Authors: R J Harper M Tibbett
Publish Date: 2013/01/26
Volume: 368, Issue: 1-2, Pages: 641-648
Abstract
Current estimates of soil organic carbon SOC are based largely on surficial measurements to depths of 03 to 1 m Many of the world’s soils greatly exceed 1 m depth and there are numerous reports of biological activity to depths of many metres Although SOC storage to depths of up to 8 m has been previously reported the extent to which SOC is stored at deeper depths in soil profiles is currently unknown This paper aims to provide the first detailed analysis of these previously unreported stores of SOCSoils from five sites in the deeply weathered regolith in the Yilgarn Craton of southwestern Australia were sampled and analysed for total organic carbon by combustion chromatography These soils ranged between 5 and 38 m mean 21 m depth to bedrock and had been either recently reforested with Pinus pinaster or were under agriculture Sites had a mean annual rainfall of between 399 and 583 mm yr−1The mean SOC concentration across all sites was 230 ± 026 se 041 ± 005 and 023 ± 004 in the surface 01 01–05 and 05 to 10 m increments respectively The mean value between 1 and 5 m was 012 ± 001 whereas between 5 and 35 m the values decreased from 004 ± 0002 to 003 ± 0003 Mean SOC mass densities for each of the five locations varied from 218–375 kg C m−2 and were in toto two to five times greater than would be reported with sampling to a depth of 05 mThis finding may have major implications for estimates of global carbon storage and modelling of the potential global impacts of climate change and landuse change on carbon cycles The paper demonstrates the need for a reassessment of the current arbitrary shallow soil sampling depths for assessing carbon stocks a revision of global SOC estimates and elucidation of the composition and fate of deep carbon in response to land use and climate changeWe thank David Chittleborough Jock Churchman Guy Kirk Stan Sochacki Bernard Dell Chris Mitchell Rod Keenan Keith Smettem and two anonymous reviewers for useful comments Ian Truckell Cranfield University for preparing the Figures Alex Winter Forest Products Commission Western Australia Marianne Harkins CSBP Michael Smirk and Evonne Walker UWA for assistance in the field and laboratory and all landholders for access to sites Drilling was undertaken by the Forest Products Commission Western Australia as part of the Australian National Action Plan for Salinity and Water Quality project “Strategic Tree Farming”
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