The effect of biochar addition on N2O and CO2 emissions from a sandy loam soil – The role of soil aeration

Biochar application to soil has significant potential as a climate change mitigation strategy, due to its recalcitrant C content and observed effect to suppress soil greenhouse gas emissions such as nitrous oxide (N2O). Increased soil aeration following biochar amendment may contribute to this suppr...

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Published in:Soil biology & biochemistry 2012-08, Vol.51, p.125-134
Main Authors: Case, Sean D.C., McNamara, Niall P., Reay, David S., Whitaker, Jeanette
Format: Article
Language:English
Subjects:
Agronomy. Soil science and plant productions
Biochar
Biochemistry and biology
Biological and medical sciences
Charcoal
Chemical, physicochemical, biochemical and biological properties
Climate change
Fundamental and applied biological sciences. Psychology
Physics, chemistry, biochemistry and biology of agricultural and forest soils
Soil science
Water holding capacity
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Summary:Biochar application to soil has significant potential as a climate change mitigation strategy, due to its recalcitrant C content and observed effect to suppress soil greenhouse gas emissions such as nitrous oxide (N2O). Increased soil aeration following biochar amendment may contribute to this suppression. Soil cores from a Miscanthus X. giganteus plantation were amended with hardwood biochar at a rate of 2% dry soil weight (22 t ha−1). The cores were incubated at three different temperatures (4, 10 and 16 °C) for 126 days, maintained field moist and half subjected to periodic wetting events. Cumulative N2O production was consistently suppressed by at least 49% with biochar amendment within 48 h of wetting at 10 and 16 °C. We concluded that hardwood biochar suppressed soil N2O emissions following wetting at a range of field-relevant temperatures over four months. We hypothesised that this was due to biochar increasing soil aeration at relatively high moisture contents by increasing the water holding capacity (WHC) of the soil; however, this hypothesis was rejected. We found that 5% and 10% biochar amendment increased soil WHC. Also, 10% biochar amendment decreased bulk density of the soil. Sealed incubations were performed with biochar added at 0–10 % of dry soil weight and wetted to a uniform 87% WHC (78% WFPS). Cumulative N2O production within 60 h of wetting was 19, 19, 73 and 98% lower than the biochar-free control in the 1, 2, 5 and 10% biochar treatments respectively. We conclude that high levels of biochar amendment may change soil physical properties, but that the enhancement of soil aeration by biochar incorporation makes only a minimal contribution to the suppression of N2O emissions from a sandy loam soil. We suggest that microbial or physical immobilisation of NO3− in soil following biochar addition may significantly contribute to the suppression of soil N2O emissions. ► We investigate the effect of biochar addition on soil nitrous oxide (N2O) emissions. ► Soil N2O production is suppressed by 49% with biochar within 48 h of wetting. ► Increased soil aeration resulting from biochar addition cannot explain this effect. ► Extractable nitrate concentrations in soil decrease with biochar addition. ► We suggest that immobilisation of nitrate is increased in biochar amended soil.
ISSN:0038-0717
1879-3428
DOI:10.1016/j.soilbio.2012.03.017