bluuebunny/crossref_metadata_2025 huggingface dataset:
Soil microbial biomass, C and N mineralization, and enzyme-activities in a hill pasture - Influence of grazing management
Authors: Ross DJ , Speir TW , Kettles HA , Tate KR , Mackay AD
Published: April 2005

Grazing and fertilizer management practices are of prime importance for maintaining summer-moist hill pastures of introduced grasses and clovers in New Zealand for sheep and cattle production. The influence of withholding grazing (a pastoral fallow) from spring to late summer on microbial biomass, C and N mineralization, and enzyme activities was investigated in a Typic Dystrochrept soil from unfertilized and fertilized (rock phosphate and elemental S) low-fertility pastures at a temperate hill site. The fallow increased pasture but not legume growth in the following year in the unfertilized treatment, but had no effect on pasture or legume growth in fertilized plots. High background levels of the biochemical propel-ties examined, and very variable rates of N mineralization, complicated data interpretation. Extractable-C concentration and CO2-C production were enhanced at the completion of the fallow. Increases in net N mineralization (14-56 days incubation), following initial immobilization, after the fallow were clearly indicated in the unfertilized treatment, but were less distinct, in the fertilized treatment. The fallow had no detectable influence on the concentrations of total C and N or microbial C and P, or on invertase, phosphodiesterase and sulfatase activities. Some small changes in microbial N and an increased proportion of bacteria in the microbial population were, however, suggested. Results are consistent with the concept of fallowing giving a short-term increase in pools of readily decomposable soil organic matter. Generally, the changes that did occur in these soil biochemical properties are, with the partial exception of increased N availability, unlikely to have had any pronounced impact on subsequent pasture performance.
The effects of cultivation on the composition of organic-matter and structural stability of soils
Authors: Golchin A , Clarke P , Oades JM , Skjemstad JO
Published: April 2005

Soil samples were obtained from the surface horizons of five untilled sites and adjacent sites under short- and long-term cultivation. The soil samples were fractionated based on density and organic materials were concentrated in various fractions which enabled comparative chemical composition of the organic materials in cultivated and uncultivated sites by solid-state C-13 CP/MAS NMR spectroscopy. Changes in the nature of organic carbon with cultivation were different in different soils and resulted from variations in the chemistry of carbon inputs to the soils and a greater extent of decomposition of organic materials in cultivated soils. Differences in the chemical composition of organic carbon between cultivated and uncultivated soils resided mostly in organic materials occluded within aggregates, whereas the chemistry of organic matter associated with clay particles showed only small changes. The results indicate a faster decomposition of O-alkyl C in the cultivated soils. Wet aggregate stability, mechanically dispersible clay and modulus of rupture tests were used to assess the effects of cultivation on structural stability of soils. In four of five soils, the virgin sites and sites which had been under long-term pasture had a greater aggregate stability than the cultivated sites. Neither total organic matter nor total O-alkyl C content was closely correlated with aggregate stability, suggesting that only a part of soil carbon or carbohydrate is involved in aggregate stability. The fractions of carbon and O-alkyl C present in the form of particulate organic matter occluded within aggregates were better correlated with aggregate stability (r = 0.86** and 0.88**, respectively). Cultivation was not the dominant factor influencing water-dispersible clay across the range of soil types used in this study. The amount of dispersible clay was a function of total clay content and the percentage of clay dispersed was controlled by factors such as clay mineralogy, CaCO3 and organic matter content of soils. The tendency of different soils for hard-setting and crusting, as a result of structural collapse, was reflected in the modulus of rupture (MOR). The cultivated sites had significantly higher MOR than their non-tilled counterparts. The soils studied had different MOR due to differences in their physical and chemical properties.
Corrigenda - Application of a simple-model to assess the ground-water contamination potential of pesticides
Authors: Di HJ , Kookana RS , Aylmore LAG
Published: April 2005

A simple model is described for assessing the ground water contamination potential of pesticides. This model, based on simple processes of linear, equilibrium and singular partition between solution and soil organic matter, steady convective flow, and first-order degradation, calculates fractions of pesticides remaining in the soil as they leach to greater depth. Possible effects by preferential flow that may be present in structured soils are ignored. The soil profile is divided into a number of layers which may differ in bulk density, moisture content at field capacity, organic C content, and degradation half-life. The leaching depths predicted by this model generally agreed with the mean leaching depths measured in a field study, and with those predicted by the CALF model. The leaching depths by the simple model were also statistically related to those simulated by the LEACHM model, although the values by LEACHM were found to be much higher than those by the simple model and by CALF. Under the soil and environmental conditions given, the simple model predicted that chlorpyriphos and chlorthal dimethyl would not leach to any noticeable depth before being completely degraded, that metribuzin, prometryne, propyzamide and simazine would mostly degrade to insignificant concentrations before reaching 500 cm, and that traces of fenamiphos, metalaxyl and linuron might reach beyond 1000 cm.
Evaluation of the potential to dispose of sewage-sludge. 2. Potential for off-site movements of solids and solutes
Authors: Loch RJ , Costantini A , Barry GA , Best EK
Published: April 2005

This paper reports a study of the potential for off-site movements of pollutants from sewage sludge broadcast onto the soil surface in Pinus plantations established on the coastal lowlands of south-east Queensland. Laboratory studies of size and settling velocity distributions of rainfall-wetted sludge showed that it is relatively coarse and non-erodible. Field rainfall simulation studies at three sites in pine forests near Beerburrum found no significant increase in interrill erosion due to broadcasting of sludge. (Most or all of the sediment was observed to come from mineral soil exposed when a gutter to collect runoff was installed at the downslope ends of the plots.) However, there was considerable movement of solutes in runoff from rainfall simulator plots that had received sludge-either freshly applied or 'consolidated' sludge (that had been broadcast on the plots 6 months prior to the rainfall simulation study and exposed to rain and weathering). Electrical conductivity (EC) of runoff from freshly applied sludge was initially high but decreased steadily during the 30 min rainfall event. Runoff from consolidated sludge had lower ECs, though significantly (P < 0.05) higher than those of runoff from control plots. Concentrations of nitrate-N and ammonium-N were initially high in runoff from freshly applied sludge, but decreased rapidly during the rainfall event. In contrast, concentrations of mineral N in runoff from consolidated sludge were low throughout the rainfall event. These results indicate a significant risk of off-site N pollution if runoff occurs during the first rains following broadcasting of sludge. By contrast, concentrations of total phosphorus, copper, and zinc in runoff from both fresh and consolidated sludge were relatively high, and showed only small decreases during the rainfall event applied. This suggests that sludge will contribute significant quantities of these elements to runoff for extended periods after broadcasting. The implications of these findings become important in terms of the timing and method of sludge application to the soil.
Nitrate leaching from a drained, sheep-grazed pasture. I. Experimental results and environmental implications
Authors: Magesan GN , White RE , Scotter DR
Published: April 2005

Nitrate-nitrogen (N) and chloride concentrations were measured in the drainage from two hydrologically similar mole- and pipe-drained paddocks over 3 years: 1989, 1990 and 1991. Urea (50 kg N/ha) that was applied to both paddocks in early spring 1989 had no effect on the nitrate concentrations in the drainage water. In late autumn 1990, 120 kg N/ha as urea was applied to one of the paddocks, but the nitrate leached in the following winter was equivalent to only 8% Of the fertilizer N. The nitrate concentrations in the drainage were greater than 10 g N/m3 for most of the season, with peak concentrations up to 35 g N/m3, even for the paddock where urea was not applied. The paddocks were periodically mob-grazed by sheep during the monitoring period, but this had no measurable effect on the nitrate and chloride concentrations in the drainage collected during or immediately after grazing.
The effects of grazing pressure on soil animals and hydraulic properties of two soils in semi-arid tropical Queensland
Authors: Holt JA , Bristow KL , Mcivor JG
Published: April 2005

A grazing experiment was used to examine the effects of high grazing pressure on soil Acari populations, and on termite populations and activity, at two sites in semi-arid north Queensland. Changes in soil hydraulic properties were also examined. Our investigations have shown that Acari populations were significantly lower in the heavily grazed treatments at one of the sites. Termite species diversity and activity were significantly lower in the heavily grazed treatments than in the lightly grazed treatments at both sites. The surface soils also had significantly lower steady-state how rates and hydraulic conductivities in the heavily grazed treatments than in the lightly grazed treatments. The deterioration in soil hydraulic properties in the heavily grazed treatments appears to be associated with both increased trampling by cattle and decreased termite activity in the top 25 mm of soil. The surface and near surface galleries constructed by detritiverous termites therefore have an important function in water movement in these semi-arid soils.
Comparison of seven phosphorus sorption indices
Authors: Bolland MDA , Gilkes RJ , Brennan RF , Allen DG
Published: April 2005

Seven methods of estimating or predicting phosphorus (P) sorption capacity were compared for 47 neutral to acid Western Australian soils. Two methods, the P buffer capacity (PBC) and the Fox and Kamprath procedure, provided reliable indices of P sorption from well defined P sorption isotherms, but they are not quick routine methods because several levels of P addition are required. The other five routine procedures included two versions of the P retention index (PRI), determined by adding one level of P, and three soil properties, oxalate extractable iron (oxalate Fe), oxalate extractable aluminium (oxalate Al), and pH measured in sodium fluoride [pH (F)], that are known to indicate P sorption capacity. All the indices were well related to one another. The oxalate Fe index was the least well related to PBC whereas oxalate Al, one of the PRI indices, and pH (F) were closely related to PBC and could be used as quick, economical procedures to assess the P sorption capacity of soils.
Soil management and rroduction of alfisols in the semi-arid tropics. I. Modelling the effects of soil management on runoff and erosion
Authors: Littleboy M , Cogle AL , Smith GD , Yule DF , Rao KPC
Published: April 2005

Techniques to simulate effects of surface cover and tillage on runoff and erosion are described. Data for 15 soil management treatments on an Alfisol in the semi-arid tropics, India, were used to modify existing procedures of runoff prediction using USDA runoff curve numbers. A relationship between surface cover and curve number was developed to account for the effects of surface cover on runoff. Impact of shallow or deep tillage was predicted using functions that relate curve number to cumulative rainfall since tillage. The derived relationships were applied to adjust curve number due to the effects of cover and tillage on a daily basis and were incorporated into the cropping systems model called PERFECT-IND. Results of model validation showed that PERFECT-IND explained between 71 and 91% of the variation in daily runoff volumes. The model also provided accurate predictions of average annual runoff ranging from 33 to 217 mm for the 15 soil management treatments. Runoff was reduced to a much greater extent by surface cover compared with surface roughness. Surface cover reduced runoff curve number by a maximum of 35 units. The maximum reduction in curve number due to surface roughness was 5 units for shallow tillage and 10 units for deep tillage. Erosion predictions were acceptable but the lack of erosion data for all years in the experimental data limits the confidence in model output. Model calibration and validation have provided a set of parameters that can be coupled with historical climate records to provide a long-term perspective of the effects of soil management on runoff and erosion.
Soil management and production of alfisols in the semi-arid tropics. II.* Deriving USDA curve numbers from rainfall simulator data
Authors: Littleboy M , Sachan RC , Smith GD , Cogle AL
Published: April 2005

A comparison of USDA-SCS runoff curve numbers from model calibration using experimental runoff data and rainfall simulation is presented. A rainfall simulator was used to derive curve numbers for a range of antecedent soil water contents and surface cover conditions for an Alfisol soil in the semi-arid tropics of India. These relationships between cover and curve number are compared with relationships that were obtained using model calibration in Part I of this paper. The results showed that rainfall simulation on dry soils was most useful for deriving curve numbers. Derived curve numbers under dry antecedent conditions (CN1) can be easily adjusted to curve numbers for average antecedent conditions (CN2) which is an input parameter for many agricultural simulation models. Further analysis of the effects of cover on curve number showed that a linear function explained up to 86% of the variability between curve number and surface cover. Curve numbers derived from rainfall simulators were similar to those obtained from model calibration. This has improved confidence in using rainfall simulation to measure a runoff curve number.* Part I, Aust. J. Soil Res. 1996, 34, 91–102.
Soil management and production of alfisols in the semi-arid tropics. IV.* Simulation of decline in productivity caused by soil erosion
Authors: Littleboy M , Cogle AL , Smith GD , Rao KPC , Yule DF
Published: April 2005

Maintenance of a productive soil base by minimizing soil erosion is vital to long-term crop production. In this study, a modelling approach is used to estimate the effects of soil erosion on productivity for a sorghum cropping system on an Alfisol in the semi-arid tropics of India. Predictions of erosion, runoff and yield decline due to erosion, for variations in initial soil depth, slope, tillage strategy and amendment treatment, are presented. On average, soil depth decreased by 0.91 cm/year at Hyderabad for a 10% slope, 80 cm initial soil depth, shallow tillage at planting and no surface amendment. Rates of soil removal and subsequent yield decline were higher for shallower soils, steeper slopes and if management practices provided less surface cover during the crop. The productive life of the soil was less than 91 years for some soil depths, slope and management combinations. For other combinations, significant yield decline was predicted after 91 years of cropping. The quantification of erosion-productivity relationships allows us to identify regions with a higher risk of degradation from soil erosion and to estimate the impact of various management options on long-term sustainability. Models provide a basis to focus research and a means of assessing alternative management strategies to preserve long-term production.* Part III, Aust. J. Soil Res. 1996, 34, 113–125.
An assessment of a daily rainfall erosivity model for New South Wales
Authors: Yu B , Rosewell CJ
Published: April 2005

A rainfall erosivity model using daily rainfall amounts to estimate rainfall erosivity was tested for 29 sites in New South Wales to see whether such a model could adequately describe the temporal variation and seasonal distribution of rainfall erosivity. The coefficient of determination varied from 0.57 to 0.97 and the average discrepancy between actual and estimated seasonal distribution was no more than 3%. A set of parameter values for sites without pluviograph data was recommended for New South Wales. With this set of recommended parameter values, the percentage of total variance explained was decreased to 44%–89% for the 29 sites. Large errors, however, can occur when estimating extreme storm erosivity with large return periods. The daily erosivity model could be used for determining the seasonal distribution of rainfall erosivity or for simulating changes to rainfall erosivity as part of climate change impacts assessment.
Use of airborne gamma radiometric data for soil mapping
Authors: Cook SE , Corner RJ , Groves PR , Grealish GJ
Published: April 2005

Variations of naturally emitted gamma radiation have been used in geological prospecting for over 20 years to detect anomalies associated with exploitable ore deposits. We examined their ability to detect spatial variation of soil material by comparing simultaneous ground and airborne measurements of gamma emissions with ground observations over a catchment in south-western Australia. Measurements were taken in the spectral windows for 40K, 238Uand 232Th. Variations of gamma radiation corresponded with the distribution of soil-forming materials over the landscape, and were used to distinguish between highly weathered residuum and fresh material from granitic outcrops. Gamma radiometric data also discriminated clearly between doleritic, lateritic and granitic soil parent materials. Airborne data indicated the distribution of these materials through the catchment, with the exception of dolerite dikes, which were too narrow to be detected using pixels greater than 20 m wide. It is concluded that gamma radiometric data can provide valuable insights into the spatial distribution of soil-forming materials but, given their limitations to provide direct information of pedological alteration, such data are likely to prove most valuable to soil survey when considered jointly with other information such as terrain models or aerial photography.
Water retention in Australian soils. I. Description and prediction using parametric functions
Authors: Cresswell HP , Paydar Z
Published: April 2005

The soil water characteristic (SWC) is a fundamental property controlling soil water storage and movement. The SWC is often described by analytical functions because this is convenient in the solution of numerical flow equations as well as in implementation of closed-form methods of predicting unsaturated hydraulic conductivity. The analytical functions must adequately describe the measured SWC data for these applications to be successful. We used two large sets of SWC data from Australian soils to evaluate five widely used equations on the basis of how well they describe the measured data. In general, sigmoidal equations described the measured SWCs best, but the simpler power-law equations also gave a very good description. Most of the error with the power-law functions occurred at water contents near saturation from physically unrealistic equation discontinuity around the air entry potential. The good performance of the power-law equations enabled development of a method to predict SWC data from only two measured SWC points and a knowledge of soil bulk density. When a power-law equation was used together with parabolic smoothing and parameter values were obtained using just two measured SWC points, then a very good SWC prediction was obtained within the 0 to -150 m matric potential range. This method does increase the reliance on the accuracy of measurement of the two points that are used for interpolation or extrapolation. The 'two-point' prediction method significantly reduces the cost of obtaining SWC data, thus easing an important constraint to the widespread application of soil water simulation models based on Richards' equation.
Storage of air-dry soil samples at 0 degrees C or at room temperature before analysis does not affect bicarbonate soil-test phosphorus
Authors: Bolland MDA , Allen DG
Published: April 2005

Five levels of phosphorus (P), as powdered single superphosphate, were incubated in moist soil (field capacity) for 42 days at 50�C in six different soils collected from south-western Australia. The soils were then air-dried for 7 days. Some subsamples of air-dry soil were stored for 180 days at 0�C in a cold room. Other subsamples were stored at fluctuating room temperature (18–25�C) in a laboratory and were sampled at 30, 60, 120, 150 and 180 days after storage to measure bicarbonate-extractable P (soil-test P) by the Olsen and Colwell procedures. No changes in soil-test P were detected while air-dry soil samples were stored at 0�C or room temperature.
The chemistry and nature of protected carbon in soil
Authors: Skjemstad JO , Clarke P , Taylor JA , Oades JM , Mcclure SG
Published: April 2005

The nature of organic carbon in the < 2, 2–20, 20–53, 53–200, and 200–2000 mu m fractions of four surface soils was determined using solid state 13C nuclear magnetic resonance (n.m.r.) spectroscopy with cross polarisation and magic angle spinning (CP/MAS). Analyses were repeated after high energy ultraviolet photo-oxidation was performed on the three finest fractions. All four soils, studied contained appreciable amounts of physically protected carbon while three of the soils contained even higher amounts of charcoal. It was not possible to measure the charcoal content of soils directly, however, after photo-oxidation, charcoal remained and was identified by its wood-like morphology revealed by scanning electron microscopy (SEM) together with a highly aromatic chemistry determined by solid state 13C n.m.r. Charcoal appears to be the major contributor to the 130 ppm band seen in the n.m.r. spectra of many Australian soils. By using the aromatic region in the n.m.r. spectra, an approximate assessment of the charcoal distribution through the size fractions demonstrated that more than 88% of the charcoal present in two of the soils occurred in the < 53 �m fractions. These soils contained up to 0.8 g C as charcoal per 100 g of soil and up to 30% of the soil carbon as charcoal. Humic acid extractions performed on soil fractions before and after photo-oxidation suggest that charcoal or charcoal-derived material may also contribute significantly to the aromatic signals found in the n.m.r. spectra of humic acids. Finely divided charcoal appears to be a major constituent of many Australian soils and probably contributes significantly to the inert or passive organic carbon pool recognised in carbon turnover models.
Comparison of legume-based cropping systems at Warra, Queensland. 2. Mineral nitrogen accumulation and availability to the subsequent wheat crop
Authors: Hossain SA , Strong WM , Waring SA , Dalal RC , Weston EJ
Published: April 2005

Mineral nitrogen release following legume-based cropping systems for restoring the fertility of a Vertisol and the yield response and N uptake of subsequent wheat crops was studied. Legume phases of pastures, including a 4 year grass+legume ley, and lucerne and medic leys (~1 year) were terminated in October 1988 or 1989 and rotated with wheat. Chickpea-wheat rotations matched those of lucerne and medic leys. Mineral N accumulations during a subsequent fallow period were determined by core sampling to 1.5 m in October, February and May. Grain yield and N uptake of wheat enabled comparisons of the fertility restorative effects of the various systems relative to continuous wheat cropping. Averaged for two fallow periods, increases in mineral N down to 1.2 m depth were 93, 91, 68, and 37 kg/ha following grass+legume, lucerne and medic leys, and chickpea, respectively, compared with the continuous wheat treatment. Wheat yields were generally lower in 1989 (1.85–2.88 t/ha) than in 1990 (2.08–3.59 t/ha) following all leys and crops due to seasonal conditions. There was a grain yield increase of 0.11 and 0.52 t/ha in 1989 and 1.23 and 1.26 t/ha in 1990 following lucerne and medic leys, respectively and 0.85 t/ha in 1990 following a 4 year grass+legume ley. Following chickpea there was a yield increase of 0.81 and 1.36 t/ha in 1989 and 1990 respectively. Nitrogen uptake by wheat was increased by 40 and 49 kg/ha in 1989 and 48 and 58 kg/ha in 1990 following lucerne and medic leys respectively and 63 kg/ha in 1990 following a 4 year grass+legume ley. Following chickpea N uptake by wheat was increased by 27 and 32 kg/ha in 1989 and 1990 respectively. Grain protein concentration of wheat was substantially higher following all pasture leys (11.7–15.8%) than following wheat (8.0–9.4%) or chickpea (9.4–10.1%). Therefore, there was substantial evidence of the effectiveness of pasture leys in soil fertility restoration, as reflected in mineral N, yield response and N uptake by subsequent wheat crops.
A model for predicting aeolian sand drift and dust entrainment on scales from paddock to region
Authors: Shao YP , Raupach MR , Leys JF
Published: April 2005

This paper describes a Wind Erosion Assessment Model (WEAM) for the estimation of sand drift and dust entrainment in agricultural areas. Both the sand drift and dust entrainment parts of the model are physically based, utilising a combination of established and recent theoretical and experimental results. Key components of the model include the Owen equation for the saltation flux; the observed and theoretically predicted proportionality between saltation flux and dust entrainment by saltation bombardment; theoretical and experimental results on the amelioration of wind erosion by nonerodible roughness; and new experimental results on the suppression of erosion by surface moisture. The size distribution of the particles on the soil surface (in their natural state) is used as a primary parameter. The model is restricted to a description of the mobilisation of sand and dust in erosion source areas, and specifically excludes treatment of 2 groups of related processes: dust transport away from source areas and its ultimate deposition; and evolution of surface properties, by the wind erosion process itself, by other weathering processes, or by management intervention. The results of the model are compared with data from a portable wind erosion tunnel, and with direct wind erosion measurements at paddock scale. By offering a synthesis of available physical knowledge of sand drift and dust entrainment, the model also indicates key areas of uncertainty.
An Improved capacitance sensor for in situ monitoring of soil moisture
Authors: Nadler A , Lapid Y
Published: April 2005

A low-power, capacitance-based penetrating soil moisture sensor (SMS) is presented. The SMS is battery-operated, inexpensive, and simple to use. The sensor differs from previous capacitance-based devices in 2 aspects: the measured matrix is contained within the sensor; and the air space between the soil and the probe, which adds an undesirable background, is reduced. Soil moisture changes, not dependent on salinity, correlated well with both water matric potential and water content determined gravimetrically. An SMS installed at 0.45 m depth produced a voltage drop of ~15 mV for each mm of applied irrigation water. The SMS is suitable for controlling irrigation, detecting leaks from disposal containers, fuel tanks, or water reservoirs, and monitoring liquid level.
Sulfate and mineralisable organic sulfur in pastoral soils of New Zealand. I. A quasi equilibrium between sulfate and mineralisable organic sulfur
Authors: Watkinson JH , Kear MJ
Published: April 2005

A theory for a rapid quasi equilibrium between native sulfate and labile organic-S in New Zealand pastoral soils is proposed. It is supported by field and laboratory evidence of the relative constancy of sulfate and phosphate-extractable organic-S (and consequently their direct relationship), the restoration of values after positive and negative perturbations, and their correlation with both mineralised sulfate from laboratory incubation, and with annual pasture yield responses to sulfur fertiliser.
Sulfate and mineralisable organic sulfur in pastoral soils of New Zealand. II*. A soil test for mineralisable organic sulfur
Authors: Watkinson JH , Kear MJ
Published: April 2005

Annual pasture yield responses to sulfur, at sites where no sulfur had been added for at least 1 year, correlated well with both soil sulfate and extractable organic-S. However, sulfate was far more subject to interference from external influences, particularly fertilisers, grazing animals, and rain. A soil test is advocated in which both soil sulfate and organic-S are measured. Organic-S, extracted by phosphate (20 mM), is measured to indicate the long-term supplying power of the soil (also related to total organic-C and -S); and sulfate is measured to indicate any additions from external sources, which would have a short-term effect on pasture growth. The latter is estimated as the sulfate in excess of the quasi equilibrium value, based on the organic-S value. Potassium phosphate, in contrast to calcium phosphate, did not inhibit the extraction of organic-S (and organic matter generally) at organic-C ≥ 5%. Consequently, the organic-S extracted by potassium phosphate correlated much better with pasture response to S, and is the recommended extractant. Both potassium and calcium phosphates extracted the same amount of sulfate. The sulfate mineralised during short-term incubation, and the organic-S extracted by 0.5 M sodium bicarbonate did not correlate with S response in pasture as well as organic-S extracted by potassium phosphate. The alkaline bicarbonate extracted about 5 times more organic-S than potassium phosphate, but extracted a similar amount of sulfate.* Part I. Aust. J. Soil Res. 1996, 34, 385–403.
An urban soil study: heavy metals in Glebe, Australia
Authors: Markus JA , Mcbratney AB
Published: April 2005

This study investigated the occurrence of Pb, Zn, Cu, and Cd in the topsoil of an inner-city suburb of Sydney, Australia. The total heavy metal concentrations in the topsoil of Glebe were determined along with their spatial distribution. These concentrations were compared with environmental investigation limits. Stratified random sampling was conducted within 1-ha square areas taking a samples at 1 m separation from each stratum as a means to investigating spatial variation. Total metal concentrations were determined on an aqua regia extract analysed using atomic absorption spectroscopy. Fifty percent of total Pb, Zn, and Cu concentrations and 2.5% of Cd concentrations were above the ANZECC and NH&MRC (Australia & New Zealand Environment Conservation Council and National Health & Medical Research Council) guidelines of 300, 200, 60, and 3 mg/kg, respectively. Some spatial clustering was evident and a geostatistical analysis showed some large high-risk areas. Fuzzy clustering showed 5 groups of increasing contamination. Soil disturbance and distance from road explained 24% of the variation in total Pb concentration, 15% in total Zn and Cu concentrations, and 13% in total Cd concentration.
Using rill/interrill comparisons to infer likely responses of erosion to slope length: implications for land management
Authors: Loch RJ
Published: April 2005

With the release of the Revised Universal Soil Loss Equation (RUSLE) there is potential to consider a range of responses of erosion to increasing slope length. This paper presents data to illustrate commonly observed effects of increasing overland flow on erosion processes and erosion rates, and considers the application of the data to specifying land management strategies and forms of vegetative cover most suited to particular soils. It also discusses a methodology for assessing relevant slope length factors for the RUSLE based on rill/interrill susceptibility. Three basic responses to slope length are noted: (i) little increase in erosion per unit area with increasing length, due to either the failure of rills to develop for the range of overland flows considered, or rill formation at very low hows with no further increase in erosion rates as flow rates increase; (ii) moderate increase in erosion per unit area with slope length associated with slight rill development; and (iii) large increases in erosion per unit area with slope length as rilling develops strongly. These responses have significance for the relative importance of surface and contact cover (and therefore, for the plant species grown and/or residue management strategy adopted), and for the use of contour banks to reduce slope length.
Soil solution composition and aggregate stability changes caused by long-term farming at four contrasting sites in South Australia
Authors: Naidu R , Mcclure S , Mckenzie NJ , Fitzpatrick RW
Published: April 2005

The effect of long-term farming on the cation exchange capacity (CEC), organic carbon content, soil solution composition, and aggregate stability was investigated using contrasting soils from 4 sites in the Mid North of South Australia. Undisturbed and farmed profiles were characterised at each site. Farming led to a 10–50% decrease, approximately, in organic matter and CEC in the surface horizon. Scanning electron microscopic study of the surface and selected subsurface soils revealed poor aggregation, compaction, reduced porosity, and a decrease in aggregate particle size in the farmed surface soils. Intra-aggregate binding in the undisturbed soils appeared to be largely due to fungal hypha, with the roots largely contributing to inter-aggregate binding of soil particles. Electrical conductivity (EC) of soil solutions was generally 2–3 times higher in the undisturbed soils than farmed soils, suggesting increased leaching of ions associated with loss of tree cover. This was also supported by a decrease in the concentrations of mobile ions such as Cl-and Na+ in the farmed soils. The concentrations of Na+ and K+ decreased with farming leading to a decrease in the Gapon selectivity constant for Na–Ca and K–Ca exchange. The changes in soil solution composition together with the decline in organic matter concentrations resulted in increased sensitivity of soils to dispersion.
Phosphorus retention and leachates from sandy soil amended with bauxite residue (red mud)
Authors: Summers RN , Smirk DD , Karafilis D
Published: April 2005

Bauxite residue (red mud) is a finely crushed, alkaline by-product of the alumina industry. The application of red mud to soil has the potential to reduce eutrophication of rivers and waterways by retaining nutrients on infertile sandy soils. The areas which may benefit from amendment with red mud are often groundwater recharge areas for drinking water and those near environmentally sensitive waterways, because of this, the off-site effects of red mud must be assessed before its widespread use. This research aimed to assess the length of time that phosphorus continued to be taken up by red mud and the best application rate of red mud to retain applied phosphorus. The effect of gypsum-amended red mud on phosphorus retention was examined. The composition of leachates from the red mud was compared with drinking water standards for humans and an untreated control. Monthly rainfall was simulated and leachate was collected from lysimeters filled with bleached grey sand amended with 5–80 t/ha of red mud, with and without gypsum. Leachates from over 12 months of simulated rainfall were tested for potential pollutants (Cd, Al, Fe, As, F, SO24-), electrical conductivity, pH, and P. The rainfall simulation was continued for the equivalent of 5 years and P levels were monitored during this time. The ionic concentrations of the leachates from columns treated with red mud were similar to the concentrations in the controls or fell to similar levels after the equivalent of 3 months of rainfall. The concentrations of these leachates were below the maximum recommended limits for drinking water, except in the case of fluoride which only occurred when gypsum was applied. The concentration of fluoride that leached from the gypsum-amended red mud dropped to drinking water standards within the equivalent of 7 months of rainfall. The best application rates of red mud which will reduce phosphorus leaching are 10–20 t/ha, without gypsum. The improved nutrient retention from red mud continues for the equivalent of at least 5 years of fertiliser application.
Effect of exogenous carbon on the sorption and movement of atrazine and 2,4-D by soils
Authors: Baskaran S , Bolan NS , Rahman A , Tillman RW
Published: April 2005

Sorption and movement of 2 ionic herbicides (2,4-D and atrazine) by 3 soil materials (Tokomaru silt loam, Egmont silt loam, mine tailings) which were amended with different levels of exogenous carbon (C) materials (poultry manure, sewage sludge, mushroom compost, peat, pig manure) were examined using 14C-labelled compounds. The sorption of herbicides was measured using a batch technique and the movement was examined using soil columns in which a pulse of 14C-labelled herbicide was leached with dissolved organic C (DOC). Sorption of herbicides, as measured by the distribution coefficient (Kd), increased with increasing C addition, and varied between the C sources. The difference in the effect of C sources on the sorption of herbicides was related to the difference in the amount of DOC and the pH. The increase in the Kd values per unit C addition decreased with increasing amounts of both the exogenous C addition and the indigenous C in the soil material. In a separate study, the addition of DOC to solutions of herbicides prior to sorption measurements decreased the sorption of herbicides, whereas the addition of DOC to soil increased the sorption of herbicides. Column studies have shown that DOC enhanced the movement of herbicides in soils. The effect of DOC on the movement of herbicides varied between the soil materials and may be related to the difference in the sorption of both the herbicides and the DOC.
Development of an automated double-ring infiltrometer
Authors: Maheshwari BL
Published: April 2005

A double-ring infiltrometer is often used for measuring infiltration characteristics in the field, but the measurements are time-consuming and tedious, especially when several tests are to be monitored at a site. This is because the infiltrometer in its present form requires continuous attention and therefore limits the number of tests that can be monitored at a site in a given time. An automated double-ring infiltrometer has been developed to overcome these limitations. It consists of inner and outer rings, water level sensors, water container, depth sensor, solenoid valves, 12-volt car battery, laptop computer, and software to perform recording and basic analysis of the infiltration data. The infiltrometer requires little attention once the test is started and the computer provides up-to-the-minute summary of infiltration results while the test is still in progress. The automated infiltrometer worked very satisfactorily during the field trials and has considerable potential as a research and teaching tool.
The distribution of potassium and sodium between the solution and the solid phase in a ternary (K–Na–Ca) system
Authors: Levy GJ , Feigenbaum S
Published: April 2005

Reduction of sodicity hazards in soils irrigated with waste water can be achieved through the replacement of the Na salts (mainly NaCl), used in water softening and other industrial processes, with potassium salts. We studied the effect of equilibrating a grumusol (Typic Chromoxerert) with solutions of differing potassium adsorption ratio (PAR) and sodium adsorption ratio (SAR), within the range expected in waste water, on the distribution of K and Na between the solution and the solid phase. The K distribution did not depend on the level of Na in the solution, but the distribution of Na between the 2 phases depended strongly on the PAR of the solution. For SAR 10 solutions, ESP decreased from 11.1 to 7.8 as PAR increased from 0 to 4. Gapon selectivity coefficients for Na, calculated separately for each PAR level, also decreased with increasing PAR. The Na distribution between solution and solid phase in a ternary (K–Na–Ca) system could not therefore be predicted from the Gapon selectivity coefficient obtained from a binary (Na–Ca) system.
Relationships between soil solution aluminium and extractable aluminium in some moderately acid New Zealand soils
Authors: Percival HJ , Giddens KM , Lee R , Whitton JS
Published: April 2005

This work investigates the relationship between soil solution aluminium (Al) and extractable Al in some New Zealand soils giving high extractable Al levels, yet with pH(H2O) values ≥ 5.2. Total Al in 1 M KCl extracts ranged from 0.8 to 11.6 cmol(+)/kg, and in corresponding 0.02 M CaCl2 extracts from 0.002 to 0.39 cmol(+)/kg. Soil solutions had low total Al concentrations, ranging from < 0.5 to 12.5 µM, with < 10% of the Al in the monomeric Al form as determined by the chromeazurol S colorimetric method. There was a poor correlation between Al in soil solution and that extracted by either 1 M KCl or 0.02 M CaCl2. The measured monomeric Al concentrations in the soil solutions did not exceed levels corresponding to Al toxicity threshold activities set at 10 or 2 µM, related to a range of pasture plant tolerances, whether based on the activity of Al3+ species alone, or on the sum of the individual activities of Al3+, Al(OH)2+ and Al(OH)2+ species. The high 1 M KCl-extractable and 0.02 M CaCl2-extractable Al values provided a misleading indication of potential Al toxicity status, probably due to the generation of artificially high extracted Al concentrations from these particular types of soils.
Interpretation of soil features produced by ancient and modern processes in degraded landscapes. VII. Water duration
Authors: Cox JW , Fritsch E , Fitzpatrick RW
Published: April 2005

Rising saline groundwater and fresh perched water have increased over 120 years (modern processes) in the Mediterranean region (>600 mm per annum) of the Mt Lofty Ranges, South Australia. This was caused by replacement of native vegetation with pastures which use less water. Relationships between morphological features (mainly soil colour) and field measurements (e.g. watertable duration, salinity, and sodicity) were studied to 3 m at 12 sites down a representative toposequence of red-yellow-grey duplex soils (Palexeralfs-Natraqualfs), which are common from crest to flat in these catchments. Three soil systems were identified from groupings of soil features: (i) brown/grey topsoil system (e.g. A and E horizons), (ii) red subsoil system (e.g. Bt), and (iii) yellow/white subsoil system (e.g. Btng or Cg). A water duration index was developed to quantify water duration in the brown/grey topsoil system from perched water levels measured in 12 dipwells installed to 0.5 m. Nested piezometers were used to determine if unsaturated zones occurred within the subsoil systems. Measured water duration and levels were compared with the presence pr absence of inferred redoximorphic features. Most features in the brown/grey topsoil system and the red and yellow/white subsoil systems reflected differences in water duration. A conceptual model was constructed to match successive changes in hydrology with differences in soil morphology and thus distinguish between modern and relict (late Mesozoic) soil features that developed under past and present hydrological conditions.
The dielectric behaviour of clay soils and its application to time domain reflectometry
Authors: Bridge BJ , Sabburg J , Habash KO , Ball JAR , Hancock NH
Published: April 2005

The dielectric behaviour of 3 soils, a sandy loam (Red Chromosol), a highly structured non-swelling clay (Red Ferrosol), and a self-mulching swelling clay (Black Vertosol), was investigated using a waveguide and network analyser technique in the frequency range 3.0 GHz to 4.5 GHz. Curves relating the real part of the relative permittivity to water content are presented and compared with the general Topp curve. The Chromosol generally followed the Topp curve, but the Ferrosol and Vertosol both had curves below the Topp curve. The Ferrosol showed a maximum horizontal offset of 0.05 m3/m3 from the Topp curve in the mid soil-water content range of 0.2–0.3 m3/m3 offset from the Topp curve of 0.10 m3/m3, with a maximum of 0.12 m3/m3 occurring at a soil water content of 0.4 m3/m3. Similar dielectric curves were obtained for the Chromosol and Vertosol using time domain reflectometry (TDR). With this method, the Chromosol showed very close agreement with the Topp curve, but the Vertosol again gave a curve below the Topp curve, similar to the one obtained using the waveguide and network analyser, but with a smaller maximum horizontal offset of 0.08 m3/m3. The difference between the waveguide and TDR Vertosol curves was mainly attributed to low bulk densities in the waveguide where packing was difficult. Some was also attributed to the wider spectrum of frequencies used by TDR. Use of the Topp curve for TDR measurements in the Vertosol would underestimate its water content by at least 0.06 m3/m3. These results are in good agreement with others obtained from similar soils. Deviations from the Topp curve are attributed to bound water associated with the clay particles and this depends on clay mineralogy and clay content. The presented calibration curves improve the accuracy of TDR measurements in these types of clay soils. A field comparison between water contents measured by TDR and gravimetric sampling in a similar Black Vertosol is presented. This calibration showed that soil water contents can be severely overestimated by using TDR with long probes and cables. This unexpected and opposite result is discussed in terms of attenuated high frequencies in the 15-m-long connecting cable used, errors in depth of probe placement, and changes in bulk density and DC conductivity.