Spatial variation of subsoil organic carbon concentration and thermal fractions under agricultural landscapes

Rawlins, Barry; Barker, Monica; Lark, Murray; Wagner, Doris; Kemp, Simon ORCID: 2012 Spatial variation of subsoil organic carbon concentration and thermal fractions under agricultural landscapes. [Poster] In: Eurosoil 2012, Bari, Italy, 2-7 July 2012. British Geological Survey. (Unpublished)

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From previous research on spatial variation of topsoil carbon concentrations, variance components based on loss-on-ignition analysis increased by an order of magnitude from i) analytical plus subsampling, to ii) short-scale (20 metre: paired samples), to iii) medium-scale (>1000m). There is little knowledge concerning the scales over which subsoil (35 to 50 cm depth) organic carbon (SSOC) concentrations – and their biogeochemical fractions – vary. We measured total SSOC concentration by combustion (elemental analysis) based on the <150 micron aggregate size fractions for samples collected from a total of 122 grassland or arable sites. We measured other soil properties (total Ca, pH and dithionite iron (Fe(d)) concentrations, clay) for each sample which may account – through various mechanisms – for preservation of SSOC. We subjected half of the paired samples to thermal analysis to estimate labile and resistant biogeochemical fractions. SSOC variance components i) and ii) were of the same magnitude; the difference [to that observed for topsoil] is likely due to the quantity of subsample used in the two analytical methods. As for topsoil, variance in SSOC increased by an order of magnitude between components ii) and iii). Soil Group accounted for a statistically significant component of the variance in SSOC. Three soil properties (total Ca, pH and Fe(d)) concentrations accounted for 30% of the variance in log SSOC; clay content was not significant. The linear correlation of log SSOC concentration between paired sites was substantially weaker (r=0.39) than the log ratio of two thermal fractions for the same paired samples (r=0.62). This finding has implications for understanding SSOC turnover and sequestration.

Item Type: Publication - Conference Item (Poster)
Programmes: BGS Programmes 2010 > Land Use, Planning and Development
NORA Subject Terms: Ecology and Environment
Date made live: 22 Jun 2012 15:01 +0 (UTC)

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