bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-term net N mineralization from plant residues and gross and net N mineralization From soil organic-matter after rewetting of a seasonally dry soil
Authors: Sparling GP , Murphy DV , Thompson RB , Fillery IRP
Published: April 2005

The mineralization of N from shoot residues of two legume species and a common weed component of Western Australian pastures was measured after a simulated 'summer rainfall' in a laboratory experiment using undisturbed soil cores of a loamy sand. Water was added to the surface of the cores equivalent to a single rainfall event of 10 mm water (treatment 1); or followed 48 h later by a further application of 10 mol water (treatment 2). Net mineralization and microbial biomass N were measured over 144 h following the initial rewetting of the soil cores. Three types of 15N-labelled plant residue, namely (i) lupin leaf (Lupinus angustifolium), (ii) clover (Trifolium subterraneum) shoot, burr and petiole, and (iii) capeweed (Arctotheca calendula) shoots and leaves were placed on the soil surface as large fragments and examined to assess their mineralization and incorporation into microbial biomass. The soils dried rapidly after rewetting and net mineralization of N was very low. The proportion of N as nitrate was increased in the rewetted soils with the major changes occurring in the top 5 cm of soil. However, there was very little mineralization of the surface-applied plant residues, with more than 90% of the mineral N being derived from the native organic matter. Microbial biomass showed fluctuations in both the rewetted treatments, but no consistent increase or decrease and no significant immobilization of 15N. Gross N mineralization was measured using an isotopic dilution technique involving the injection of 15N-labelled solutions into the soil. Estimates of gross N mineralization after a single rainfall event of 10 mm water were, on average, four times greater than measures of net N mineralization. Gross N mineralization rates declined as the soil dried, with three times more mineralization occurring in the 0-5 cm depth (4.73-8.93 �g g-1 day-1), compared with the 5-10 cm depth (0.86-2.38 �g g-1 day-1). A major disadvantage with the isotopic dilution method was that injection of the solutions into soil greatly increased the soil moisture content. Gross mineralization in the injected cores is likely to have been overestimated because of N movement below the sampling zone and increased microbial activity relative to non-injected cores.
Influence of cropping on the population of a native earthworm and consequent effects on hydraulic properties of vertisols
Authors: Friend JJ , Chan KY
Published: April 2005

Population density of Heteroporodrilus mediterreus, a large native earthworm found on the Mitchell grassland (Astrebla lappacea) on the Vertisol plains near Walgett, New South Wales, was investigated at two sites (brown and grey clays). Maximum earthworm activity at the soil surface layer was observed during winter (July/August) corresponding to more favourable soil moisture conditions. The highest earthworm population density (7.5 m-2) and biomass (0.89 t ha-1) were detected at the brown clay site under natural pasture. Populations were much lower (by two thirds in the brown clay) and the proportion of immature worms was much higher in the cropped soils than in the pasture soils. Current wheat cropping practices involving long fallowing and excessive cultivation during the period when earthworms are active at the surface are the possible causes of the reduction in population. Disc permeameter measurements compared with infiltration through single earthworm holes showed that the earthworm channels contributed significantly to the movement of water into the subsoil. Their persistence under wet conditions, even after closure of shrinkage cracks, suggests they are also important in maintaining subsoil aeration. Significant reductions in sorptivity and infiltration rate were observed in the cropped soils.
Polymer molecular-weight and degree of drying effects on infiltration and erosion of three different soils
Authors: Levy GJ , Agassi M
Published: April 2005

Low infiltration rate and high levels of soil erosion are critical problems in many soils worldwide. Amendment of soils with organic polymers could alleviate these problems. The objective of the present study is to investigate the effects of polymer molecular weight and the degree of drying on the infiltration rate of, and erosion from, three different soil types from Israel. A solution of high-molecular-weight (2x107 Da) or low-molecular-weight (2x105 Da) negatively charged polyacrylamide (PAMH and PAML, respectively) was added to the surface of soil samples packed in trays, at a rate of 20 kg ha-1. The soil samples were allowed to dry to varying degrees and were then exposed to 60 mm of simulated rain during which infiltration rate and soil loss were determined. The ability of the polymer to maintain high final infiltration rates (FIR) depended on its molecular weight and the clay content of the soils. In the coarse- and medium-textured soils, the PAMH was more effective than the PAML in maintaining high FIR. In the fine-textured soil, the effects of both polymers on Fm. were comparable; the use of the PAML is therefore preferable since it is easier to handle. Both polymers had reduced soil loss comparably. The effects of drying were similar for both polymers: the FIR and soil loss values with the intermediate degrees of drying were higher and lower, respectively, than they were with the no-drying or complete-drying treatments.
A field-study of leaching and degradation of nine pesticides in a sandy soil
Authors: Kookana RS , Di HJ , Aylmore LAG
Published: April 2005

A field study was conducted on a coastal sandy soil (Karrakata sand) of Western Australia from July to December 1990, to measure the leaching and degradation rates of chlorpyriphos, chlorthal dimethyl, fenamiphos, linuron, metalaxyl, metribuzin, prometryne, propyzamide and simazine. Commercial grade products were sprayed in dilute solution form at recommended rates to the surface of held plots. Irrigation was applied daily which together with rainfall gave effective rainfall equivalent to at least 120% of potential evaporation. Pesticide residue concentrations in soil samples taken at 5 cm increments down to 50 cm, at different days after application, were determined by high performance liquid chromatography (HPLC). Mean leaching depths (MLDs) were calculated by weighting the percentage residues remaining at different depths in the soil profile. The MLDs for the 5 month period followed the order: chlorpyriphos and chlorthal dimethyl (<5 cm) < linuron and simazine (6) < propyzamide (8) and prometryne (9) < metribuzin (12) < metalaxyl (18) < fenamiphos and metabolites (28). This generally corresponded inversely with the sorption coefficients (K-oc). The degradation rates (i.e. decreases with time of total residue concentration in the sampled profile) could mostly be described by first-order regressions (R(2) = 0.59-0.95). Calculated half-lives showed the order: metribuzin (27 days), simazine (28) < fenamiphos (43), chlorthal dimethyl (45) < prometryne (58), propyzamide (59) < metalaxyl (70) < chlorpyriphos (81) < fenamiphos plus metabolites (98) < linuron (219). The potential for causing ground water contamination, as indicated by the ratio of half-life to Koc followed the order: chlorthal dimethyl, chlorpyriphos < metribuzin, prometryne < simazine, propyzamide < linuron < metalaxyl < fenamiphos and metabolites.
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.
Soil management and production of alfisols in the semi-arid tropics. III.* Long-term effects on water conservation and production
Authors: Cogle AL , Littleboy M , Rao KPC , Smith GD , Yule DF
Published: April 2005

A calibrated cropping systems model was used to provide long-term biophysical responses of various land managements at two differing semi-arid tropic environments in India. Organic based practices such as farmyard manure or straw amendments and perennial pastures reduced runoff by between 50 and 87%, and are optimum for in situ, water and soil conservation. A consequence of the reduced runoff was an increase in drainage below the root zone. Furthermore, the detrimental effects of cropping on high slopes and long slope lengths showed that it is not feasible to crop on slopes greater than 5%. Our study did not incorporate farmer preferences for land management, but the results can still be used as an integral part of decision making for optimum land management.* Part II, Aust. J. Soil Res. 1996, 34, 103–111.
A double-puncture technique for improving the accuracy of puncture tensiometer measurements
Authors: Greenwood KL , Daniel H
Published: April 2005

Measurements taken with a puncture tensiometer are biased due to the small positive pressure exerted on the system when the syringe needle is inserted into the air space at the top of the tensiometer. An equation based on Boyle's Law, relating two successive measurements from puncture tensiometers to the initial tension, was developed to correct this problem. The initial tension, T0, inside the puncture tensiometer can be calculated from T21/ T2 where T is the tension inside the puncture tensiometer and the subscripts 1 and 2 refer to the first and second readings taken with the puncture tensiometer meter. Laboratory testing at tensions of 5, 10, 20 and 40 kPa showed that average results from this double-puncture technique were within 0.2 kPa of the actual tension. All results using this technique were accurate to 6%. In contrast, the average tension calculated from the single-puncture tensiometer readings underestimated the actual tension by up to 2.3 kPa and the maximum errors were approximately 10%. Use of the double-puncture technique will improve puncture tensiometer measurements in the field without the need to wait for re-equilibration of the pressure or application of calibration equations.
Pans in humus podzols (Humods and Aquods) in coastal southern Queensland
Authors: Thompson CH , Bridges EM , Jenkins DA
Published: April 2005

An exploratory examination has been made of three different kinds of hardpans found in humus podzols (Humods and Aquods) of the coastal lowlands of southern Queensland, by means of slaking tests, a reactive aluminium test, acid oxalate and pyrophosphate extractions and electron microscopy. Samples from three indurated layers exposed by erosion or sand-mining in large coastal dunes were included for comparison. The investigation confirmed that, a pan in a bleached A2 (albic E) horizon is most likely caused by particle packing and that a pan in a black B2h (spodic) horizon is cemented by an aluminium-organic complex. Yellow-brown pans underlying black organic pans (spodic horizons) were found to be cemented by both a proto-imogolite/allophane complex and an organic substance. An inorganic reactive Al complex differing from the proto-imogolite allophane recorded in the overlying giant podzols appeared to be main cement of three indurated layers in the nearby coastal sand dunes. Mechanical disturbance of the pans, e.g. ripping, is unlikely to improve drainage and effective soil depth in the long term, because the disturbed zones are expected to be re-sealed by packed particles or by the aluminium-organic complex cement.
Effects of high pH solutions with large monovalent cation concentrations on cation exchange properties
Authors: Liefering RE , Mclay CDA
Published: April 2005

Disposal of strongly alkaline industrial liquid wastes, which contain large monovalent cation concentrations, by means of land treatment systems is becoming increasingly common. This study investigated the effects of solutions with large monovalent cation concentrations and high pH on cation exchange properties in four New Zealand soils with different clay mineralogies. The soils were shaken with a range of concentrations (0–0.3 M) of NaOH, KOH, NaCl, and KCl. Cation exchange capacity (CEC) and exchangeable cations (Ca2+, Mg2+, K+, and Na+) were measured following shaking and washing procedures. Although the hydroxide solutions dissolved significant amounts of organic matter from all soils, there was still a net increase in CEC measured at all hydroxide concentrations. The magnitude of the CEC increase was dependent on hydroxide concentration. The increase in CEC is attributed to newly generated negative charge on surfaces which possess variable charge (i.e. pH dependent) characteristics such as edge sites of clay minerals, sesquioxides, and the undissolved organic matter remaining in the soil. In contrast to hydroxide solutions, no increase in CEC was measured in chloride-treated samples. Increases in the concentration of all treatment solutions resulted in increases in the exchangeable ion concentration of the index cation used in the treatment solution (either Na+ or K+) and decreases in concentration of the other three exchangeable cations. In general, higher exchangeable sodium percentage (ESP) values were measured in samples treated with NaOH than samples treated with NaCl at all concentrations. Similarly, higher exchangeable potassium percentage (EPP) was measured in samples treated with KOH than samples treated with KCl at all concentrations. The higher ESP and EPP values recorded when hydroxide solutions were used as treatments are attributed to the newly generated negative charges being counter-balanced by the monovalent index cation present in the treatment solution. It is suggested that existing equations commonly used to predict ESP and EPP values are unsuccessful for accurately predicting changes when soils are treated with hydroxide solutions, due to their inability to account for the newly generated exchange sites. The equations did, however, adequately predict the effects of both chloride solutions on ESP and EPP.
Comparison of legume-based cropping systems at Warra, Queensland. 1. Soil nitrogen and organic carbon accretion and potentially mineralisable nitrogen
Authors: Hossain SA , Dalal RC , Waring SA , Strong WM , Weston EJ
Published: April 2005

Effects on soil nitrogen accretion and potentially mineralisable nitrogen were studied as part of a long-term field experiment established in 1986 to test alternative legume-based systems for restoring fertility in a Vertisol. Organic C accretion was also measured to ascertain the changes in organic matter content. The systems, which were studied only during 1989 and 1990, were a grass+legume ley (purple pigeon grass, Rhodes grass, lucerne, annual medics) of 4 years duration followed by wheat; a 2-year rotation of wheat (lucerne undersown) and lucerne; a 2-year rotation of wheat (medic undersown) and medic; a 2-year rotation of chickpea and wheat; and continuous wheat as control. Soil total N and organic C significantly increased in the 0–10 cm soil layer only under the grass+legume ley. There was no significant change in the soil C/N ratio. Plant residues contained from 52 to 104 kg N/ha in 1990 at the end of the legume phase, with high values for root N in the grass+legume ley. A comparison of N accretion versus fixation at the end of the legume-based systems in 1990 showed that net accumulation of N exceeded fixation in soil under lucerne and grass+legume leys; in the latter, net accumulation of 779 kg N/ha over 3.75 years was measured compared with 384 kg N/ha for N2 fixation. Part of the accumulation of N may have been due to uptake of NH4-N from the deep subsoil. Although values for soil mineral N (0–120 cm) were low at the end of all the legume-based systems, a deep subsoil (120–300 cm) accumulation of NH4-N was found in all treatments. The nitrogen mineralisation potentials (No) for 0–10 cm depth samples taken at the end of the legume phase in 1989 were higher in all the legume-based systems (105–182 mg N/kg) than the wheat control (57 mg N/kg). The rapid biological tests of N availability, both waterlogged and aerobic incubation, were more sensitive to treatment differences than No, in the surface and subsoil (range 12–78 mg N/kg for 0–10 cm soil for the waterlogged procedure). The rapid chemical tests, hot KCl extraction and the autoclave index, showed small treatment effects and did not appear to be useful availability indices. The pasture management (graced v. mown and removed) had no significant effect on total N, organic C and N availability indices in this alkaline Vertisol during the study period.
Effects of conservation tillage and rotation on water infiltration in two soils in south-eastern Australia
Authors: Bissett MJ , Oleary GJ
Published: April 2005

The infiltration of water under long-term (8–10 years) conservation tillage (zero and subsurface tillage with stubble retention) and conventional tillage (frequent tined tillage with no surface residues) systems was compared on a grey cracking clay and a sandy loam soil in south-eastern Australia. Potential infiltration rates were higher under conservation tillage on both soil types. On the grey clay soil, stubble retention and zero tillage produced up to an 8-fold increase (from 12–33 to 145–206 mm/h) in saturated hydraulic conductivity (Ks) compared with the conventional practice of removing stubble by burning or grazing, followed by frequent tillage to control weeds. An annual application of nitrogen at 20–60 kg/ha had no significant effect on Ks. Similarly, on the sandy loam soil a 2-fold increase in Ks was observed from conservation tillage. Increases in Ks from approximately 46 to 96 mm/h occurred in rotations which included an 18-month fallow with conservation tillage (stubble retention and zero tillage) compared with conventional tillage (stubble removed and frequent tillage). A continuous rotation of pasture and wheat under conventional tillage had a significantly lower Ks of 22–23 mm/h which was increased to 47–49 mm/h with stubble retention and zero tillage. These differences in Ks explain an important mechanism for increased water storage on these soil types under reduced tillage.
Soil friability in relation to management history and suitability for direct drilling
Authors: Macks SP , Murphy BW , Cresswell HP , Koen TB
Published: April 2005

Friability was determined for a selection of soils from the southern wheatbelt of New South Wales. Samples were taken from the surface of a range of soils that included a red-brown earth, a red earth, and a non-calcic brown soil, and covered a range of management histories. Differences in soil management history explained most of the variation in friability. Uncultivated woodland soils were highly friable in the top 20 mm [mean friability index (k) = 0.66], with intensively tilled soil the least friable (mean k = 0.05). Soils under direct drilling (DD) had friability similar to that from woodland sites (mean k = 0.55). Intensive cultivation of hardsetting soils over a number of seasons decreased their friability. Aggregates of 50 mm effective diameter had tensile strengths that ranged from 18 to 1087 kPa at woodland and DD sites, while the tensile strengths for the same size aggregates of soils under traditional tillage (TT) were between 1061 and 4419 kPa. Aggregates of 2 mm diameter had tensile strengths of 17 884–63 432 kPa for woodland and DD soils, and 2012–5268 kPa for TT soil. Significant relationships were detected between friability and the tensile strength of aggregates of 2, 20 and 50 mm size and this might present an easier means of determining friability. Friability was found to be significantly related to a number of other soil structural properties, including hydraulic conductivity, bulk density, organic carbon, aggregate stability, and sorptivity. Friability might be a useful indicator of the suitability of soil structural condition for crop establishment by direct drilling. Soils with low friability appear difficult to direct drill successfully; this reduces the management options available for their amelioration. Further work is necessary to relate friability directly to seedbed conditions following direct drilling and subsequent plant emergence and growth, and to establish firmly the wider applicability of relationships between friability and other soil structural properties.
Zinc speciation in soil solutions of Vertisols
Authors: Dang YP , Tiller KG , Dalal RC , Edwards DG
Published: April 2005

Soil solutions were obtained by a centrifugation method from 14 unfertilised and fertilised Vertisols. The soil solutions were analysed for all major cations and anions and organic carbon (C). Chemical speciation of zinc (Zn) in the soil solutions calculated with the aid of the computer program GEOCHEM showed that Zn in tile soil solution exists mainly as free Zn2+ ions in these soils. Complexation of total soluble Zn by organic and inorganic ligands constituted 40% and 50%, respectively, of total soluble Zn in fertilised and unfertilised soil solutions. The organo-Zn complexes constituted <10% of the total soluble Zn. The inorganic Zn complexes, ZnHCO3+ and ZnCO3, constituted 60–75% of the total inorganic Zn complexes. The Zn complexes with SO24- and OH- were less than or equal to 5% each of the total inorganic species in unfertilised soils; ZnSOo4 complexes were more common in fertilised soils. The activities of Zn were extremely low (0.01–0.1 µM) in unfertilised soils and were inversely related to soil solution pH. The experimentally determined solubility lines for Zn2+ in the soil solution were undersaturated with respect to the solubility of any known mineral form of Zn. Zn2+ activity was mainly determined by adsorption-desorption reactions. The weak acid ion exchangers, Chelex-100 and Bio Rex-70, retained smaller amounts of Zn front the soil solutions than the strong acid exchangers, AG 50W X2, AG 50W X4, and AG 50w X8. Soil solution pH strongly affected Zn concentrations in soil solutions. The amount of total soluble Zn present as Zn2+ ions as calculated by GEOCHEM was highly correlated with tile amount of soluble Zn retained by the cation exchange resins. In the case of Chelex-100, these amounts were equal, confirming the usefulness of Chelex-100 to estimate Zn2+ ions.
The influence of inorganic matrices on the decomposition of straw
Authors: Skene TM , Skjemstad JO , Oades JM , Clarke PJ
Published: April 2005

The decomposition of straw (St) in the absence or presence of inorganic matrices [sand (S), sand+kaolin (S+K), loamy sand (LS)] with and without added N (in the form of urea) was followed by chemical and spectroscopic methods over 24 weeks. Inorganic matrices had a significant effect on C mineralisation from day 14 onwards, and at the end of the incubation (day 168), the relative proportion of C remaining was least in the St+S+K+N, St+S+N and St+S-N treatments, and most in the St+LS+N and St+LS-N treatments. The LS and S+K matrices partially inhibited mineralisation, possibly by physical protection of the straw, but the addition of N to the S+K matrix negated this effect. Added N increased the mineralisation of C during the first 5 weeks but had little effect after this time. The addition of N increased the rate of change of the C : N ratio for the St+LS+N treatment in the first 16 weeks but did not significantly influence tile rate of change for the other treatments. When all the treatments were compared, inorganic matrices only had a significant effect on C : N ratios in the first 6 weeks of the incubation; however, if only the -N and +N treatments were compared, there were significant differences between inorganic matrices throughout tile incubation. For the -N and +N treatments, the St+LS-N and St+N treatments had the lowest C : N ratios at day 168, respectively. Treatments with straw only had biomass C concentrations an order of magnitude higher than those of the inorganic matrix treatments. However, when biomass C was expressed as a proportion of total organic C, the St+S+K+N treatment was significantly higher than all other treatments, suggesting that clay was protecting the microbial biomass against predation by other organisms. Solid state 13C CP/MAS NMR spectra of whole samples from each treatment al the end of the incubation suggested that straw incubated in inorganic matrices was more decomposed (as determined by the O-alkyl-C : alkyl-C ratio) than the straw only treatments, despite the occurrence of the same amount of, or less, mineralisation. Either there are differences in the decomposition/mineralisation balance between treatments or alkyl-C has been synthesised by the microbial biomass and preserved by the inorganic matrices. Examination of the alkyl-C region of the various spectra suggests that the alkyl-C which persists in the inorganic matrices is both plant and microbially derived; hence the latter explanation is probably true.
Measurement of plant-available cadmium in New Zealand soils
Authors: Andrews P , Town RM , Hedley MJ , Loganathan P
Published: April 2005

Several methods of measuring plant-available cadmium (Cd) were compared using soils that had accumulated Cd under normal New Zealand agricultural practices (low total Cd concentrations, and phosphatic fertiliser as the dominant Cd source). The study encompassed 9 New Zealand soils with different Cd input histories. Cadmium was extracted from these soils by demineralised water, 0.05 M Na2EDTA, 1 M NH4OAC (pH 7), 0.01 M CaCl2, and 0.05 M CaCl2 and quantified by differential pulse anodic stripping voltammetry (DP-ASV) and graphite furnace atomic absorption spectrophotometry (AAS). The DP-ASV measures the free Cd ion and that associated with labile complexes, but not large organic Cd complexes. Extractable Cd levels were compared with those which are plant-available, as determined by pot studies (lettuce). The 0.01 M CaCl2-extractable Cd measured by AAS and 0.05 M CaCl2-extractable Cd measured by DP-ASV gave the best estimate of plant availability of Cd.
Water repellency and its role in forming preferred flow paths in soils
Authors: Ritsema CJ , Dekker LW
Published: April 2005

The role of water repellency in forming preferred how paths, and in accelerating solute transport, is explained on the basis of extensive field measurements in a grass-covered, extremely water-repellent sandy soil in the coastal region of the Netherlands. It was shown that following wetting of the 9-cm-thick humous topsoil to around 20–25 vol.%, preferred how paths, or fingers, were formed in the sandy subsoil. The fingers started at the layer interface at 'weak' spots with a relatively low degree of potential water repellency, and protruded vertically into the sandy subsoil. Flow through the fingers caused water-repellent substances to be leached from the topsoil to the subsoil, progressively fixating the finger positions. Laboratory analysis revealed that wetting of dry, water-repellent soil between the vertically directed fingers is an extremely slow process compared with wetting of dry, non-water-repellent, or slightly water-repellent, soil. Evidence was presented that fingers at the field site disappeared during dry periods and recurred at the same location during new rain events. Vertical solute leaching down the fingers was greater by a factor of 3 than that estimated on a piston flow basis. The development of new simulation models capable of predicting water and solute transport through water-repellent soils is urgently needed.
Potentiometric determination of total nitrogen in soils by flow injection analysis with a gas-diffusion unit
Authors: Ferreira AMR , Lima J , Rangel A
Published: April 2005

A flow injection analysis (FIA) system incorporating a gas-diffusion unit and a potentiometric detector was developed for the determination of total nitrogen in soil digests. The solutions obtained from the Kjeldahl digestion of the soil samples were injected in the FIA system where ammonium was converted into ammonia. This gas diffused through a gas-permeable membrane to a buffer acceptor stream, allowing the separation of the gas from the rest of the sample. Once in contact with the buffer solution, ammonia was reconverted into ammonium and finally led to a tubular ammonium ion-selective electrode constructed for this purpose. The potentiometric detector is a PVC tubular selective electrode without inner reference solution, and with the sensor system composed of monactin in Tris (2-ethylhexyl) phosphate. Good agreement was obtained between the results provided with the developed FIA system and those from the classical Kjeldahl distillation/titration step, with relative deviations between the 2 methods always < 5%. A sampling rate of 80 determinations/h was achieved with good reproducibility for consecutive injections of soil digests (coefficients of variation < 3%).
Relationships between three measures of organic matter or carbon in soils of eucalypt plantations in Tasmania
Authors: Wang XJ , Smethurst PJ , Herbert AM
Published: April 2005

Organic carbon or organic matter in acidic Tasmanian soils supporting eucalypt plantations was measured by dry combustion using a LECO CHIN-1000 Analyzer (CT), wet oxidation by the Walkley-Black method (CW&B), and loss-on-ignition (LOI at 375°C). CT and CW&B were highly correlated in 119 surface and subsoil samples, and on average, CW&B provided near complete recovery of CT (97%). Although LOI may have released some structural water from the fine-textured soils, and apart from granite-derived soils which need further study, strong regressions were found between LOI and both CW&B and CT which were specific for either basalt or non-basalt soils. Within the non-basalt soils, parent material had little effect on these relationships, although there were large differences in C concentrations of surface soils between soils of different parent materials. The relationships of CW&B and CT to LOI in the basalt soils were significantly different from those in the non-basalt soils.
Bauxite residue (red mud) improves pasture growth on sandy soils in Western Australia
Authors: Summers RN , Guise NR , Smirk DD , Summers KJ
Published: April 2005

Red mud is a finely crushed, iron-rich, alkaline residue, obtained by digesting bauxite with caustic soda to remove the alumina. The remnant alkalinity of red mud is equivalent to 11% pure calcium carbonate. Phosphorus leaching from infertile sandy soils has resulted in eutrophication of estuaries and has caused algal blooms. Red mud has been shown to reduce leaching of phosphorus from sandy soil. This research was undertaken to determine the effect of red mud on pasture growth and uptake of heavy metals. Red mud, either untreated or treated with gypsum, was applied at rates of 0, 10, 20, 40, and 80 t/ha to a subterranean clover and ryegrass hay paddock. There were 3 replicates of each treatment and a completely randomised design was used. The experimental design was 5 rates of red mud x 2 untreated and treated with gypsum x 3 replicates, resulting in 30 plots. Plant growth, and nutrient and heavy metal composition of the plant tops, were measured. An application of 40 t/ha of red mud increased hay (mainly subterranean clover and ryegrass) production by 24% and increased soil pH in the top 10 cm by 1.0 unit from 3.5 (1 : 5 soil : 0.1 M CaCl2). The increase in production was probably because of the liming effect of the remnant alkali in the red mud, which may have potential as a replacement for crushed limestone. Sodium carbonate, the predominant alkali in red mud, is more soluble than calcium carbonate from crushed limestone and has the potential to change the pH of the soil more rapidly. The soil was top-dressed with red mud, without disturbing the existing pasture, resulting in changes to the pasture production and nutrient composition consistent with a change in soil pH throughout the rooting depth. If crushed limestone is not mixed into the soil it may take many years to increase the pH of the soil; however, this mixing results in extra cost from re-seeding and an initial depression in yield. Although much more red mud is needed than lime, the cost is comparable when the haulage distance is less than about 30 km. In previous trials, at red mud application rates > 500 t/ha, gypsum was mixed into the red mud to reduce salinity and pH. At these rates, the red mud had overwhelmed the buffering capacity of the soil. The gypsum reduced the pH by changing the sodium carbonate in the red mud to calcium carbonate, thus changing the pH from > 10 to about 8.5. However, amendment of the red mud with gypsum when applied at rates < 80 t/ha proved unnecessary in this experiment, probably because the proportion of soil was sufficient to alter the pH of the red mud. When red mud is applied to acidic infertile sands, manganese application as manganese sulfate may be necessary, because the rise in pH may rapidly induce manganese deficiency in plants. Care should be taken to monitor other nutrients which have their availability for plants affected by pH (e.g. copper, zinc, and molybdenum). Red mud did not elevate the concentrations of heavy metals in the soil, hay, or fresh plant tissue.
Leaching of copper, chromium, and arsenic through some free-draining New Zealand soils
Authors: Carey PL , Mclaren RG , Cameron KC , Sedcole JR
Published: April 2005

Concentrated toxic solutions of copper, chromium, and arsenic (CCA) are used extensively in the New Zealand timber preservation industry. A 2% w/v solution containing cupric, dichromate, and arsenate ions was leached through undisturbed soil monolith lysimeters containing the surface and subsurface horizons of 2 free-draining New Zealand soils. The resulting breakthrough curves were successfully modelled using the Gompertz equation for biomass growth. Differences between soil horizons in the fitted Gompertz parameter values were related to differences in soil physical and chemical properties affecting leaching. Results were compared to those from a previous study investigating pulse leaching of a concentrated CCA solution of similar ion ratio using the same soils. Generally, solution leaching produced breakthrough curves influenced more by the soil's physical structure and less by kinetic processes (i.e. sorption and diffusion). This was in part due to the high metal concentrations of the CCA solution and the decreased contact time between soil and solute in the solution leaching experiment. The relative ease of solute ion breakthrough increased in the order copper < arsenate < dichromate. The study suggests that further research is required to assess management implications for spills of these heavy metal ions to soils to prevent leaching or runoff to ground and surface water.
Iron-manganese nodules in a semi-arid environment
Authors: Sanz A , Garcia-Gonzalez MT , Vizcayno C , Rodriguez R
Published: April 2005

Relationships between the chemical, mineralogical, and morphological characteristics and the formation mechanisms of some iron-manganese (Fe–Mn) accumulations were investigated. The nodules studied were from a poorly drained soil profile with a high calcium carbonate content, located in a semi-arid environment. Three types of nodules, Fe-rich (typic or annular morphology) Mn-rich (aggregate morphology), and Fe–Mn-rich (compound morphology), were encountered, all of which were formed in situ. The nodules were found to contain goethite, and a low proportion of poorly crystallised Fe oxides and Mn oxides (birnessite and vernadite). However, they contained no siderite or rhodochrosite, both highly frequent occurrences in carbonatic systems with redox fluctuations. In the formation of compound nodules, Fe- and Mn-rich nodules may act as nucleating structures for subsequent accumulations in the form of coatings and/or matrix impregnations.
Occurrence of talc in soils with high iron content from the south-west of Spain
Authors: Perez-Rodriguez JL , Maqueda C , Rodriguezrubio P , Deharo MCJ
Published: April 2005

The mineralogy of the clay fractions of 2 soil profiles classified as an Alfic Dystric Eutrochrept (Soil I) and a Xerochreptic Haploxeralf (Soil II) has been determined. A notable feature of these soils is the presence of talc and the high iron content as goethite, hematite, lepidocrocite, and maghemite. Talc was the most abundant non-iron mineral of the clay fraction of Soil II. In Soil I, talc occurs as a residual phase from the parent material with its persistence in the profile aided by coatings of iron oxides, which inhibit further weathering. In these soils there is a high proportion of goethite accompanied by hematite. In Soil I the proportion of iron oxides changes within the profile. Another notable feature of this profile is the presence of maghemite in the upper horizons where this is the predominant iron oxide mineral.
A soil fractionation related to soil structural behaviour
Authors: Colleuille H , Braudeau E
Published: April 2005

To date, in order to characterise and understand soil behaviour, most emphasis has been placed on surrogate measurements of soil structure. However, a direct assessment of the structure of well-aggregated (pedal) soil samples can provide relevant information on soil organisation and lead to a better understanding of soil behaviour. In this paper, we suggest an original fractionation allowing natural soil structural elements, defined on morphological criteria and related to soil behaviour, to be separated. The soil samples come from 2 tropical sequences widespread in the intertropical zone: a ferrallitic and ferruginous soil sequence from Basse-Casamance (Senegal); and an alluvial soil sequence from the middle valley of the Senegal River. The principle of the fractionation is based on the concept of soil friability, and on the use of an organic solvent to separate primary structural units of soil samples first equilibrated at a specific soil water potential. This optimal soil water potential is selected on the basis of experimental studies and its relevance is discussed in relation to the particular structural properties of the soil occurring at this wetness.
The relation between soil water retention and particle size distribution parameters for some predominantly sandy Western Australian soils
Authors: Smettem KRJ , Gregory PJ
Published: April 2005

The soil water retention curve (WRC) may be estimated from soil texture if there is shape similarity between the normalised cumulative particle mass size distribution curve (PSD) and the WRC. For similar shaped curves, parameters describing the shape of the PSD may also describe the shape of the corresponding WRC. We studied the relation between PSDs and WRCs at 4 sites in Western Australia with predominantly sandy soils and fitted a sigmoidal function to all normalised PSDs and WRCs. The model gave an excellent description of all PSD and WRC data sets. The parameter describing the slope of the WRC was correlated with the slope of the PSD. However, the asymptotic minima of the PSDs differed from the WRCs leading to poor estimates of the WRC residual water contents, θr. This difference was most marked in 2 clay subsoils and resulted in progressively greater errors in prediction of water content with increasing negative pressure head.
Method-induced variations in soil erodibility in erosion experiments with rain-impacted flow
Authors: Kinnell PIA , Ramos MC , Uson A
Published: April 2005

Laboratory experiments on erosion by rain-impacted flow were performed on crusted surfaces that had either been eroded or not been eroded previously by rain-impacted flow. Differences in the erodibility of the surfaces were obtained between the 2 methods. The differences in erodibility were associated with the development of a layer of coarse pre-detached material on the previously eroded surfaces. The influence of this layer on erodibility is such that changing the experimental procedure may influence the results obtained from experiments designed to determine soil erodibility under rain-impacted flow.
Rainfall erosivity estimation using daily rainfall amounts for South Australia
Authors: Yu B , Rosewell CJ
Published: April 2005

The rainfall erosivity model relating storm erosivity to daily rainfall amounts was tested for 4 sites in South Australia where seasonal rainfall erosivity is generally out of phase with seasonal rainfall because of the predominant winter rainfall. The model worked reasonably well, with the coefficient of efficiency varying from 0.54 to 0.77, and the average discrepancy between actual and estimated monthly distribution was no more than 3%. The model performance in the winter rainfall area is similar to that in the uniform and summer rainfall areas. A set of regional parameter values estimated using a combined dataset is recommended for other sites in the agricultural and viticultural areas of South Australia where the mean annual rainfall ranges from 300 to 500 mm. The R-factor and its seasonal distribution were estimated for 99 sites in South Australia using long-term daily rainfall data. The R-factor varies mostly between 250 and 500 MJ . mm/(ha . h . year). Rainfall erosivity peaks in winter in the southern part of the western agricultural area and the south-east corner of the State, while it peaks in summer in the inland area east of the South Flinders and Mount Lofty Ranges.
Concentrations of rare earth elements in some Australian soils
Authors: Diatloff E , Asher CJ , Smith FW
Published: April 2005

Total, exchangeable, and soil solution concentrations were measured for 15 rare earth elements (REEs) in 9 soils from Queensland and New South Wales. In a further 10 acid soils, effects of amendment with CaCO3 or CaSO4 . 2H2O were measured on the concentrations of REEs in soil solution. The total concentration of the REEs in soil solutions from unamended soils ranged from below the detection limit (0.007 µM) to 0.64 µM. Lanthanum (La) and cerium (Ce) were the REEs present in the greatest concentrations, the highest concentrations measured in the diverse suite of soils being 0.13 µM La and 0.51 µM Ce. Rare earth elements with higher atomic numbers were present in very low concentrations. Exchangeable REEs accounted for 0.07 to 12.6% of the total REEs measured in the soils. Addition of CaCO3 increased soil solution pH and decreased REE concentrations in soil solution, whilst CaSO4 . 2H2O decreased soil solution pH and increased the concentrations of REEs in soil solution. Solubility calculations suggest that CePO4 may be the phase controlling the concentration of Ce in soil solution.
Nitrogen mineralisation and its error of estimation under field conditions related to the light-fraction soil organic matter
Authors: Sierra J
Published: April 2005

In situ, incubations of intact soil cores were carried out to identify factors controlling nitrogen (N) mineralisation and its spatial variability under field conditions. The analysed factors were soil moisture, temperature, and the content of light-fraction (density ≤ 2 Mg/m3) organic carbon (LC) contained in the soil. The error associated with the estimate of in situ N mineralisation was analysed using undisturbed samples in laboratory incubations. The coefficient of variation of in situ N mineralisation ranged from 58 to 234%. Nitrogen and LC mineralisation in the field showed a similar temporal pattern. The major factor affecting this pattern was soil temperature, soil moisture being near the optimum level throughout the experiment. The rate of N mineralisation during an incubation period was correlated with the content of LC at the beginning of the period; this factor explained 40–50% of the variation in N mineralisation. At a low rate of N mineralisation, a large proportion of the spatial variability was attributed to the error of estimation. From the relationship between N mineralisation and LC content, we estimated the rate constant k which could be expressed as a function of soil temperature. Within the observed temperature range (daily mean average 11–17°C), the Q10 (temperature coefficient) of in situ N mineralisation was 1.5. Negative values of N mineralisation were associated with the lower LC content of each period, indicating the presence of an immobilisation process, or that a proportion of LC was not involved in N mineralisation.
The effect of dry aggregation and percentage clay on sediment flux as measured by a portable field wind tunnel
Authors: Leys J , Koen T , McTainsh G
Published: April 2005

The effect of dry aggregation levels >0.85 mm and the percentage clay content of 9 soils from south-western New South Wales on erosion rate is evaluated using a portable field wind tunnel. Standard soil preparations and wind velocities are used based on conventions established in the North American wind erosion literature. For the prediction of erosion rate on both cultivated and uncultivated soils, 2 highly significant empirical relationships for percentage soil clay content and percentage mass dry aggregation >0.85 mm are presented. These spatial and temporal variations in erosion rates have significance for our understanding of soil erodibility. The concept of erodibility continuum is introduced.
Soil aggregate stability and soil organic matter fractions under agropastoral systems established in native savanna
Authors: Gijsman AJ
Published: April 2005

An area of native savanna on an Oxisol in the Eastern Plains of Colombia was opened and sown to various rotations of grass or grass-legume pasture with rice. After 4.5 years, the soil was sampled for studying the effect of land conversion on soil aggregation and on the distribution of total and particulate soil organic matter across the aggregate size classes. The size distribution of undisturbed aggregates did not vary among treatments. Five different methods were used to measure wet aggregate stability (WAS). The choice of method affected the WAS average across treatments as well as the differences among treatments. The only consistent observation was the lower WAS under monocropped rice compared with the other treatments. Inclusion of a legume in a pasture hardly affected aggregate stability. In contrast to the WAS measurements, which were carried out with soil aggregates of 1-2 mm, wet sieving of whole-soil samples revealed additional differences among treatments: large macroaggregates (>2 mm) proved less stable under those treatments that involved soil disturbance through ploughing and harvesting. Total soil C and N content did not vary among treatments, despite considerable differences in plant production levels. The C concentration, but not the N concentration, declined with decreasing aggregate size. The distribution of whole-soil C and N content across aggregate size classes depended more on the amount of soil in a certain size class than on the size class's C or N concentration. Those treatments that involved frequent soil disturbance had a smaller fraction of large macroaggregates (>2 mm) and, as a consequence, less C and N in the large macroaggregate fraction. The particulate organic matter (POM) fraction accounted for only 6.2-8.5% of total soil carbon. The small size of this pool makes it unlikely that POM can serve in these Oxisols for estimating the amount of soil organic matter with medium turnover rate, as suggested by others.