Tuesday, October 18, 2011: 1:35 PM

Henry Gonzalez Convention Center, Room 210B, Concourse Level

Yunying Fang¹, Balwant Singh¹ and Bhupinder P. Singh², (1)Faculty of Agriculture, Food and Natural Resources, University of Sydney, Sydney, Australia
(2)PO Box 100, NSW Department of Primary Industries, Beecroft, Australia

Recorded Presentation Audio File

Biochar production and application to soil is increasingly discussed as a tool to sequester carbon (C) over centuries to millennia. Biochar may be highly stable in soil environment but the effects of soil mineralogy, soil C content and incubation temperature on biochar stability are not known. Moreover, there are conflicting reports about biochar effect on native soil C mineralisation, and the contrasting nature of biochar and soil types may explain some of the conflicting results. Our study is aimed at assessing the impacts of biochar–mineral interactions, soil C content, biochar chemical composition and incubation temperature on the stability of biochar-C and ‘native’ C in soils of contrasting properties.

We have employed a novel depleted-13C labelling approach to quantify decomposition of biochar and ‘native’ C in soils. Biochars were produced at two pyrolysis temperatures (450°C, 550°C) from woody biomass of 2 year-old Eucalyptus salinga that was depleted in 13C (δ13C -36.4‰). The biochars were incubated in four soils (collected from New South Wales, NSW; Queensland, Qld; South Australia, SA; Western Australia, WA) of contrasting properties (such as clay content and compositions, soil C content, pH) at three incubation temperatures (20 °C, 40 °C and 60 °C) for 6 months. The δ13C values of soils ranged from -17.5‰ to -27.7‰. The CO2 gas produced from biochar-amended and control soils was trapped in NaOH and these traps were sampled at regular intervals for respired-C and δ13C analyses.

The CO2-C mineralisation rate was initially high across all treatments, and then decreased and stabilised 30 days after incubation. The early results showed that the decomposition of carbon in biochar-amended soils increased with increasing soil temperature and varied with soil type, with NSW’s Oxisol produced the highest cumulative CO2-C followed by SA’s Entisol, WA’s Inceptisol and Qld’s Vertisol. The cumulative C produced from biochar450 amended soils was generally higher for the 450°C biochar than the 550°C biochar. The isotopic (δ13C) and spectroscopic analyses are being performed on gas, soil and/or biochar samples to quantify the decomposition rate of biochar-C and ‘native’ soil C, and the effect of soil mineralogy and soil carbon content on biochar C stability; these results will be presented at the conference.

See more from this Division: S11 Soils & Environmental Quality
See more from this Session: Environmental Functions of Biochar: I

291-3 Biochar Carbon Stability In Contrasting Soils As Influenced by Pyrolysis and Incubation Temperatures.