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a recently-active volcano in Papua New Guinea (Bleeker and Sageman‚ 1990). The site
receives ca. 3500 mm of rainfall annually and currently supports a cover of coconuts
( Cocos nucifera ) and cocoa ( Theobroma cacao ). The C:N ratios suggest ready decom-
posability (Chapter IV.1.3.3). However‚ the mineralogy of the soil is dominated by ver-
miculite‚ volcanic glass‚ allophane and imogolite which implies that some protection
of the organic matter may occur (see Chapter IV. 1.3.2). Figure I.33e presents data from
a poorly-drained acid histosol supporting a forest cover of Southern Beech ( Nothofagus
spp.) and podocarps ( Podocarpus spp.) located on the humid (2020 mm annual rainfall)
western coast of South Island New Zealand at ca. 42°S (Mew and Lee‚ 1981). The thick
(44 cm) peat O horizons (depths conventionally indicated by negative numbers) are
underlain by loess and alluvium (largely greywacke and granite). Carbon contents in
the upper peat horizons are equivalent to those of fresh plant material but diminish
with increasing depth and undergo an abrupt reduction at the transition with the pre-
dominantly-mineral horizons. Appreciable carbon still occurs in the upper gleyed
mineral horizons and diminishes with depth in the solum‚ apart from a slight increase
in the upper B horizon. C:N ratios (see below) are typically high‚ up to more than 80
in the O horizon and greater than 53 in all mineral horizons. Figure I.33f presents
the depth distribution of carbon concentrations in a vertisol from warm temperate east-
ern Australia (Ross‚ 1986). This soil developed on alluvial‚ slightly-calcareous parent
materials beneath an open forest vegetation of Acacias with perennial grasses. Ratios are
typical of other Australian vertisols and vary little with depth.
Close associations of carbon with nitrogen‚ sulphur‚ phosphorus and other nutrient
elements occur in dead plant and animal tissues. As discussed later in this topic these
tissues must generally be broken down by the soil biota to allow their contained nutrient
elements to be recycled.
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