The effect of a biochar temperature series on denitrification: which biochar properties matter?. (August 2019)

• Record Type: Journal Article
• Authors: Weldon, Simon; Rasse, Daniel P.; Budai, Alice; Tomic, Oliver; Dörsch, Peter
• Is Part Of: Soil biology and biochemistry. Volume 135(2019)
• Page Start: 173
• Page End: 183
• Publication Date: 2019-08
• Subjects: Biochar -- N2O -- NO -- Denitrification -- GHG mitigation -- Biochar properties; Soil biochemistry -- Periodicals; Soil biology -- Periodicals; Sols -- Biochimie -- Périodiques; Sols -- Biologie -- Périodiques; Sols -- Microbiologie -- Périodiques; Bodembiologie; Biochemie; 631.46
• DOI: 10.1016/j.soilbio.2019.04.018
• Languages: English
• ISSNs: 0038-0717

Abstract

Abstract: Biochar has been shown to reduce nitrous oxide (N2 O) emissions from soils, but the effect is highly variable across studies and the mechanisms are under debate. To improve our mechanistic understanding of biochar effects on N2 O emission, we monitored kinetics of NO, N2 O and N2 accumulation in anoxic slurries of a peat and a mineral soil, spiked with nitrate and amended with feedstock dried at 105 °C and biochar produced at 372, 416, 562 and 796 °C at five different doses. Both soils accumulated consistently less N2 O and NO in the presence of high-temperature chars (BC562 and BC796), which stimulated reduction of denitrification intermediates to N2, particularly in the acid peat. This effect appeared to be strongly linked to the degree of biochar carbonisation as predicted by the H:C ratio of the char. In addition, biochar surface area and pH were identified as important factors, whereas ash content and CEC played a minor role. At low pyrolysis temperature, the biochar effect was soil dependent, suppressing N2 O accumulation in the mineral soil, but enhancing it in the peat soil. This contrast was likely due to the labile carbon content of low temperature chars, which contributed to immobilise N in the mineral soil, but stimulated denitrification and N2 O emission in the peat soil. We conclude that biochar with a high degree of carbonisation, high pH and high surface area is best suited to supress N2 O emission from denitrification, while low temperature chars risk supporting incomplete denitrification. Highlights: Biochar produced over 416 °C consistently reduced N2O accumulation during denitrification. Denitrification response was soil dependent below this temperature. Carbonisation degree, pH and surface area best explained the response. Biochar affected total denitrification and not only the final conversion of N2O to N2.