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Tasmanian organic soils


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di Folco, M 2007 , 'Tasmanian organic soils', PhD thesis, University of Tasmania.

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The character, extent and location of Tasmanian organic soils have been largely
overlooked in Australian soil classification and taxonomy, with only a loose
interpretation of northern hemisphere organic soil classifications applied. The aim of
present work is to produce a classification of the organic soils, based on measurable
soil properties and to then relate the characteristic organic soil properties to
environmental factors. The relationship between organic soil characteristics and
environmental factors will enable predictive mapping of the occurrence and organic
content of organic soils in Tasmania. Tasmanian organic soils were sampled across
127 sites yielding a total of 1159 soil pits. Soil and environmental characteristics
were recorded for each soil pit. Unsupervised clustering of the soil characteristics
from each soil pit distinguished 23 organic soil groups. A classification key for
identifying the 23 clusters was produced using the soil characteristics, soil organic
carbon, humification, soil total nitrogen and organic soil depth. Dominant
environmental factors influencing the 23 clusters were found, through vector
analysis, smooth plate spline contouring and multinomial log-linear modelling to be:
vegetation, burn frequency, topography, geology, altitude and climate. In order to
predict the location and occurrence of the soils and soil characteristics produced
through unsupervised clustering, the dominant environmental factors were
subsequently used to provide cluster centroids for a supervised clustering. The
resulting 41 soil groups were found to be distinguishable in terms of vegetation type,
geology, topography and microtopography. The supervised clusters were found to
perform better than the available vegetation classifications in predicting the
unsupervised clusters. Organic soil carbon, bulk density and depth were used to
model organic soil carbon stocks in Tasmania and provide a geographic context for
the supervised and unsupervised soil clusters. Stepwise regression of soil organic
carbon, showed slope as the dominant predictor across organic soil producing
vegetation types. The regression models allowed for mapping of organic soil areal
extent and soil organic carbon stocks in Tasmania, producing a value of 3,072 Tg of
soil organic carbon over 8, 974 km2.
Suggested changes to the Australian Soil Classification for the order organosol
include the addition of folic, lignic, arenic and argyllic to the differentiae. Suggested family criteria include: humification of surface tiers, organic horizon thickness,
botanical composition of surface layers, botanical composition of dominant layers
and acidity classes below pH cA 4.6. Changes to landform labels are also suggested.

Item Type: Thesis - PhD
Authors/Creators:di Folco, M
Copyright Information:

Copyright 2007 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

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