Context Kandosol soils are widely distributed in Australia and are frequently used for irrigated cropping. However, under intensive irrigated cropping they can degrade due to poor structural stability where surface soil aggregates break down as a result of slaking and dispersion; the slaking is associated with low soil organic carbon levels (<1.0 g/100 g) on these frequently cultivated soils, and the dispersion is related to the moderate level of exchangeable sodium percentage (ESP) combined with low electrical conductivity (EC) levels in the soil solution. Aims To investigate the effects of applied gypsum (0, 2 and 10 t/ha), irrigation with water of low EC (0.5 dS/m) and low sodium adsorption ratio (≤2), and two tillage practices, i.e. conventional tillage (CT) and reduced tillage (RT), on the structure of a marginally sodic (ESP 6) Yellow Kandosol soil. Methods The experiment was conducted at Carnarvon, Western Australia. Key results After 2 years the soil EC (1:5) and ESP levels were significantly reduced on all plots at the three gypsum rates. The three gypsum rates also significantly affected exchangeable calcium (Ca) and magnesium (Mg) and soluble Ca and Mg levels, as well as pH and dispersion values. Micromorphological examination indicated less dispersed clay with gypsum application. Conclusions The EC results indicated that the soil will require frequent re-application of gypsum to maintain electrolyte levels and prevent dispersion. With some of the variables, RT compared to CT demonstrated greater through-flow, which was attributed to the presence of more macropores in RT. Implications A change in management from semi-arid chenopod shrublands used for grazing to intensely cultivated horticulture will require careful consideration of factors causing soil structural instability.

There is a global need for inexpensive tools for research and monitoring. Landscape function analysis (LFA) is a visual assessment procedure used to assess and monitor soil function rapidly from measurable soil surface characteristics. It uses 11 indicators of soil biogeochemical properties and processes, and generates three indices of soil function: soil stability, nutrient cycling and infiltration. These indices are strongly associated with the provision and regulation of ecosystem services such as soil retention, cycling of water and nutrients, carbon storage and biomass production. The LFA method can be used to quantify changes in soil function response to natural and anthropogenic disturbances such as variation in climate, changes in management practices and land-use change. Our research assessed LFA for monitoring soil function on livestock farms with four different strategies for grazing management and ecological restoration. With LFA, we showed that (i) soil function returned when severely eroded claypans (scalds) were rehabilitated, (ii) grazing pressure had a greater effect on soil function than grazing regime, (iii) soil function improved with a programme of planned recovery grazing, (iv) soil function increased following afforestation of grazing land with native trees of mixed species and shrubs and (v) soil function responded to seasonal effects and cropping. Our results show that LFA is an effective research and monitoring tool for farm-scale studies. The LFA method produces integrative indices for soil stability, infiltration and nutrient cycling, and provides information on soil function that can be used to guide both management decisions and soil sampling and analysis when more detailed and expensive soil research is justified.

Identifying soil with a large potential to accumulate organic carbon (OC) could maximise the mitigation benefits of carbon (C) sequestration and help prioritise resources to achieve increases in soil OC. The purpose of this laboratory incubation experiment was to determine if an upper limit to OC accumulation in soil was approached with increasing C input in basalt- and granite-derived soil. For each parent material, two soil layers were compared to observe OC accumulation in soil with a high OC concentration (0 to 0.10m, A1 horizon) and soil with a low OC concentration (0.40 to 0.50m, B2 horizon). Soil samples were incubated for up to 146days. The experiment consisted of three soil incubation cycles, with four treatments applied at the start of each cycle: soil only (control), soil and nutrients only (nutrients), high organic matter (OM) and nutrients (approximating a field equivalent of 12.4MgDM/ha; HOMN) and very high OM and nutrients (31.1MgDM/ha; VHOMN). At the beginning of cycle one 13C labelled OM was applied. There was no asymptotic behaviour between C inputs and OC accumulation in soil observed in this study. Thus, OC accumulation was not approaching an upper limit for either parent material at OM application rates ranging from field equivalents of 12.4 to 93.3MgDM/ha (equivalent to 5.4 to 40.6MgC/ha). There was no significant increase in OC concentration between cycle 2 and 3 for the VHOMN treatment in the granite-derived 0.40 to 0.50m soil. While this is not conclusive, this may indicate the soil is approaching an upper limit to OC accumulation at a lower OC concentration due to the dominance of 1:1 clays, compared to the 2:1 clay dominated basalt-derived soil. This suggests that mineralogy rather than texture may influence OC accumulation and any potential C saturation behaviour of soil. Despite increasing microbial activity, evidenced by increasing soil respiration (P<0.001) and microbial biomass C (P<0.05), as well as a significant (P<0.05) narrowing of the C:N ratio of soil, there was substantial 13C recovery (mean between 19.8 and 25.9 (1.1 se) % for both parent material) at the end of the soil incubation. This supports the hypothesis that the increases in OC accumulation were at least partly due to the conversion of plant residues into microbial detritus which is a major component of the relatively stable pool of OC in soil.

Environmental factors such as parent material and climate can have a large effect on total carbon concentration and soil carbon stocks, yet unlike vegetation type, fertiliser use and grazing pressure, these cannot be changed by management. The relative effects of these environmental and land management factors were compared in the Monaro and Boorowa regions of New South Wales (NSW), Australia. Parent material, geographic region, soil depth and soil fertility had a significant influence on soil carbon stocks to 0.70 m while pasture type (introduced vs native pastures) did not. Parent material and soil depth significantly (P < 0.05) influenced the mean soil carbon stock (Mg C/ha) in the Monaro region; 159 (11 se) in basalt-derived soils, 77 (11 se) in deep granite-derived soils and 43 (3 se) in shallow granite-derived soils. Climate also significantly (P < 0.05) influenced the mean carbon stock, with deep granite-derived soils in the Monaro region having 76.5 (11 se) compared with 51.8 (3 se) Mg C/ha in the Boorowa region. A considerable proportion of the total carbon stock to 0.70 m for all sites was measured in the subsoil (0.30 to 0.70 m). In the Monaro region, basalt-derived soil contained 43% of the total carbon stock in the subsoil, compared with 28% in deep granite and shallow granite-derived soil. In the Boorowa region, deep granite-derived soil contained 33% of the total carbon stock in the subsoil. Restricting soil carbon measurements to the surface 0.30 m of soil may result in erroneous conclusions with respect to the influence of land management on the accumulation of carbon in soil. Total carbon concentration was positively correlated with labile carbon, total nitrogen, cation exchange capacity and extractable sulfur, suggesting that for a given parent material and climate, maintaining adequate pasture nutrition may substantially increase soil carbon stocks.

This paper determines the influence of lime and gypsum on the rehabilitation of a degraded sodic soil in a semi-arid environment 12 years after application. The aim was to assess rehabilitation strategies for sodic soils as alternatives to the application of gypsum alone. An experimental site was used where lime and gypsum combinations (L0G0, lime 0 t ha–1 and gypsum 0 t ha–1; L0G1, L0G2.5, L0G5, L1G0, L2.5G0, L5G0, L1G1, L2.5G1) had been applied 12 years prior, in 1994. An earlier study had reported on the effects after 3 years of the chemical ameliorants and tillage on a range of soil physical and chemical properties at the site. The current study, sampled in 2006, assessed the effects after 12 years of lime and gypsum on soil chemistry, stability, hydraulics, vegetative growth and soil respiration. Calcium, primarily from lime, was observed to have a major effect on soil health. Significant effects on soil chemistry were limited to increases in exchangeable calcium and decreases in exchangeable magnesium, although aggregate stability in water and hydraulic conductivity were significantly improved where L5G0 was applied. Vegetation patch width, total nitrogen and carbon, and soil respiration were significantly improved where lime had been added at 2.5 or 5 t ha–1. As no lime could be detected in the soil 12 years after application, it was deduced that lime had acted as a catalyst for increased functionality in soil and vegetation interactions. This increased soil functionality resulted in an increased rate of lime dissolution in the soil.

South easterly trade winds have long been thought to transport aeolian dust across northwest Australia, but very little is known about the chemical and particle size characteristics of this material. From July 2008 to May 2009, 36 aeolian dust samples were collected monthly at four sites across Australia's northwest. The results of ion beam analysis indicate that the samples consisted of four major elemental groups, one of which appeared to be transported across the sites during months in winter and summer. This group (characterised by higher ratios of Fe, Ti and Mn/Si than the Earth's Crustal Average) also showed a decrease in particle sizes towards the west. This suggests that the dust may have had a central Australian source, while other groups richer in Si appear to have been locally derived. These results support previous models of seasonal dust transport, and may have relevance in regional climate modelling, the transport of nutrients into the Indian Ocean, mineral exploration and studies of respiratory health. (C) 2013 Elsevier B.V. All rights reserved.

The degradation of semiarid agricultural rangelands in Australia can be traced back to the 19th century when Europeans expanded into these areas. That environmental degradation remains today and continues to harm agricultural productivity. The rehabilitation of a strongly incised ephemeral stream, 'Spring Creek', in central New South Wales, as an example of what can be achieved readily by landowners, is described. The causes of environmental degradation and the main environmental factors leading to the stream erosion were identified, rehabilitation began and the behaviour of the regime for 5 years within Spring Creek and the adjacent floodplain was monitored. It was found that intrinsically unstable sub-soils and sparse ground cover due to persistent grazing by domestic livestock were the major factors leading to incision. Several physical and chemical properties were found to be the primary causes of the soil's instability.Rehabilitation focussed on stabilising the soils alongside the stream, promoting sedimentation and re-vegetation of the stream bed, with a longer-term objective of increasing the transfer of water, sediments and nutrients between the stream and its adjacent floodplain. The measures, implemented by local landowners, included the provision of in-stream porous rock weirs and the lowering of the grazing pressure on the stream bed and adjacent floodplain. Monitoring in 2007, 2009 and 2011 indicated that sedimentation was substantially faster above weirs than where there were no weirs. The rehabilitative measures resulted in the retention of fine sediment (<0.2 mm) along the stream bed behind weirs.

Carbon sequestration, reported as gains in carbon s tocks, requires measurement of carbon concentration nd bulk density of soil. Nineteen perennial pasture si t s were sampled in the Boorowa region, south-easte rn NSW to compare: i) the influence of core diameter s ize (155 mm vs 75 mm vs 40 mm) on bulk density and ii) carbon density (Mg C ha -1 to 0.30 m) calculation (fixed depth vs equivalent soil mass) on total soil carbon stock. Bulk density was significantly different ( P <0.05) with core diameter size for all soil layers to 0.30 m with the exception of the 0.05 to 0.10 m soil layer . However, due to the variability in carbon concent ration in soil there was no significant difference in carbon stocks calculated using either the fixed depth or e quivalent soil mass carbon density values regardless of core diameter size. The mean carbon stock (Mg C ha -1 to 0.30 m) calculated for the fixed depth and equivalent so il mass carbon density values using the 155 mm, 75 mm, 40 mm diameter cores was 50.9 (7.4 sd) vs 49.9 (7.3 sd) 53.8 (8.3 sd) vs 53.1 (8.2 sd), and 50.9 (8.4 sd) and 49.9 (8.0 sd), respectively. Based on these finding s, the diameter of the cores used for bulk density measurements for carbon stock calculation should be selected based on operational ease and sampling efficiency rather than notions of precision of carb on stock reporting.

The terrestrial and oceanic salt (NaCl) components in 39 dust samples from eight sites across south eastern Australia have been calculated from chemical data derived by ion beam analysis (IBA). For samples identified as having a positive terrestrial salt ratio (TSR; i.e., the abundance of terrestrial salt relative to total salt expressed as a percentage), back trajectory analysis (estimation of the path of the wind affecting the site) was used to verify the likelihood of a terrestrial source for such salt. This procedure indicated that the terrestrial salt input to south eastern Australia is non-negligible compared to that of sea salt and the most likely sources of the terrestrial salt deposited in such area are the inland saline regions of the Lake Eyre and Murray Darling Basins. Terrestrial salt ratio values readily screen out the majority of samples for which a terrestrial salt component is unlikely. Thus, calculating the ratios to identify samples which are potentially influenced by terrestrial salt (e.g., prior to conducting a back trajectory analysis on such samples) appears to be useful, especially since such determinations can be done with small sample sets for which statistical analysis is not appropriate. (C) 2011 Elsevier B.V. All rights reserved.

Soil salinity (high levels of water-soluble salt) and sodicity (high levels of exchangeable sodium), called collectively salt-affected soils, affect approximately 932 million ha of land globally. Saline and sodic landscapes are subjected to modified hydrologic processes which can impact upon soil chemistry, carbon and nutrient cycling, and organic matter decomposition. The soil organic carbon (SOC) pool is the largest terrestrial carbon pool, with the level of SOC an important measure of a soil's health. Because the SOC pool is dependent on inputs from vegetation, the effects of salinity and sodicity on plant health adversely impacts upon SOC stocks in salt-affected areas, generally leading to less SOC. Saline and sodic soils are subjected to a number of opposing processes which affect the soil microbial biomass and microbial activity, changing CO(2) fluxes and the nature and delivery of nutrients to vegetation. Sodic soils compound SOC loss by increasing dispersion of aggregates, which increases SOC mineralisation, and increasing bulk density which restricts access to substrate for mineralisation. Saline conditions can increase the decomposability of soil organic matter but also restrict access to substrates due to flocculation of aggregates as a result of high concentrations of soluble salts. Saline and sodic soils usually contain carbonates, which complicates the carbon (C) dynamics. This paper reviews soil processes that commonly occur in saline and sodic soils, and their effect on C stocks and fluxes to identify the key issues involved in the decomposition of soil organic matter and soil aggregation processes which need to be addressed to fully understand C dynamics in salt-affected soils.

This paper investigates index models as a tool to estimate the risk of N and P source strengths and loss at the catchment scale. The index models assist managers in improving the focus of remediation actions that reduce nutrient delivery to waterbodies. N and P source risk factors (e.g. soil nutrient concentrations) and transport risk factors (e.g. distance-to-streams) are used to determine the overall risk of nutrient loss for a case study in the Tuross River catchment of coastal southeast Australia. In the development of the N index model for Tuross, particulate N was considered important based on the observed event water quality data. In contrast to previous N index models, erosion and contributing distance were therefore included in the Tuross River catchment N index. Event-based water quality monitoring, and soil information, or in data-poor catchments conceptual understanding, are essential to represent catchment-scale processes. The techniques have high applicability in other catchments, and are complementary to other modelling techniques such as process-based semi-distributed modelling. Index models generally provide much more detailed spatial resolution than fully- or semi-distributed conceptual modelling approaches. Semi-distributed models can be used to quantify nutrient loads and provide overall direction to set the broad focus of management. Index models can then be used to refine on-the-ground investigations and investment priorities. In this way semi-distributed models can be combined with index models to provide a set of powerful tools to influence management decisions and outcomes.

Eolian dust plays a significant role in landscape development and landscape processes in Australia. Thin dust mantles, rarely exceeding 3m in thickness, have been identified across many parts of the Australian landscape, particularly in southeastern Australia. The nature and properties of these dust materials can have a major influence on environmental degradation processes such as salinisation and soil erosion. Despite the existing body of research regarding this topic, there are still conflicting views about the likely sources, transport modes and properties of eolian dust in the Australian landscape. The aim of this review is to synthesise much of the available information and put forward a working hypothesis for the distribution and fundamental properties of dust deposits in southeastern Australia. A conceptual model describing the various dust sources and sinks, and the modes of transport of dust materials both into and out of these source areas, is introduced. The model identifies key source areas, such as the alluvial and lacustrine environments of the Lake Eyre and Murray-Darling Basins, and sinks, such as the Eastern Highlands. Transport rates and paths for eolian-dust materials across the Australian continent are also outlined. The model places particular emphasis on the recycling of dust, whereby sediments sourced from the Eastern Highlands are transported westward via the major alluvial networks, and deposited on floodplains or in terminal drainage systems. These sediments are then available to be reworked into local eolian landforms prior to re-entrainment of the finer materials in the easterly dust pathway. The characteristics of deposited eolian sediments are then outlined in detail, focusing particularly on their particle-size distribution, mineralogical composition, and geophysical and geochemical properties. The review also presents data and images of dust materials sampled from source areas, sink areas, as well as materials that have been deposited by modern dust events. Finally, the role of dust materials in land-degradation processes, particularly soil erosion, is discussed. The degree of reworking of the eolian sediments, the extent of leaching and the level of sodicity are all important in determining soil structural stability and hence erosion potential of these materials.

Understanding fluid flow, displacement, and mixing processes in natural porous media is fundamentally dependent upon the accurate characterisation of complex 3-dimensional structures. This current study delineated the distribution of conducting regions within a suite of regolith materials as they interacted with electrolyte solutions of different concentrations. Previous studies on the effects of electrolyte concentration on clay swelling and dispersion and the concomitant changes in pore structure, and hence soil permeability, have mainly been carried out on repacked samples of disturbed surface soils. This study used unconsolidated materials recovered as undisturbed cores from a saline aquifer from the deeper regolith (8.0–55.8 m). Progressive dilution of the electrolyte concentration of the percolating fluid (while maintaining a constant sodium adsorption ratio) was used to alter the pore structure of these saturated regolith materials. The electrolyte concentration was reduced from an initial value of 383 m.e./L (the original electrolyte concentration of the saline aquifer) to below the threshold concentration, and finally the cores were rinsed with deionised water. The corresponding changes to the regions conducting fluid and therefore pore structure, and the major fluid pathways followed during the percolation process, were imaged using gamma emission computed tomography. Five experimental core samples from depths of 8, 28, 30 (×2), and 55 m were used in the experiments. The average hydraulic conductivity was measured and found to decrease as a function of electrolyte concentration. The regions containing the major fluid pathways were found to decrease in volume as a function of electrolyte concentration. Clay mineralogy, sodium adsorption ratio, and grain size characteristics were found to be positively correlated with reductions in the average hydraulic conductivity. This method has the potential to aid in our understanding of the fundamental processes that govern the dynamics of pore structure changes and hence fluid flow in porous regolith materials, particularly in relation to changes in the electrolyte concentration and sodium adsorption ratio of the pore fluid. Such data will add significantly to our understanding of factors that affect the hydraulic properties of regolith materials under saline/sodic conditions.