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TECHNICAL REPORT
GREENHOUSE ALLIES PROJECT
Measurement of carbon sequestration
in small non-industrial forest plantations.
(continued)
6 Soils.
The soil sampling effort was limited by time and money. It was decided at the May
1999 Workshop that a set of paired pits (one in the plantation within the ripped rows,
if present) and one in an adjacent paddock, deemed to be representative of
conditions prior to establishment, be dug at each site to a depth of approximately
one metre and sampled every 10 cm. Soil carbon content in tonnes per hectare was
calculated from a percentage carbon content using a LECO autoanalyser (accuracy
0.05%) and the bulk density of the sample.
The depth sampling illustrated the limitations of lack of replication at each site, but
demonstrated the range of values that might be expected and the key horizons at
which future sampling could be concentrated (Figures 21 to 23).
Figure 21a: Soil profiles of percentage carbon content (left) and estimated carbon content for
plantation and paddock soils of three properties in the Northern Rivers region of New South
Wales. Fayle and Harvey-Jones are on basalt-derived soils planted with rainforest species and the
Mebbin site is planted with eucalypt blocks and is on metamorphics.
Figure 21b: Soil profiles of percentage carbon content
for plantation and paddock soils of two properties
Wales. Two paired pits are shown for Johnston’s property,
in krasnozem soil at Lascelles.
Figure 21c: Soil profiles of percentage carbon content (left) and estimated carbon content (right) for
plantation and paddock soils of two properties in the Northern Rivers region of New South Wales.
Moody’s property is in a similar area to Johnston’s and the plantation at Rocky Creek Dam is on
krasnozem, last grazed thirty years ago.
Figure 22a: Soil profiles of percentage carbon content (left) and estimated carbon content (right)
for plantation and paddock soils of three properties in the Mid-North Coast region of New South
Wales. The plantation at Henderson’s property was not measured.
Figure 22b: Soil profiles of percentage carbon content (left) and estimated carbon content (right)
for plantation and paddock soils of two properties in the Mid-North Coast region of New South
Wales. Two soil pits were dug close to one another on the Manners property to investigate the degree
of variation across the site. The pattern in the plantation is similar, but the amounts are different.
The paddock site shows considerable depletion in surface carbon at one 2b, only metres away from
2a.
Figure 22c: Soil profiles of percentage carbon content (left) and estimated carbon content (right) for
plantation and paddock soils of three properties in the Mid-North Coast region of New South
Wales. Only one pit was dug, in the paddock, at Williams property. A similar pattern to that
noticeable at Manners 2b is apparent in the paddock soil at Worth.
Figure 23: Soil profiles of percentage carbon content (left) and estimated carbon content (right) for
plantation and paddock soils of three properties in the New England region of New South Wales.
The surface carbon content is much lower at Taylor’s property than at the other two, it being a 1990
planting.
The amount of variation within a property is not surprising, and the results shown
for Manners and Johnston illustrate this. The amount of variation in paddock soil
was tested at the Thomas property on the Mid-North Coast along a distance of 1.4
km. Here the amount of carbon varies around a mean value, the variation adding up
to a cumulative figure that is quite different from pit to pit (Figure 24).
Figure 24: Variation with depth of percentage carbon (left) and estimated actual carbon (right) in
paddock soils at the Thomas property on the Mid-North Coast of New South Wales. The
cumulative amount of carbon held to 0.5 m depth is shown on the legend. The average of the three
figures is 118.5 with a 90% confidence interval of 43%.
There are some generalities, however, and one is that the majority of the carbon
appears to be found in the first half a metre most of the time–the New England sites
being consistent in having more carbon at depth than all but a few other sites. This
cumulative carbon figure can give a good idea of the difference between plantation
and paddock soils, remembering that the amount of natural variability within each
may often mask any apparent differences (Figure 25).
Figure 25: Total soil carbon to 0.5 m depth for all sites and situations measured in northern New
South Wales as part of the Greenhouse Allies project. No variation is shown as each of these is a
singular measurement.
With the exception of the Henderson paddock measurement, the Mid-North Coast
sites appear to be a little lower than those in either of the other two regions. The
carbon at the Taylor and the two Johnston sites, with Robinson and Machin close
behind, are markedly depressed. It would be informative, perhaps, to compare this
to the growth rates of the plantation species. The effect of soil type and rainfall on
these figures is yet to be investigated, but a brief investigation of the difference
between the paddock and plantation measurements (although risky without
replicates) and age may in future prove to be a useful measure. At this stage the
results of this are anomalous, although a correction for growth rate may be useful
(Figure 26). The location of the pits could have critical bearing on these results.
Figure 26: The difference between total carbon to 0.5 m in paired plots at sites in northern New
South Wales compared with the age of the planting.
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