Comparison of structural stability, carbon fractions and chemistry of krasnozem soils from adjacent forest and pasture areas in south-western Victoria
- Authors: Carter, Martin , Skjemstad, J. O. , MacEwan, Richard
- Date: 2002
- Type: Text , Journal article
- Relation: Australian Journal of Soil Research Vol. 40, no. 2 (2002), p. 283-298
- Full Text: false
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- Description: Basalt-derived krasnozems are generally well-structured soils; however, there is a concern that intensive agricultural practices may result in an adverse decline in soil organic carbon, organic matter chemistry, and structural quality over time. A study was conducted on loam to silty clay loam krasnozems (Ferrosols) near Ballarat in south-western Victoria to assess changes in soil C, soil structural stability, and C chemistry, at the 0-10 cm soil depth, under 3 paired sites consisting of adjacent long-term forest (Monterey pine or eucalyptus) v. 30 year cropping [3 year pasture-2 year crops (potato and a root crop or grain)]. Soil structural stability was also characterised in the A and B horizons under long-term eucalyptus and several cropped sites. Organic C levels in the A horizons for all the soils were relatively high, ranging from 46 to 89 g/kg. A lower organic C (30%), associated mainly with loss of the sand-sized (> 53 mum) macro-C fraction, and a decrease in exchangeable Ca and Mg was found in the agricultural soils, compared with forest soils. Physically protected C in the <53 μm fraction, as indicated by UV photo-oxidation, was similar among soils. Wet sieving indicated a decline of both C and N concentration in water-stable aggregates and the degree of macro-aggregation under agricultural soils, compared with the forest soils. However, soil structural changes under cropping were mainly related to a decline in the >5 mm sized aggregates, with no deleterious increase in the proportion of 0.10 mm aggregates. Solid state C-13 NMR spectroscopy indicated a decrease in O-alkyl and alkyl C under pasture and cropping compared with forest soils, which was in agreement with the decline in the macro-C fraction. Characterisation of C chemistry following UV photo-oxidation showed that charcoal C (dominant presence of aryl C) accounted for 30% of the total soil organic C, while other functional groups (polysaccharides and alkyl C) were probably protected within micro-aggregates. Based on soil organic C and aggregate stability determinations alone, the implications for soil physical quality, soil loss, and diffuse pollution appear minimal.
Salinity on the southeastern Dundas Tableland, Victoria
- Authors: Dahlhaus, Peter , MacEwan, Richard , Nathan, Erica , Morand, Vincent J
- Date: 2000
- Type: Journal article
- Relation: Australian Journal of Earth Sciences Vol. 47, no. 1 (2000), p. 3-11
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- Description: Historical evidence of early salinity, vegetation and landuse changes, and pedological studies have been used in formulating a new model for salinity processes acting on the Dundas Tableland in southwestern Victoria. Contrary to previous assumptions, salinity in this area was a feature of the pre-European landscape and was noted in the earliest surveys and journals. Analysis of historical records show an initial post-settlement increase in the tree numbers, followed by a rapid decline much later than previously assumed. Accumulation of salts in the regolith may be attributed to marine incursions during the Miocene and Pliocene, the extensive weathering to develop a deep regolith, and wind-blown and cyclic salt accumulation. A trend analysis of historical streamflow and bore hydrograph records does not indicate rising groundwater levels. The pedological features of duplex and sodic soil profiles support a history of prolonged seasonal waterlogging. A model with seasonal lateral flow of water through the upper regolith can better account for the spread of salinity than the rising groundwater hypothesis. By control of waterlogging, land managers could improve soil structure, enhance root growth and soil water use, as well as inhibit the spread of salinity.
Hydropedology, geomorphology and groundwater processes hold the keys to land degradation - case studies in SW Victoria, Australia
- Authors: MacEwan, Richard , Dahlhaus, Peter , Fawcett, Jonathon
- Date: 2006
- Type: Text , Conference paper
- Relation: Paper presented at 18th World Congress of Soil Science, Philadelphia, Pennsylvania, USA : 9th-15th July 2006
- Full Text: false
- Description: Soil is the component in the landscape along with land use management and vegetation that determines all the partitioning of water balance components that affect surface hydrology (runoff to waterways and wetlands) and recharge to groundwater. Most soil and land degradation processes are hydrologically driven or depend on hydrological conditions. Conceptual models and quantification of erosion processes (wind erosion is a result of lack of moisture), land salinisation, acidification, nutrient loss and impacts of nutrient movement, all require an understanding of the role of hydrology specific to the landscape under consideration. In Australia, salinity is a major problem for agriculture in irrigated and rainfed (‘dryland agriculture) land and has significant economic impacts in urban areas too. A general water balance approach has been used to conceptualise the processes and the problem. Large scale clearing of treed landscapes in favour of annual crops and pastures has been seen as the major change in the water balance of Australian landscapes since settlement. This change in vegetation and water use is frequently cited as the most significant factor in causing land salinisation, which is attributed to increase in groundwater recharge, mobilisation of salts, groundwater rise and discharge. We provide three case studies for landscapes that require quite different conceptual models and all of which are in some degree counter to the developed conventional wisdom regarding increased salinity. These case studies illustrate the importance of developing an appropriate conceptual model of hydrological processes in the ‘critical zone', in particular for implementation of policy and practice in land management. Case 1. South Eastern Dundas Tablelands, Victoria. In this landscape the apparent degradation of land by salinity is the result of changed hydrological conditions but has not resulted from increased groundwater discharge or increased salt accumulation. We have evidence that groundwater recharge and discharge have not increased since clearing of the landscape during European settlement. Laboratory hydrological studies in large diameter cores from soil and regolith, interpretation of redoximorphic features and functional horizons in the field and analysis of historical records of streamflow support this hypothesis. We also show that the degradation of salt affected areas is due to fluctuating waterlogging and drying of the soil causing cyclic redox conditions and changes in soil chemistry. Case 2. Dissected Coastal Plain, Victoria. In this landscape, slowly permeable marine clay overlain by coastal sand deposits provides a classic ‘layer cake' picture of differentially permeable material. The unconsolidated nature of the clays and the relatively deep dissection that exists presents a landslide prone landscape and one that also shows the effects of salting in low areas. In this region we show that upward pressure from a deep (200 m) confined freshwater aquifer maintains saturation in the marine clay and that waterlogging, landslides and salinity result from hydrological dynamics of the upper few metres of regolith and soil. Evidence has been collected from field survey, groundwater studies, geotechnical measurements and regolith mineralogy. Case 3. Granite Uplands, Victoria. In this landscape we have interpreted redoximorphic features of functional horizons and measurement of shallow groundwater salinities in a toposequence. Our conceptual model is of a regional saline groundwater system discharging in springs relatively high in the landscape. We show the role of shallow throughflow of water in the soil in spreading salt from these point sources, simultaneously diluting the effect of salinity in local drainage lines but increasing the area of salt affected land upslope from the drainage lines. In each case study area we have been compelled to develop an understanding that fits the landscape realities. We have used empirical observations and interpretation of soil morphology, regolith and groundwater characteristics, laboratory studies, soil chemistry and hydro-chemistry to support our work. We stress the importance of this approach integrating the sciences of hydrology, pedology, chemistry and geology in coming to appropriate conclusions about land degradation processes, especially if we are to advise on land management investment and policy to tackle degradation.
- Description: 2003002070
Hydropedology, Geomorphology, and Groundwater Processes in Land Degradation: Case Studies in South West Victoria, Australia
- Authors: MacEwan, Richard , Dahlhaus, Peter , Fawcett, Jonathon
- Date: 2012
- Type: Text , Book chapter
- Relation: Hydropedology p. 449-481
- Full Text: false
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Multi-source data integration and identification of uncertainties affecting production of a digital soil map
- Authors: Robinson, Nathan , Benke, Kurt , Hopley, J. , MacEwan, Richard , Clark, R. , Rees, David , Kitching, Matt , Imhof, Mark , Bardos, David
- Date: 2014
- Type: Text , Conference paper
- Relation: GlobalSoilMap: Basis of the Global Spatial Soil Information System - Proceedings of the 1st GlobalSoilMap Conference p. 353-358
- Full Text: false
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- Description: Production of a digital soil map for the state of Victoria in Australia is subject to various errors arising from the use of legacy data (as is often the case around the globe). Potential sources of uncertainty for inputs and methods undertaken in the creation of a Victorian DSM version 1.0 (VicDSMv1) are identified. These sources of uncertainty are recognised and issues discussed including their potential contribution to error propagation. Examples include possible errors associated with legacy soil maps, soil sites, laboratory analysis and predictive modelling by regression or spline approaches. Experiences in processing of legacy data in Victoria are described and some aspects of incorporating uncertainty in data discussed. As part of this initial DSM exercise these uncertainties and contextual information will be captured as associated metadata. A framework, as a five component process model for integrated assessment of uncertainty, is suggested based on uncertainty in the mapping process. © 2014 Taylor & Francis Group, London, UK.
Soil data for biophysical models in Victoria, Australia : Current needs and future challenges
- Authors: Robinson, Nathan , Dahlhaus, Peter , MacEwan, Richard , Alexander, J. K.
- Date: 2016
- Type: Text , Journal article
- Relation: Geoderma Regional Vol. 7, no. 3 (2016), p. 259-270
- Full Text: false
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- Description: The use of biophysical models to support increased food production and environmental protection is on the rise. This paper reviews the demand for, and trends in, soil property data for various biophysical models being used in Victoria, Australia, over the 2009-2014 period. The study used surveys, workshops and interviews with public sector modellers to examine perceptions of the soil parameters that affect model sensitivity and error. Although the data requirements of models have remained similar over the 5 year period, the diversity of models used has decreased. There is evidence of increased application of models at point/site scale to support grains, dairy and livestock production industries in Victoria. Opportunities are identified to deliver finer scale soil data from digital soil mapping to better meet modelling requirements for agricultural industries in Victorian landscapes. © 2016 Elsevier B.V. All rights reserved.