Soil carbon variability in Central NSW
I. Grange & A. Rawson
University of Sydney, Orange, NSW, Australia
Introduction
Soils are spatially variable even over short distances (Beckett & Webster 1971). Soil organic carbon is one such property,
influenced by a number of controlling parameters operating at the
the macromacro-, mesomeso- and micromicro-scales.
Clearance of natural vegetation has been extensively carried out in NSW. This has inevitably impacted on soil carbon
dynamics resulting in decreased soil carbon stocks and increased greenhouse gas emissions (CO2). Vegetation type and
distribution, of nonnon-disturbed and disturbed areas are of particular interest, enabling
enabling better estimation of CO2 emissions and
associated mechanisms.
Objectives
The broad objectives of the research are to better characterize soil carbon variability and optimal sampling regimes, and
identify the principal controlling parameters at different scales,
scales, with the information gained being used to refine and further
develop understanding of carbon in the environment, in part through
through the use of models.
Study site
CP
NSS
SEH
SB
Example of soil carbon variability in NSW
The following data illustrate the variability in soil organic carbon
carbon found in similar
environments i.e. the same soil type (Red Kandosol)
Kandosol) and land use under Bimble box
grassy woodland within the same region (Cobar
(Cobar Peneplain biogeographic region).
Note: CP5 has the second lowest C density, but the highest standing dry
dry matter + litter
(adapted from Murphy et al. 2003).
Site number
SOC mean
(t/ha/30cm)
SD
SE
CV
The figure shows: the main WW-E macromacroscale transect; four mesomeso-scale study
areas within biogeographic regions;
mesomeso-/ micromicro-scale replicate quadrats
(25 x 25m – Mckenzie et al. 2000).
Representative replicate paired sites for
further micromicro-scale analysis & longlong-term
monitoring will also be selected (Image
from: Landsat ETM 2002 25m 1:2m,
AGO 2004).
Predicted changes in the contents of soil carbon fractions over time
when a cropping system is converted to pasture. The red circles
indicate that total SOC is the same at two separate times, but the
the
corresponding SOC fractions, which are associated with different soil
functions (e.g. aggregate stability), are significantly different
different (adapted
from Baldock & Skjemstad 1999).
Standing dry matter
+ litter (t/ha)
CP1
28.96
5.47
2.45
19.82
8.28
CP2
39.48
7.32
3.28
18.54
12.74
CP3
32.80
3.70
1.67
11.28
9.08
CP4
40.35
5.86
2.62
14.52
7.82
CP5
31.71
4.34
1.94
13.69
15.83
CP6
39.69
4.83
2.16
12.17
13.84
Specific aims
PairedPaired-sites
To assess the relative importance of the
following controlling parameters on the
levels and distribution of soil carbon in the
environment:
ƒ Plant litter quantity / quality (ground
cover types)
ƒ Topography (terrain position &
elevation)
ƒ Climate: rain & temperature (macro(macroscale, longitudinal & latitudinal)
ƒ Soil type (mineralogy / geology)
ƒ Management practices
ƒ Fire (frequency & distribution)
PairedPaired-sites will enable
assessment of changes
in soil carbon stocks over
time resulting from land
use changes.
Identification of good
pairedpaired-sites will be a key
aim of this project
enabling improved
validation of soil carbon
models and an
opportunity for longlong-term
monitoring.
Example of a paired site showing undisturbed woodland area on
left and cultivated area on the right (Murphy et al. 2003).
Initial conclusions
References
ƒ Soil carbon variability is not easily
explained by corresponding litter data
AGO 2004, CDCD-ROM, Australia 19721972-2002: A view from space. Australian Greenhouse Office,
Canberra 2004. Version 1.0. Also available
ƒ Management histories may go some way
toward explaining differences in soil carbon
variability
ƒ Plant species are in association with
different soil carbon levels - possible cause
and effect
Expected Outcomes
Baldock JA & Skjemstad JO 1999, ‘Soil organic carbon/soil organic matter’, in KI Peverill,
Peverill, LA
Sparrow & DJ Reuter (eds.), Soil Analysis: an interpretation manual,
manual, CSIRO Publishing,
Melbourne.
Beckett PHT & Webster R 1971 Soil variability: a review. Soils and Fertilizers vol. 34, pp. 11-15
McKenzie N, Ryan P, Fogarty P & Wood J 2000, Sampling, measurement and analytical protocols
for carbon estimation in soil, litter and coarse woody debris, National Carbon Accounting System
Technical Report No. 14. Australian Greenhouse Office, Canberra.
Murphy B, Rawson A, Ravenscroft L, Rankin M & Millard R 2003, Paired site sampling for soil
carbon estimation – New South Wales, National Carbon Accounting System Technical Report No.
34. Australian Greenhouse Office, Commonwealth of Australia.
This work will ultimately allow for the development of sustainable
sustainable management practices with the potential to sequester
larger amounts of Atmospheric CO2 or to allow for suitable adjustments in soil carbon emissions that
that can effect future
climate change.