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Tropical pasture legumes such as Desmanthus are expected to improve pasture productivity in the extensive grazing systems of Northern Australia. However, the soils in these areas are often hostile (e.g., hard-setting and nutrient-deficient), which reduces legume emergence and establishment. Furthermore, these soils are often not ameliorated with amendments such as gypsum or starter fertilisers before planting. A pot trial was conducted to investigate differences in the emergence and early growth of four Desmanthus species. The legumes were grown in three alkaline clay soils that were unamended or amended with either gypsum (1 t CaSO4.2H2O ha−1 equivalent), a starter MAP fertiliser (12 kg P ha−1 equivalent), or both gypsum and the starter fertiliser. Seedling emergence was recorded daily and shoot yield was determined after six weeks' growth. Final seedling emergence (as a percentage of viable seeds) varied among the Desmanthus species (c.f. D. leptophyllus = 63%, D. pernambucanus = 68%, D. bicornutus = 85%, and D. virgatus = 86%). On average, across the treatments, gypsum increased seedling emergence by 15%, whereas the starter fertiliser had no effect. The shoot yields and shoot phosphorus content of the Desmanthus species generally increased in response to the starter fertiliser. The collective results demonstrated that there were differences in emergence and early growth among the four Desmanthus species, which indicates that Desmanthus cultivar selection may be important in the relatively hostile soils of Northern Australia. Gypsum was an effective amendment for seedling emergence, whereas the starter fertiliser was an effective amendment to increase legume productivity. [ABSTRACT FROM AUTHOR]

Digital soil mapping provides estimates of soil properties and, in turn, an understanding of the spatial variation in soil across landscapes. In recent years, several digital soil mapping products have been released across the world. An end user in New South Wales (NSW), Australia, could choose between a global product (SoilGrids), a national product (Soil and Landscape Grid of Australia) and a state product (NSW digital soil maps). All predict at grid resolutions of 250 m or less, which approaches the required detail for within‐field site‐specific management such as variable‐rate application of agricultural inputs. In this study, the quality of clay and soil organic carbon (SOC) products (0–30 cm) from these three publicly available digital soil maps (DSM) were validated with an external dataset of 394 soil observations, collected from 14 farms across eastern Australia. Each farm was sampled using stratified random sampling, allowing for unbiased estimates of prediction quality at three spatial supports: point (soil core), strata (management zone) and farm. For the clay attribute, this study observed Lin's concordance correlation coefficient (LCCC) values of 0.22–0.37 at the point spatial support, far below reported values. This improved at the strata spatial support with LCCC values of 0.20–0.60 and the farm spatial support with values of 0.07–0.54. For SOC, LCCC values ranged from 0.25 to 0.45 for points, 0.31–0.55 for strata and 0.31–0.60 for farms. The grid resolution of DSMs depends largely on the resolution of the covariates used, and current efforts look to incorporate more recent, finer resolution covariates to create higher‐resolution soil maps. However, the results of this study suggest that both the grid resolution and spatial support used in DSMs need further consideration. Rather than letting the resolution of covariates determine the resolution of DSMs, this should also be determined by the number of soil observations available for modelling, their distribution in geographic and attribute space and the prediction quality. Highlights: DSM products do not meet published accuracies when assessed with an independent datasetThe large‐extent DSM products were unable to represent within‐farm variabilityAggregation of the DSM products over large spatial supports improved accuraciesDSM products should be created at different spatial supports, each with an associated uncertainty [ABSTRACT FROM AUTHOR]

There is a global imperative to satisfy the demand for grain production and minimize environmental impacts associated with applying nitrogen (N) fertilizers. Soil is critical to the regulation of N supply and loss from agricultural systems. We summarize field-based measurements of these pathways for Australian dryland (rainfed) grain cropping soils in three agroclimatic cropping regions. In situ net N mineralization rates have been widely reported from Australian dryland cropping soils, with up to 285 kg N ha-1 mineralizing during the growing season and up to 190 kg N ha-1 accumulating during the fallow between harvest and sowing of the next crop. Ammonia volatilization measurements are sparse and cover few Australian dryland cropping soils, with field-measured losses ranging from 0% to 34% of applied N. Nitrous oxide emissions have been quantified for all key Australian grain growing regions and the median annual rate is low (0.19 kg N ha-1 yr-1). Dinitrogen losses via denitrification are poorly understood with evidence that they may be substantial (> 50% of N fertilizer applied) from soils high in clay or organic carbon. Our understanding of nitrate leaching losses comes largely from coarse-textured, free-draining soils that have not received N fertilizer. Long-term studies investigating all key soil N supply and loss pathways and using a combination of field-based measurements, laboratory-based process studies, and modeling are required to advance our understanding of soil N supply and losses from contemporary and future dryland cropping systems in Australia. [ABSTRACT FROM AUTHOR]

Eucalyptus pellita and Acacia mangium are widely planted in the tropics and managed over five-to-fifteen-year rotations for wood and wood products. This study compares the growth of routine plantings of A. mangium with trial plantings of E. pellita and nearby native forests across six broadly distributed locations on Melville Island, northern Australia. In addition to tree growth measurements, litter mass and chemical properties, and topsoil (0–10 cm) physical and chemical parameters were assessed. Melville Island has a pronounced seasonal rainfall and soils that range from loamy sand to sandy loam textures; across the sites sampled soils comprised 65–85% sand and 8–16% clay. Across our sites, the maximum mean annual increment of E. pellita was 31.12 m3/ha/year compared to 14.64 m3/ha/year for A. mangium , with stand volume strongly positively correlated with clay content. On a site basis tree volume growth correlated strongly with soil clay content, with lower survival on sites with less clay in the predominantly sandy soils. The higher E. pellita growth compared with A. mangium reduced available phosphorous and calcium in topsoil, indicating that addition of P and Ca in subsequent rotations will be important to maintain and increase E. pellita productivity. The N 2 -fixing species, A. mangium , significantly increased nitrogen in litter (1.88 ± 0.04%) and in top soil (0.15 ± 0.01%) compared to E. pellita (litter 0.93 ± 0.05%; topsoil 0.11 ± 0.01%) so that carbon to nitrogen (C/N) ratios in Acacia litter (23.90 ± 0.81) and soil (23.06 ± 0.91) were significantly lower than in Eucalyptus (litter 46.30 ± 2.66; top soil 27.66 ± 1.65). Topsoil C/N also decreased with increasing soil clay content in all land uses (A. mangium, E. pellita, native forests) indicating better conditions for decomposer activity and turnover in sites with higher clay content soils. The Eucalyptus plantation drawdown of N and PO 4 3- in topsoil suggests that future plantings of E. pellita may benefit from additional N fixed into biomass and soil organic matter by the preceding A. mangium plantations. Tree growth correlations with rainfall and soil characteristics showed growth is best explained by annual rainfall, soil texture (as a percentage of clay or of sand), soil electrical conductivity, and soil bulk density. Overall, in tropical long dry season regions, for plantation development on sandy soils, E. pellita is a better choice than A. mangium. • Eucalyptus pellita had higher productivity than Acacia mangium. • While A. mangium increased soil N, E. pellita tended to decline soil N status. • E. pellita was more efficient at taking up soil available P and Ca. • E. pellita growth is influenced by rainfall, bulk density, and sand content. • Stocking rate should be higher in clayey sites with higher water availability. [ABSTRACT FROM AUTHOR]

Questions: Woody species are crucial biotic components in many of Earth's terrestrial ecosystems because they support multiple ecosystem functions. The occurrence of woody species (i.e. their likelihood of being present at a single position) is driven by both climate and soil properties. However, empirical evidence is lacking on how multiple environmental factors regulate woody species occurrence across various climate regimes, limiting our ability to predict woody species distribution under different climate change scenarios. Location: Woody plant species in eastern Australia; 1,500 km gradient. Methods: We surveyed 6,353 mature (height >4 m) woody plants from 62 woody species at 150 sites along a 1,500 km climatic (i.e. aridity) gradient in eastern Australia, and used a generalized linear mixed model to explore the impact of summer rainfall, available soil phosphorus in the surface layer (0–10 cm), subsurface (100–200 cm) soil moisture and clay content, and interactions between aridity and the three soil variables on woody species occurrence (presence/absence). Results: The overall occurrence of Australian woody species declined as the concentration of available soil phosphorus in the surface layer increased, with the impacts varying with increasing aridity. Subsurface soil moisture had strong positive effects on woody species occurrence in mesic areas, but the effect was attenuated with increasing aridity. Subsurface soil clay regulated the distribution of woody species, with finer soils promoting the likelihood of species occurrence in the dry subhumid zone, whereas coarser soils supported more woody species in the arid zone. Conclusions: Our study provides empirical evidence that the distribution of Australian woody species is regulated by large‐scale shifts in soil moisture and available soil phosphorus, and local‐scale heterogeneity in soil texture. Our results suggest that forecasted climate change may restrict the distribution of woody species preferring particular soils, but expand the range of woody species that occur on dry or infertile soils. [ABSTRACT FROM AUTHOR]

Aim: In Australia, natural grasslands largely occur on fertile clay soils and have consequently been extensively cultivated since European settlement. Other studies have demonstrated that passive restoration of subtropical grassland is possible in environments where there is substantial native remnant vegetation in the surrounding landscape. This study examined a chronosequence of abandoned fields to investigate the recovery of fragmented grassland in a matrix of cultivated land with significant exotic species that may impede succession. Location: Darling Downs, Queensland, Australia. Methods: In this study we surveyed a chronosequence of ex‐cultivated subtropical grasslands in Queensland's Darling Downs, where only 1% of the original grasslands remain. Floristic surveys were carried out in 80 fallow sites up to 51 years old, and data were compared with 16 previously surveyed remnant grasslands on the same land type. Results: Richness of native species increased with time since cultivation and approached, but did not reach, that of remnant grasslands after 51 years, whereas the richness of exotics declined with time since cultivation. Rainfall and grazing positively and negatively affected exotic plant abundance respectively and these factors had no significant direct or indirect effect on the native species richness. In terms of composition, fallow grasslands supported 54% of the native plant species from remnant grasslands after 51 years. The native perennial grasses Dichanthium sericeum and Aristida leptopoda were the only dominant species in the remnants that were present in more than 60% of the fallow grasslands. Of the species from remnants that were "missing" from fallow sites, most were native perennial forbs and grasses. Compositional dissimilarity of fallow grassland to remnant grasslands remained high after 51 years (78%). Grassland species that are uncommon in nearby hill woodlands were preferentially absent in fallow grassland and this partly explains the slow compositional recovery. Conclusion: In a highly fragmented landscape, passive restoration is only partially effective. The restoration of grassland is probably enhanced by repositories of native seeds from hill woodlands that are too rocky to cultivate. However, some species may have to be actively reintroduced to achieve complete recovery. In this landscape, where grazing is a dominant land use, exotic species do not seem to impede succession. [ABSTRACT FROM AUTHOR]

Accelerating sea-level rise poses a threat to mangroves and salt marshes. Sediment accretion on the soil surface and belowground root production is proposed to increase soil elevation enabling these intertidal habitats to maintain their position relative to mean sea level. However, shallow soil subsidence is frequently observed, which may cancel out or even outweigh the positive effects of surface accretion and root production on soil elevation gains. The processes that lead to shallow soil subsidence have not often been investigated. Here, we used computed tomography (CT) imaging to determine the volume of coarse pores in the top 20 cm of 30-cm-deep soil cores collected from mangroves and salt marshes within Moreton Bay, eastern Australia. The four field sites have long-term observations of variation in soil surface elevation gain, surface accretion rate, and shallow subsidence rate using the rod surface elevation table-marker horizon (RSET-MH) method. Over our sites, we found that the rates of shallow soil subsidence were positively related to the volume of soil coarse pores and soil clay and silt content rather than to the volume of fine pores or total porosity or other soil properties. In turn, the volume of soil coarse pores was positively related to the volume of animal burrows and root mass. Fine-pore volume and total porosity of soils were negatively associated with soil bulk density, which was in turn negatively related to soil organic matter content. Our results indicate influences of differently sized soil pores in shallow soil subsidence and suggest that animal burrowing may play a role in shallow soil subsidence. [ABSTRACT FROM AUTHOR]

Aim: Understanding past distributions of people across the landscape is key to understanding how people used, affected and related to the natural environment. Here, we use habitat suitability modelling to represent the landscape distribution of Tasmanian Aboriginal archaeological sites and assess the implications for patterns of past human activity. Location: Tasmania, Australia. Methods: We developed a RandomForest 'habitat suitability' model of site records in the Tasmanian Aboriginal Heritage Register. We applied a best‐effort bias correction, considered 31 predictor variables relating to climate, topography and resource proximity, and used a variable selection procedure to optimize the final model. Model uncertainty was assessed via bootstrapping and we ran an analogous MaxEnt model as a cross‐validation exercise. Results: The results from the RandomForest and MaxEnt models are highly congruent. The strongest environmental predictors of site occurrence include distance to coast, elevation, soil clay content, topographic roughness and distance to inland water. The highest habitat suitability scores are distributed across a wide range of environments in central, northern and eastern Tasmania, including coastal areas, inland water body margins and forests and savannas in the drier parts of Tasmania. With the exception of coastal areas much of western Tasmania has low habitat suitability scores, consistent with theories of low‐density Holocene Tasmanian Aboriginal settlement in this region. Main conclusions: Our modelling suggests Tasmanian Aboriginal people occupied a heterogeneity of habitats but targeted coastal areas around the whole island, and drier, less steep and/or open forest and savanna environments in the central lowlands. The western interior was identified as being rarely used by Aboriginal people in the Holocene, with the exception of isolated pockets of habitat; yet whether this is a true reflection of Aboriginal‐resourceuse demands increased archaeological surveys, particularly in the Tasmanian Wilderness World Heritage Area. [ABSTRACT FROM AUTHOR]

There is newly invigorated interest in intensifying agriculture in northern Australia, and research has identified up to 17 M ha of suitable soils, much of which are floodplains. Given that 88% of these best soils for agriculture occur outside the current protected area network, and floodplains are a minority habitat in northern Australia, developing northern Australia whilst maintaining its biodiversity will be a great challenge. Ants are a particularly prominent and diverse faunal group within northern Australia, but almost nothing is known of the floodplain fauna. We sampled 20 pairs of plots in floodplains and surrounding savannas in three locations in the high rainfall zone of the Northern Territory to investigate the ant faunal composition of the floodplains, to determine to what extent they are comprised of species unique to floodplains or just a subset of the broader savanna fauna. We collected 114 species from 29 genera. Eighteen species were found only in floodplain plots, but only three were definitively floodplain specialists and another four had a propensity for clay soils. For all locations combined, savanna plots contained approximately 1.7 times more species than floodplain plots. Multivariate analysis found that the two habitats supported distinct ant faunas and the three locations also had distinct faunas. Nine species in this study were new to science, suggesting that there are many other species yet to be discovered. The results indicate that floodplains have conservation value for ant biodiversity, as is the case for other components of the biota. Efforts to intensify agriculture on north Australian floodplains therefore need to have effective conservation considerations if we are to achieve ecologically sustainable development. [ABSTRACT FROM AUTHOR]

Priming of soil organic carbon (SOC) is a crucial factor in ecosystem carbon balance. Despite its increasing importance in the changing global climate, the extent of influence of temperature and soil properties on the priming effect remains unclear. Here, soil priming was investigated using 13C labeled wheat residues in two cultivated, subtropical (Vertisol) and semi-arid (Luvisol), soils of Australia at four incubation temperatures (13, 23, 33 and 43 °C). The priming effect was computed from respired CO 2 and associated δ13C, which were measured periodically over the 52-day incubation period. Wheat residue addition resulted in greater priming effect in the Luvisol (1.17 to 2.37% of SOC) than the Vertisol (0.02 to 1.56% of SOC). The priming of SOC was the highest at 23 °C in the Luvisol, and at 43 °C in the Vertsiol, which indicates a variable positive priming effect of temperature in different soil types. Wheat residue addition significantly increased the temperature sensitivity (Q 10) of SOC mineralization in the Vertisol at temperature ranges below 33 °C (i.e., 13–23 and 23–33 °C) and had no significant effect in the Luvisol. A negative correlation was observed between temperature and the Q 10 values. Across soils, the Q 10 of residue C was lower than SOC suggesting that soil C is more vulnerable to climatic warming. This work demonstrates that the magnitude of SOC priming by wheat residue and Q 10 of SOC mineralization varied significantly with soil type (Luvsiol > Vertisol) and incubation conditions (temperature and time). Given the current trend towards increasing atmospheric temperatures, future studies should evaluate temperature effects on the priming of different pools of SOC induced by crop residue in different agro-ecosystems. • The wheat residue addition caused greater SOC priming in the sandy clay loam than clayey soil. • Temperature significantly influenced SOC priming but this differed by soil type. • The difference in SOC priming between sandy clay loam and clayey soil was greater at ≤23 °C temperatures. • Wheat residue significantly increased the Q 10 of SOC mineralization but only in clayey soil below 33 °C. [ABSTRACT FROM AUTHOR]

Abstract Chickpea is susceptible to water logging and responds to soil aeration. Oxygen deficiency at both a temporal and spatial scale could occur for a subsurface drip irrigated crop, particularly in heavy clay soils. Use of aerated water irrigation (oxygation) to overcome hypoxia in the rhizosphere was evaluated in broad-acre chickpea crops in 2006 and 2007, in a heavy clay soil of central Queensland, Australia. The injection of 12% by volume air into subsurface drip irrigation water (oxygation) to two consecutive broad-acre chickpea crops resulted in a beneficial effect on yield (gains of 27% and 10% for 2006 and 2007, respectively), but the effect of irrigation regimes at deficit and full irrigation (85 and 100% ETc) was not significantly different. Chickpea yield with aerated subsurface drip irrigation was much higher (3.24 and 2.05 t ha-1) compared to the 7-year (2008–2015) national average yield (1.13 t ha-1). The aerated irrigation resulted into significantly higher gross production water use index (GPWUI) and irrigation water use index (IWUI) particularly in the year when the crop was planted early in the season. There was no significant difference in response to either of these water use efficiency (WUE) indicators between irrigation treatments, with the exception of a significantly enhanced IWUI with the 85% ETc in the first season. These results were consistent with those for cotton on the same site, providing further justification for the capital investment required for oxygated subsurface drip irrigation (SDI) system. Highlights • Aerated water for sub-surface drip irrigation improved chickpea yield by 10–27% compared to the control. • Chickpea yields with subsurface drip irrigation were 81–187% higher than the national average of 1.13 t ha-1. • Aerated water irrigation increased gross production water use index and irrigation water use index for chickpea in a Vertosol. [ABSTRACT FROM AUTHOR]

The concept of carbon (C) saturation implies that soils have a finite capacity to store C in a stable form, depending on their silt + clay content. We hypothesized that the stabilization of added organic C would be low in C saturated soil. We tested experimentally the influence of C saturation deficit on stabilization of added grass residue. We incubated 12 highly weathered, oxic soil samples collected from three contrasting land uses (i.e. cropping, improved pasture, and forest) with grass residue for 8 months. Carbon saturation deficit of the forest soils was lower than pasture and cropping soils. After incubation, we found increases in silt + clay associated C in grass residue treatment positively correlated with C saturation deficit of soils. Our results suggest that stabilization of added C was high in soil with low C saturation level and hence higher C saturation deficit. [ABSTRACT FROM AUTHOR]

Tillage and nitrogen (N) fertilization have been shown to affect soil abiotic and biotic properties, but it is unclear how these impact long-term tillage systems in subtropical climates. We studied a 48-y wheat cropping trial in semi-arid, subtropical Australia that applied different tillage practices (no-till [NT] and conventional till [CT]) and N fertilization rates (0 and 90 kg N ha-1, 0 N and 90 N, respectively) in a Vertisol from 0 to 10 cm soil depth. Total organic carbon (TOC) significantly increased only when N fertilizer was applied under NT. Total nitrogen (TN) concentrations increased when N fertilizer was applied but were unaffected by tillage. N-acetyl-β- D -glucosaminidase (NAG) activity was highest when N was applied and α-glucosidase (α-Glu) activity was lowest in the NT and 0 N treatments. Activities of β-glucosidase, phenol oxidase and phosphatase were unaffected by the management practices. While the bacterial community composition appeared most distinct in NT and 0 N conditions, fungal community composition, and bacterial and fungal alpha diversity remained unaffected by the treatments. Although wheat yield was only significantly influenced by N fertilization rates, both NT and N fertilization may be preferable for management as these soils had the most favorable TOC, TN, and enzymatic activity. These differences seen between treatments here are less pronounced than reported elsewhere, with this likely a result of the high clay content of the soil which can have a buffering capacity, or that these treatments have less of an impact over longer time scales. Nevertheless, we conclude that no-tillage and N fertilization remain important in influencing soil properties and functioning over decades in this Vertisol in a semi-arid subtropical region. • Total organic carbon significantly increased when N was applied under no-till (NT). • Total N increased when N fertilizer was applied but there was no effect of tillage. • N-acetyl-β- D -glucosaminidase activity was highest when N was added. • Bacterial community composition was most distinct in NT and no N addition treatment. • Fungal community composition and bacterial alpha diversity were not affected. [ABSTRACT FROM AUTHOR]

The expansion of irrigation infrastructure in Tasmania, Australia, has led to intensified irrigated crop production, including for vegetables. This has resulted in increased irrigation of texture contrast soils, and other soils with high clay content in the subsoil. Widely used for rain-fed grain production in other parts of Australia, these soils have been subject to a range of soil amelioration approaches in an effort to improve their soil physical characteristics and capacity to produce crops. Subsoil manuring – the process of placing organic soil ameliorants at a target depth using a specially modified deep ripper – has proven to be successful in increasing yields of rain-fed grain crops. Locally available organic materials (chicken manure and poppy seed meal) were placed in the upper zone of a clay subsoil at three sites used for irrigated vegetable production. The crops grown were green peas for processing and carrots for seed production. Normal grower management practices were the reference against which treatments were compared. Subsequent measurements showed no consistent or significant benefit from subsoil manuring one year after treatment under the soil and crop management conditions used in this research. • Subsoil manuring has shown productivity benefits in rain-fed grain production. • Irrigated vegetables were grown on treated texture contrast and high clay soils. • No significant differences were found as a result of subsoil manuring treatments. [ABSTRACT FROM AUTHOR]

[Display omitted] • FTIR spectroscopy of clay is sensitive to temperature during bushfires. • Boron leached from combusted bark decreases d11B of clays. • No direct influence of combustion temperature on d11B of clays. • Clays have higher d11B after experiencing a high severity fire. • Both FTIR spectroscopy and B isotope could be viable fire proxies. Bushfire occurrences will likely be exacerbated by climate change, thus requiring a model to forecast and manage their impacts. However, a robust bushfire model requires new proxies that can infer fire severity responses to past climate variability. A key test to the viability of new fire proxies is whether they record fire severity in the affected soil. We address this by testing Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR) spectroscopy and boron (B) isotopes in soil clay fractions from Yengo National Park, southeastern Australia, as proxies for bushfire severity. The isotopic results were also compared to that of clays that reacted with experimentally combusted bark. ATR-FTIR spectroscopy constrains the soil temperature to between 225 and 500 °C during high severity fires, based on the lack of dehydroxylation peak characteristics and the increased aromatic to aliphatic organic peak ratios in clays, compared to that of low severity sites. The isotope composition of the non-exchangeable B fraction in clays is lighter after reacting with leaching solutions of bark combusted at higher temperatures. Combustion temperature does not affect the B isotope fractionation during B adsorption onto clays. Changes to the B isotope composition of clays could instead be justified by the varying B concentration and B isotope compositions of the leaching solutions. In Yengo soil clay fractions, sites that experienced a high severity fire show higher δ 11B values by about 1.5 ‰, compared to low severity sites- at odds with observations from our experiment using combusted bark. The combustion of leaves from tree crowns in high severity fires could account for the increase in δ 11B of clays post-fire. In summary, FTIR spectroscopy of clays could be useful for constraining soil temperature during bushfires, while the B isotope composition of clays appears as a promising proxy for fire severity. [ABSTRACT FROM AUTHOR]

Dispersive soil has poor physical properties, which reduce porosity, air and water movement. These properties can reduce crop production and create problems with soil stability under buildings and infrastructure. Traditionally, clay dispersion has been related to the exchangeable sodium percentage ( ESP) of soil or to the sodium adsorption ratio ( SAR) of soil solutions. However, the roles of the other exchangeable cations, potassium and magnesium, in clay dispersion have been debated in the literature and their importance is unresolved. Based on the relative dispersive and flocculating powers of sodium, potassium, magnesium and calcium, a new concept for describing dispersive soil is proposed. This defines the net dispersive charge as the difference between the dispersive charge, calculated from the concentration of exchangeable cations measured at a given soil pH and their dispersive powers, and the flocculating charge, calculated from the concentrations of cations in dispersed solutions and their flocculating powers. The net dispersive charge of a soil determines the clay dispersion. Clay disperses when the net dispersive charge is positive and does not disperse when it is zero or negative. This new concept resolves controversies in the literature caused by the roles of organic matter, clay mineralogy, exchangeable cation composition and electrolyte concentration in relation to clay dispersion. Experimental confirmation of this concept is provided by the analytical data of 96 soil samples collected from different parts of South Australia and Victoria in Australia and from previously published data. Possible methods of estimating net dispersive charge from soil solutions are discussed. Highlights Examined the role of different exchangeable cations in inducing clay dispersion., The long-debated issue of the importance of different cations in dispersive soil is resolved., The net dispersive charge in soil is related to the amount of dispersed clay., Reclamation of dispersive soil requires the net dispersive charge to be zero. [ABSTRACT FROM AUTHOR]

Soft clay becomes remoulded around wick drains during their installation. The effects of remoulding can be taken into account in design by adopting an analytical method incorporating the radius of smear and the permeability of the remoulded soil in the smear zone. However, these parameters are usually not known and are estimated largely based on experience and guidance provided in the technical literature. Back analysis of settlement data from an embankment constructed on soft Pimlico Clay in Australia with a wick drain spacing of 1·5 m in an equilateral triangular configuration is performed to assess the potential smear parameters. A chart showing variations of permeability with smear radius is presented to assist with selection of design parameters for wick drains installed in soft Pimlico Clay. Effects of wick drain spacing on the permeability of the remoulded soil are investigated through back analysis of embankments constructed on wick drains spaced at 1·0 m and 1·35 m in an equilateral triangular configuration. Although the embankments are not constructed in identical ground conditions, there is no evidence that reducing the spacing between the wick drains causes the average permeability ratio to increase. [ABSTRACT FROM AUTHOR]

Droughts are increasing in frequency and severity in many regions of the world and there are uncertainties how recurrent drought will impact acid sulfate soils, which can undergo extreme and persistent acidification (pH < 4) following oxidation. Using column experiments, we induced a 9 week drought/drying and 9 week rewetting phase in two acid sulfate soil profiles with sulfuric (pH < 4) and hypersulfidic materials from the Lower River Murray region of Australia's largest river system. These soils had not yet recovered from the extreme period of the 'Millennium Drought' between 2007 and 2010. pH, redox potential, dissolved metals and greenhouse gases (CO 2 , CH 4 and N 2 O) were measured at multiple depths in each column every 3 weeks during the drying and rewetting phases. The solid phase of the Sulfuric and Hypersulfidic clay soil profiles in both column experiments were analysed for complete acid-base accounting (actual and retained acidity, potential acidity in the form of pyrite, and acid neutralising capacity) and reactive metals at the beginning and end of the experiment. Residual pyrite, present in high concentrations in the Sulfuric clay soil column, oxidised during the drying period, further lowering the pH (<4) and mobilising dissolved metals (Al, Cd, Cu, Ni, Zn). More reactive Fe and Al phases were formed during the drying-rewetting cycle while reactive Mn decreased. The soil pH did not recover (i.e. increase) during the rewetting phase in both the Sulfuric and Hypersulfidic clay soils, likely due to barriers to microbial reduction reactions, although Fe-oxidising bacteria were likely still active as CO 2 was released. Acid sulfate soils may not recover in inter-drought periods and more severe impacts can be expected following recurrent droughts. • Droughts expose acid sulfate soils causing severe and prolonged impacts. • Column experiments simulated repeated drought in acid sulfate soils. • Soil pH decreased and metals increased during the drying phase. • Soils did not recover upon rewetting. • Recurrent drought in acid sulfate soils creates significant additional risks. [ABSTRACT FROM AUTHOR]

Abstract: Iron (Fe) biogeochemistry is potentially of environmental significance in plantation-forested, subtropical coastal ecosystems where soil disturbance and seasonal water-logging may lead to elevation of Fe mobilization and associated water quality deterioration. Using wet-chemical extraction and laboratory cultivation, we examined the occurrence of Fe forms and associated bacterial populations in diverse soils of a representative subtropical Australian coastal catchment (Poona Creek). Total reactive Fe was abundant throughout 0–30 cm soil cores, consisting primarily of crystalline forms in well-drained sand soils and water-logged loam soils, whereas in water-logged, low-clay soils, over half of total reactive Fe was present in poorly-crystalline forms due to organic and inorganic complexation, respectively. Forestry practices such as plantation clear-felling and replanting, seasonal water-logging and mineral soil properties significantly impacted soil organic carbon (C), potentially-bioavailable Fe pools and densities of S-, but not Fe-, bacterial populations. Bacterial Fe(III) reduction and abiotic Fe(II) oxidation, as well as chemolithotrophic S oxidation and aerobic, heterotrophic respiration were integral to catchment terrestrial Fe–C cycling. This work demonstrates bacterial involvement in terrestrial Fe cycling in a subtropical coastal circumneutral-pH ecosystem. [Copyright &y& Elsevier]

In grassland reserves, managed disturbance is often necessary to maintain plant species diversity. We carried out experiments to determine the impact of fire, kangaroo grazing, mowing and disc ploughing on grassland species richness and composition in a nature reserve in semi-arid eastern Australia. Vegetation response was influenced by winter–spring drought after establishment of the experiments, but moderate rainfall followed in late summer–autumn. Species composition varied greatly between sampling times, and the variability due to rainfall differences between seasons and years was greater than the effects of fire, kangaroo grazing, mowing or disc ploughing. In the fire experiment, species richness and composition recovered more rapidly after spring than autumn burning. Species richness and composition were similar to control sites within 12 months of burning and mowing, suggesting that removal of the dominant grass canopy is unnecessary to enhance plant diversity. Two fires (separated by 3 years) and post-fire kangaroo grazing had only minor influence on species richness and composition. Even disc ploughing caused only a small reduction in native richness. The minor impact of ploughing was explained by the small areas that were ploughed, the once-off nature of the treatment, and the high degree of natural movement and cracking in these shrink-swell soils. Recovery of the composition and richness of these grasslands was rapid because of the high proportion of perennial species that resprout vegetatively after fire and mowing. There appears to be little conservation benefit from fire, mowing or ploughing ungrazed areas, as we could identify no native plant species dependent on frequent disturbance for persistence in this grassland community. However, the ability of the Astrebla- and Dichanthium-dominated grasslands to recover quickly after disturbance, given favourable seasonal conditions, suggests that they are well adapted to natural disturbances (e.g. droughts, fire, flooding and native grazing). [ABSTRACT FROM AUTHOR]

Vertisols are clay soils that are common in the monsoonal and dry warm regions of the world. One of the characteristics of these soil types is to form deep cracks during periods of extended dry, resulting in significant variation of the soil and hydrologic properties. Understanding the influence of these varying soil properties on the hydrological behavior of the system is of considerable interest, particularly in the retrieval or simulation of soil moisture. In this study we compare surface soil moisture (θ in m3 m-3) retrievals from AMSR-E using the VUA-NASA (Vrije Universiteit Amsterdam in collaboration with NASA) algorithm with simulations from the Community Land Model (CLM) over vertisol regions of mainland Australia. For the threeyear period examined here (2003-2005), both products display reasonable agreement during wet periods. During dry periods however, AMSR-E retrieved near surface soil moisture falls below values for surrounding non-clay soils, while CLM simulations are higher. CLM θ are also higher than AMSR-E and their difference keeps increasing throughout these dry periods. To identify the possible causes for these discrepancies, the impacts of land use, topography, soil properties and surface temperature used in the AMSR-E algorithm, together with vegetation density and rainfall patterns, were investigated. However these do not explain the observed θ responses. Qualitative analysis of the retrieval model suggests that the most likely reason for the low AMSR-E θ is the increase in soil porosity and surface roughness resulting from cracking of the soil. To quantitatively identify the role of each factor, more in situ measurements of soil properties that can represent different stages of cracking need to be collected. CLM does not simulate the behavior of cracking soils, including the additional loss of moisture from the soil continuum during drying and the infiltration into cracks during rainfall events, which results in overestimated θ when cracks are present. The hydrological influence of soil physical changes are expected to propagate through the modeled system, such that modeled infiltration, evaporation, surface temperature, surface runoff and groundwater recharge should be interpreted with caution over these soil types when cracks might be present. Introducing temporally dynamic roughness and soil porosity into retrieval algorithms and adding a "cracking clay" module into models are expected to improve the representation of vertisol hydrology. [ABSTRACT FROM AUTHOR]

Hydraulic lift can be a desirable characteristic for cotton growing in areas that experience frequent drying of the topsoil. This study employed specialized soil columns to test if cotton can hydraulically lift water and whether this hydraulically lifted water can facilitate P acquisition from the dry topsoil of a clay and a sandy soil. The role of subsoil P placement on cotton growth was also tested. By using a Theta probe, hydraulic lift was detected in the clay soil for 7 days after water was withheld from the topsoil. However, in the sandy soil, a significant overnight increase in soil water was only detected for one day for the treatment with subsoil P application. Where P was applied to the topsoil, and water was withheld, cotton roots showed significant root P uptake from the sandy soil, but negligible P uptake from the clay soil. Irrespective of topsoil watering, the higher root length density in the subsoil of the clay soil accounted for the pronounced response to deep P placement. This study demonstrated that soil texture affects the amount and longevity of hydraulic lift from cotton roots. Hydraulic lift detected in the clay soil did not aid P acquisition from dry surface soil by cotton plants. [ABSTRACT FROM AUTHOR]

Abstract: The saturated hydraulic conductivity (K s) of sulfuric horizons exerts a fundamental control on the connectivity between shallow groundwater and drains in coastal acid sulfate soils (CASS), strongly influencing rates of lateral seepage towards or from field drains. The K s of sulfuric horizons was assessed on seven major coastal floodplains of eastern Australia using an in situ recovery technique conducted in ~0.4–0.65 m deep pits. Duplicate recovery tests were conducted in a total of 148 pits located in 32 separate geomorphic units across the seven coastal floodplains. Most pits were constructed in clay soils with acidic (pH<4.0) shallow groundwater. The K s spanned four orders of magnitude, ranging from <0.5 m day−1 to >500 m day−1. Data are log normally distributed and the median K s was ~15.4 m day−1. Over 40% of the pits had values >20 m day−1, challenging the assumption that K s in sulfuric horizons in CASS landscapes is generally low. Visual observations confirm that high K s values were strongly associated with macropore flow. These data demonstrate that K s in coastal floodplain sulfuric horizons can be very high and is extremely variable within individual floodplains. These findings highlight the need for site specific assessments of soil hydraulic properties in CASS in order to ensure appropriate design and application of acid management techniques. [Copyright &y& Elsevier]

Savanna regions are increasingly developed for agriculture to support population growth, food demand and export economies. This is driving interest in the conversion of natural savanna to cattle grazed pastures or horticultural crops in Northern Australia. Savanna clearing leads to aboveground carbon (C) loss but impacts below-ground are less certain as studies have focused on high rainfall regions, low reactive clay soils and shallow depths of 0.3 m or less. To examine impact of land use change (LUC) in Northern Australia, we sampled the upper 1.0 m soil profile of: 1) savanna woodlands, 2) old and young C4 perennial cattle grazed pastures and 3) old and young, melon-sorghum rotation fields. Soil C concentrations and soil bulk density in the upper 0.3 m were significantly greater in cattle grazed pastures than savanna woodland, such that savanna to pasture LUC significantly increased soil C density from 30.2 ± 1.5–43.4 ± 3.0 Mg C ha-1 over 28 years. Soil bulk density in the upper 0.7 m of savanna woodland was significantly less than that in the melon-sorghum rotations. In contrast, soil C concentrations below 0.5 m were significantly greater in the savanna woodland than in the 3 y.o. melon-sorghum rotation fields. There was no significant difference in soil C density between savanna woodland and 12 y.o. melon-sorghum rotations. This may relate to the beneficial effects of ploughing in sorghum as a green manure, or simply that the decrease in soil C concentration was offset by increased soil C density in the upper layers of soil where most C is located. In contrast, conversion of savanna to cattle grazed pasture sites is equivalent to a soil sequestration rate of 0.34 Mg C ha-1 y-1, approximately 50% of the observed net ecosystem productivity estimated using eddy covariance methods. Changing the depth to which soil C density was estimated changed significant differences amongst land-use systems. Whereas, estimating soil C density using a 'fixed depth' or 'equivalent mass' method did not change the statistical significance. There is an increasing focus on the potential of soil carbon sequestration especially in north Australia and understanding potential change and impact of accounting methods is essential for meaningful policy development. Policy settings to maintain, or improve, soil C storage and soil health may contradict agricultural development goals. • Soil C was measured to 1.0 m under savanna woodland, pasture and cropping systems. • Converting savanna to pasture significantly increased soil C density in the upper 0.3 m. • Melon-sorghum rotation cropped soil had significantly greater bulk density than savanna in the upper 0.5 m. • Converting savanna to melon-sorghum rotation cropping did not significantly change soil C density. • Estimating soil C density to 0.3, 0.6 or 1.0 m changed statistical significant differences. [ABSTRACT FROM AUTHOR]

Two species of root-lesion nematode (predominantly Pratylenchus thornei but also P. neglectus) are widespread pathogens of wheat and other crops in Australia's northern grain belt, a subtropical region with deep, fertile clay soils and a summer-dominant rainfall pattern. Losses in grain yield from P. thornei can be as high as 70% for intolerant wheat cultivars. This review focuses on research which has led to the development of effective integrated management programs for these nematodes. It highlights the importance of correct identification in managing Pratylenchus species, reviews the plant breeding work done in developing tolerant and resistant cultivars, outlines the methods used to screen for tolerance and resistance, and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematode populations and limit crop damage. The declining levels of soil organic matter in cropped soils are also discussed with reference to their effect on soil health and biological suppression of root-lesion nematodes. [ABSTRACT FROM AUTHOR]

The pile designer in a seismically active region will generally need to estimate the maximum seismically induced internal moment and shear of the pile in order to provide adequate strength to maintain the structural integrity of the pile. In this paper an effort has been made to provide a simple means of carrying out such an estimation for a single pile embedded in a homogeneous clay layer. The results have been presented in the form of design charts that can be used directly by designers with no or little computational effort. The variables in the design charts include the length and diameter of the pile, the Young's modulus of the pile material, the strength and stiffness of the soil, and the factor of safety against axial failure of the pile. The charts have been obtained from a time domain analysis of pile-soil interaction, and are based on the response of the piles to a range of earthquakes recorded in North America and Australia. [ABSTRACT FROM AUTHOR]

To have an effective barrier against invading termites around building structures and to assess the potential risks to the urban environment and human beings, we need to understand the fate of termiticides applied in urban soil. The movement and degradation of a new termiticide, fipronil, were investigated in Australian soils following standard termiticide treatment methods (surface application under slab and trenching treatments along walls). Surface application studies in three field sites showed slow dissipation and little movement for fipronil in all three soils under the simulated slab during a three-year period. The greatest mass of the chemical residues remained in the quartzite sand layer (thickness, 5 cm), and only small amounts of these were found to have migrated into the soil layers (depth, 0-15 cm) underneath the quartzite sand layer. Of the three metabolites (desulfinyl, sulfide, and sulfone) found in the soils, the sulfone derivative had the highest concentration. Persistence of fipronil was affected by application rate. The time for 50% loss of the total toxic components (fipronil plus its metabolites) in the quartzite sand layer (thickness, 5 cm) ranged from 200 to 326 d for the low rate (0.15 g active ingredient/m2) and from 633 to 674 d for the high application rate (3 g active ingredient/m²). One-year trenching studies at two sites in Adelaide (Roseworthy Farm [RF] and Terretfield [TF]; South Australia, Australia) showed that vertical movement and dissipation of fipronil occurred in the soils. The average concentration of fipronil in the trenches (depth, 0-30 cm) decreased from 33.7 to 14.9 mg/kg in the loam soil at the RF site and from 39.4 to 14.6 mg/kg in the clay soil at the TF site over the year. With time under the natural weather condition, fipronil and its derivatives were found in the deeper soil sections without treatment (depth, 20-30 cm). However, laboratory studies using repacked soil columns showed low mobility in the loam soil from the RF site and a variably charged clay soil from Malanda (Queensland, Australia) under intermittent wetting and drying conditions. [ABSTRACT FROM AUTHOR]

The response of introduced ( Pennisetum clandestinum Hochst.) and native ( Stipa aristiglumis F. Muell., Themeda australis (R. Br.) Stapf, Danthonia spp. (L.) grasses to the herbicide atrazine was studied in plants with the potential for use in vegetated filters (biofilters) designed to reduce chemical loads in agricultural runoff. The response was detected by photosynthetic inhibition using leaf chlorophyll fluorescence. With continuous short-term (14 days) dosing with atrazine in sand culture, P. clandestinum showed the greatest tolerance, regardless of the dose (20–500 μg/L). In a clay vertosol soil in the glasshouse, the four species were tolerant to longer-term (84 days) application of three successive doses of simulated run-on, each dose containing 100 μg/L atrazine, a concentration which is comparable to the highest reported in runoff from agricultural land in Australia. Even with a subsequent single atrazine dose at ∼ ∼5000 μg/L, established plants of the four species showed signs of quick recovery (7–21 days) to normal photosynthetic activity. In a field experiment with simulated run-on, applied to P. clandestinum pasture in sandy loam soil, repeated doses at concentrations up to 1000 μg/L gave no significant response; only a subsequent single dose of 5000 μg/L had significant effects, from which plants soon recovered. Although damage from atrazine can be demonstrated with continuous dosing in non-adsorbing media, in soil culture the tolerance of the four selected species to repeat doses of atrazine shows they may be used confidently for biofiltering purposes. P. clandestinum was especially tolerant. [ABSTRACT FROM AUTHOR]

A large part of Australia's broad acre irrigation industry, which includes cotton, is farmed on heavy clay Vertosols. Recent changes in nematicide chemical availability, changes in rotations and the observation of the reniform nematode in central Queensland has highlighted that we need to improve our understanding of nematodes in these soils. We undertook preliminary investigations into distribution by depth under a cotton-cotton and cotton-maize rotation as well as vertical movement experiments in microcosms to better understand nematode distribution and movement in heavy clay soils. Analysis revealed that field populations decreased with soil sample depth, but there were also differences between rotations. In microcosm experiments, vertical movement of nematodes in these heavy clay soils was restricted, even in the presence of plant roots and moisture, both of which were hypothesised to improve nematode migration. The results imply that crop rotation currently remains a plausible option for nematode control, and that we still have a lot to learn about the ecology of nematode populations in Vertosols. [ABSTRACT FROM AUTHOR]

• Groundwater recharge mapped in an urbanising catchment using multiple techniques. • Recharge restricted to specific geographic areas where volcanic clays are absent. • Approximately half of recharge occurs over 15% of the land area. • Future land use planning must prioritize protection of high recharge areas. Understanding how land-use change influences the water cycle is of critical importance to land and water management. Determining the timing, location and rates of groundwater recharge and their relationship to land-use is often challenging, leading to significant uncertainties in water budgets and water cycle planning. In this study, a combination of physical and hydrochemical/isotope techniques were used to estimate and map groundwater recharge rates and identify its key controlling factors in a rapidly urbanising catchment in southeast Australia. The primary objective was to provide qualitative and quantitative information regarding recharge, allowing comparison and monitoring of changes as future urbanisation takes place. The presence of significant tritium in shallow groundwater (>1.0 TU), along with radiocarbon activities > 85 pMC and low salinity (e.g. EC < 600 µs/cm) allowed identification of areas where significant recharge has taken place in recent years. These were strongly associated with elevated topography on the basin margin, and the absence of volcanic clay - the dominant lithology underlying most of the region. This interpretation is supported by time-series analysis of soil moisture profiles, which indicate minimal vertical propagation of precipitation below 1.5 m depth in volcanic clay soils. Estimation of recharge rates was conducted using chloride mass balance and water table fluctuation analysis in water table aquifer monitoring bores. Rates mostly ranged between 1.5 and 50 mm/yr; however, recharge exceeding 100 mm/year was identified in a spatially restricted zone at the edge of the basin. Here, the volcanic lithology is absent and Quaternary sand directly overlies the lower Cainozoic sand aquifer. This area comprises a small percentage of land in the study area (approximately 15%) but is estimated to contribute a large proportion (nearly half) of recharge. The findings underscore the importance of characterising recharge locations and processes to support the protection of groundwater quality and quantity, for example, through careful land-use planning. [ABSTRACT FROM AUTHOR]