 mg 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 1705 mg N2O-N/m2 for 1 and 5% amendments. Amendment with BS biochar at 5% had the greatest impact, reducing emissions to 518 mg 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.