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The University of Tasmania (UTAS) is a public research university primarily located in Tasmania, Australia. Founded in 1890



Tasmanian organic soils  [2007]

di Folco, M;

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The character, extent and location of Tasmanian organic soils have been largelyoverlooked in Australian soil classification and taxonomy, with only a looseinterpretation of northern hemisphere organic soil classifications applied. The aim ofpresent work is to produce a classification of the organic soils, based on measurablesoil properties and to then relate the characteristic organic soil properties toenvironmental factors. The relationship between organic soil characteristics andenvironmental factors will enable predictive mapping of the occurrence and organiccontent of organic soils in Tasmania. Tasmanian organic soils were sampled across127 sites yielding a total of 1159 soil pits. Soil and environmental characteristicswere recorded for each soil pit. Unsupervised clustering of the soil characteristicsfrom each soil pit distinguished 23 organic soil groups. A classification key foridentifying the 23 clusters was produced using the soil characteristics, soil organiccarbon, humification, soil total nitrogen and organic soil depth. Dominantenvironmental factors influencing the 23 clusters were found, through vectoranalysis, smooth plate spline contouring and multinomial log-linear modelling to be:vegetation, burn frequency, topography, geology, altitude and climate. In order topredict the location and occurrence of the soils and soil characteristics producedthrough unsupervised clustering, the dominant environmental factors weresubsequently used to provid
e cluster centroids for a supervised clustering. Theresulting 41 soil groups were found to be distinguishable in terms of vegetation type,geology, topography and microtopography. The supervised clusters were found toperform better than the available vegetation classifications in predicting theunsupervised clusters. Organic soil carbon, bulk density and depth were used tomodel organic soil carbon stocks in Tasmania and provide a geographic context forthe supervised and unsupervised soil clusters. Stepwise regression of soil organiccarbon, showed slope as the dominant predictor across organic soil producingvegetation types. The regression models allowed for mapping of organic soil arealextent and soil organic carbon stocks in Tasmania, producing a value of 3,072 Tg ofsoil organic carbon over 8, 974 km2.Suggested changes to the Australian Soil Classification for the order organosolinclude 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 layersand acidity classes below pH cA 4.6. Changes to landform labels are also suggested.