Estimating maximum fine-fraction organic carbon in UK grasslands
Date
2021-01-27
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Publisher
Copernicus Publications for European Geosciences Union
Abstract
Soil organic carbon (SOC) sequestration across
agroecosystems worldwide can contribute to mitigate the effects
of climate change by reducing levels of atmospheric
CO2. Stabilisation of organic carbon (OC) in the fine soil
fraction (<20 μm) is considered an important long-term
store of SOC, and the saturation deficit (difference between
measured OC and estimated maximum OC in the fine fraction)
is frequently used to assess SOC sequestration potential
following the linear regression equation developed by Hassink
(1997). However, this approach is often taken without
any assessment of the fit of the equation to the soils being
studied. The statistical limitations of linear regression have
previously been noted, giving rise to the proposed use of
boundary line (BL) analysis and quantile regression (QR)
to provide more robust estimates of maximum SOC stabilisation.
The objectives of this work were to assess the
suitability of the Hassink (1997) equation to estimate maximum
fine-fraction OC in UK grassland soils of varying
sward ages and to evaluate the linear regression, boundary
line and quantile regression methods to estimate maximum
fine-fraction OC. A chronosequence of 10 grasslands was
sampled, in order to assess the relationship between sward
age (time since the last reseeding event) and the measured
and predicted maximum fine-fraction OC. Significantly different
regression equations show that the Hassink (1997)
equation does not accurately reflect maximum fine-fraction
OC in UK grasslands when determined using the proportion
of the fine soil fraction (<20 μm, %) and measured finefraction
OC (g C per kg soil). The QR estimate of maximum
SOC stabilisation was almost double that of the linear
regression and BL analysis (0.89 0.074, 0.43 0.017
and 0.57 0.052 gC per kg soil, respectively). Sward age
had an inconsistent effect on the measured variables and potential
maximum fine-fraction OC. Fine-fraction OC across
the grasslands made up 4.5% to 55.9% of total SOC, implying
that there may be either high potential for additional C
sequestration in the fine fraction of these soils or that protection
in aggregates is predominant in these grassland soils.
This work highlights the need to ensure that methods used to
predict maximum fine-fraction OC reflect the soil in situ, resulting
in more accurate assessments of carbon sequestration
potential.
Description
Publication history: Accepted - 24 November 2021; Published - 27 January 2021.
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Citation
Paterson, K.C., Cloy, J.M., Rees, R.M., Baggs, E.M., Martineau, H., Fornara, D., Macdonald, A.J. and Buckingham, S. (2021) ‘Estimating maximum fine-fraction organic carbon in UK grasslands’, Biogeosciences. Copernicus GmbH. doi:10.5194/bg-18-605-2021