bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of the soil matrix on nitrogen mineralisation and nitrification. IV.Texture
Authors: Strong D. T. , Sale P. W. G. , Helyar K. R.
Published: January 2006

Small undisturbed soil volumes (c. 1·7
cm3) were collected from the surface of a small field
plot. Soil volumes were treated with clover-derived substrate, dried and
rewetted, or retained continuously moist from the field. These soil volumes
were then incubated for 20 days at a matric water potential of either
–10 or –30 kPa. At the end of the incubation the soil was analysed
for volumetric water content (θv),
NO-3 -N,
NH+4 -N, total N (%N), and
percentages of sand, silt, and clay. The texture terms were included in linear
regression models, together with %N and θv as predictors of N
mineralisation and nitrification.
Clay and sand were often observed to have a significant influence on N
mineralisation and nitrification, but silt rarely appeared to influence these
processes. In soils retained continuously moist, %clay had a negative
relationship with N mineralisation and nitrification, but this relationship
was positive in soils that had been dried and rewetted. The results suggest
that during periods of relatively high moisture content, soils that are higher
in clay are able to protect organic N more effectively from microbial attack.
However, on drying and rewetting, the protective mechanisms of clay are
undermined, the relatively large protected reservoirs of organic N in high
clay soils become more vulnerable to microbial attack, and these soils
therefore experience a greater flush of N mineralisation than soils with lower
clay levels. The negative influence of clay in the continuously moist soils
was not as clearly observed in the soils incubated at –10 kPa as in
soils incubated at –30 kPa, suggesting that the decomposition of organic
N resident in larger pores (10–30 µm neck diameter) may not be as
strongly regulated by clay as that resident in smaller pores. When soils were
treated with clover-derived substrate, clay had a positive relationship with N
mineralisation and nitrification rates. This may have been because clay
limited the diffusion of partially decomposed organics away from the
decomposing microbial population, thereby helping to facilitate more complete
decomposition of the organic material. Texture had very little influence on
the nitrification of urea-derived ammonium.
Comparison of peroxide-oxidisable sulfur and chromium- reducible sulfur methods for determination of reduced inorganic sulfur in soil
Authors: Sullivan L. A. , Bush R. T. , McConchie D. , Lancaster G. , Haskins P. G. , Clark M. W.
Published: January 2006

The rational management of acid sulfate soils requires analytical methods that
provide reliable and accurate data on the content of reduced inorganic sulfur;
it is this fraction that produces acid during oxidation. This study compared
the utility of the chromium-reducible sulfur method for determining the
reduced inorganic sulfur content of soil materials with methods based on
oxidation using hydrogen peroxide. The results presented here indicate that
methods involving oxidation by hydrogen peroxide for the determination of
reduced inorganic sulfur are subject to significant interference by even minor
amounts of sulfate minerals and organic matter, resulting in inaccurate
determinations of reduced inorganic sulfur contents. In the presence of even
minor amounts of gypsum, methods involving oxidation using hydrogen peroxide
underestimated reduced inorganic sulfur contents by up to 0·167%
sulfur, whereas in the presence of organic matter these methods overestimated
reduced inorganic sulfur contents by up to 0·077% sulfur per
cent organic carbon. The resulting errors in the determinations of reduced
inorganic sulfur by hydrogen peroxide methods were often larger than the
action criteria that are currently used to identify acid sulfate soils.
Consequently, there is a risk of misidentification of acid sulfate soils
(either false positive or false negative) for soils with low reduced inorganic
sulfur contents when hydrogen peroxide methods are used. In contrast, the
results from the chromium-reducible sulfur method do not appear to be affected
by interferences from either gypsum or organic matter and this method appears
to be more suitable for the determination of reduced inorganic sulfur in soils
than methods based on oxidation using hydrogen peroxide.
Effect of calcined magnesite on soil and Pinus radiata foliage magnesium in pumice soils of New Zealand
Authors: Mitchell A. D. , Loganathan P. , Payn T. W. , Tillman R. W.
Published: January 2006

Magnesium (Mg) deficiency is common in a number of forest regions in the
world. It has been linked to a condition in P. radiata
called ‘upper mid crown yellowing’ (UMCY) in New Zealand and
‘new type forest decline’ in Europe. Mg concentrations are low in
many of New Zealand"s forest soils. With increases in the number of
rotations and increased growth rates through tree breeding, Mg deficiency is
expected to increase.
This study was conducted to determine the fate of calcined magnesite (calmag)
fertiliser applied at 150 kg Mg/ha at 2 sites in the Kaingaroa Forest near
Rotorua, New Zealand. It also investigated the effectiveness of calmag in
increasing the soil solution and soil exchangeable Mg in pumice soils and Mg
concentrations in the pine needles, and in reducing the likelihood of UMCY 2
and 3 years after fertiliser application.
In both sites and for both years of sampling the application of calmag
fertiliser resulted in a significant increase in soil exchangeable and soil
solution Mg in the 0–5 cm soil layer. Soil and soil solution pH had also
been increased in the top 5 cm soil layer. Two years after application about
90% of the fertiliser applied had dissolved and about
70–80% of the Mg remained in a plant-available form (ammonium
acetate exchangeable Mg) in the top 10 cm of soil. Calculations suggest that
3–10% of applied fertiliser had been lost due to leaching.
Magnesium fertiliser application also resulted in significant reduction in the
exchangeable K: Mg ratio and reduced exchangeable Al in the 0–5 cm soil
layer. After 3 years, foliar Mg concentrations increased at all sites in the
fertilised trees compared with the control trees, although differences were
not yet significant. UMCY severity in the trees was also not significantly
affected by the application of Mg fertiliser.
Assessment of peroxide oxidation for acid sulfate soil analysis. 1. Reduced inorganic sulfur
Authors: Ward Nicholas J. , Sullivan Leigh A. , Bush Richard T. , Lin Chuxia
Published: January 2006

The reduced inorganic sulfur fraction of 4 acid sulfate soil (ASS) materials
was quantified using a variety of peroxide oxidation procedures. The
temperature and duration of the peroxide oxidation were found to markedly
affect the peroxide oxidisable sulfur determination. For 3 ASS materials with
low total carbon content (i.e. <2.5% C), peroxide oxidisable sulfur
underestimated the reduced inorganic sulfur fraction, with the peroxide
oxidisable sulfur determinations being as low as 42% of those
determined using chromium reducible sulfur technique. The precipitation of
jarosite during peroxide oxidation was a major factor contributing to the
underestimation of reduced inorganic sulfur in these materials. Apparent
losses of sulfur of approximately 25% on average occurred during
peroxide oxidation budget accounting; this also contributed towards the
observed underestimation of reduced inorganic sulfur. It is most likely that
these unaccounted losses are due to atmospheric losses of sulfur. In a peat
ASS, one of the peroxide oxidation methods overestimated the reduced inorganic
sulfur fraction and was attributed to the release of a large reserve of
organic sulfur in this material by the peroxide. This study shows the peroxide
oxidation methods examined here are subject to substantial interferences.
Consequently these peroxide oxidation methods are unable to reliably provide
accurate measurements of the reduced inorganic sulfur fraction in ASS
materials.
pyritic sulfur, peroxide oxidisable sulfur, chromium reducible sulfur,
jarosite, sulfur budget.
Assessment of peroxide oxidation for acid sulfate soil analysis. 2. Acidity determination
Authors: Ward Nicholas J. , Sullivan Leigh A. , Bush Richard T. , Lin Chuxia
Published: January 2006

Total sulfidic acidity (TSA) and total potential acidity (TPA) are derived
from peroxide oxidation of acid sulfate soil materials (ASS), and are measures
of the sulfidic acidity and the net acidity (net acidity = sulfidic
acidity + actual acidity – acid neutralising capacity),
respectively. The TSA and TPA of 4 ASS materials were determined using a
variety of peroxide oxidation procedures and compared with the sulfidic
acidity and net acidity derived from the use of an acid–base accounting
model. TSA and TPA values both varied greatly with each peroxide oxidation
method used, and both measures were found to substantially underestimate (i.e.
by 23–85%) both sulfidic acidity (as determined from the chromium
reducible sulfur content) and net acidity (as determined by acid–base
accounting). A major cause of this underestimation of acidity was the
retention of acidity through the precipitation of jarosite during peroxide
oxidation. Substantial clay mineral dissolution appears to have occurred
during peroxide oxidation of the ASS materials, as indicated by increased
soluble aluminium. Such dissolution may contribute to the underestimation of
both sulfidic and net acidity for the ASS materials using peroxide oxidation
methods. The loss of acidity to the atmosphere was identified as a possible
additional interference. This study shows the peroxide oxidation methods
examined here are subject to substantial interferences, which caused large
underestimations of acidity, and consequently, are unable to reliably provide
accurate measurements of sulfidic and net acidity in ASS materials.
pyritic sulfur, total potential acidity, total sulfidic acidity, net
acidity, jarosite, acid budget, acid neutralising capacity.
Effect of cattle treading on interrill erosion from hill pasture: modelling concepts and analysis of rainfall simulator data
Authors: Elliott A. H. , Tian Y. Q. , Rutherford J. C. , Carlson W. T.
Published: January 2006

Damage to pasture as a result of intensive grazing and treading by cattle increases the erosion of sediment and associated nutrients. In this study we present a model for the effect of treading damage on interrill erosion. The model formulation is based on the interrill erosion components of conventional process-based erosion models, with some modifications. The model was developed using data from small rainfall simulator plots (0.5 m2) on hill-country pasture in New Zealand with varying amounts of treading damage. Treading increased the amount of bare ground, and this resulted in increased concentrations of sediment in runoff. Concentration was found to increase linearly with the amount of bare ground. Treading resulted in increased runoff, which had some effect on sediment concentration for the high runoff rates in the experiments, but would have a negligible effect on concentration for typical natural runoff rates. However, the increased runoff results in greater sediment loads because a larger volume of sediment-laden runoff is produced. The increase in runoff was modelled through a reduction factor for the hydraulic conductivity which varied linearly with the fraction of damaged ground. For 100% damaged ground the hydraulic conductivity was approximately halved. The recovery of bare ground and damaged ground over time after treading was also assessed. Bare ground resulting from treading typically halved after 2 months, while damage took longer to recover. Such treading-related effects are superimposed on seasonal variations in erodibility, bare ground, and infiltration capacity. Based on the results of the study, some measures to reduce treading-related erosion are suggested.
Soil nitrogen availability predictor (SNAP): a simple model for predicting mineralisation of nitrogen in forest soils
Authors: Paul K. I. , Polglase P. J. , O'Connell A. M. , Carlyle J. C. , Smethurst P. J. , Khanna P. K.
Published: January 2006

A new empirical model (SNAP) combines a simple laboratory measurement of the basal rate of N mineralisation with the modifying effects of daily temperature and water content to predict seasonal and annual rates of mineralisation of forest soils. Short-term (20-60-day) aerobic incubations of either undisturbed or bulked and mixed soil were found suitable for prediction of the basal rate of N mineralisation. Data from laboratory incubations of a range of soils were used to calibrate empirical relationships describing the effects of temperature (Tm) and water (Wm) on rates of N mineralisation. Submodels for predicting daily average temperature (STUF) and water content (SWUF) for up to 3 surface soil layers were developed and used to provide inputs to the Tm and Wm functions, respectively. Inputs required for SNAP are restricted to variables whose values are easily obtained. In addition to the amount of N mineralised during a short aerobic laboratory incubation, other soil properties required are bulk density, gravel and clay content, and upper and lower limits of soil water content. Climatic data required included daily air temperature, rainfall, and solar radiation. Other inputs are slope, leaf area index of the stand, and approximate mass and height of litter. Predicted rates of N mineralisation have been verified using data from 9 native forests, 12 radiata pine plantations, and 12 eucalypt plantations from across southern Australia. Despite the wide range of forest types, soil types, climatic regions, and management systems, predicted annual rates of N mineralisation were in close agreement with those observed in the field, regardless of whether daily soil temperature and water content were predicted (R2 = 0.76, P < 0.001, n�=�127) or observed (R2 = 0.78, P < 0.001, n = 68). Sensitivity analysis showed that it was most important to minimise analytical error in inputs used to calculate the basal rate of N mineralisation (i.e. soil temperature, water content, and N mineralised during laboratory incubation). The model was more sensitive to daily soil temperature than to daily soil water content.
Soil erosion rates under intensive vegetable production on clay loam, strongly structured soils at Pukekohe, New Zealand
Authors: Basher L. R. , Ross C. W.
Published: January 2006

Rates of soil redistribution by water and tillage erosion were determined in 3 fields under long-term continuous vegetable production on clay loam, strongly structured soils derived from volcanic ash at Pukekohe, South Auckland, New Zealand. Erosion and deposition rates were estimated using a mass balance model to convert variation in 137Cs areal activity within the fields to estimates of erosion and deposition.

Caesium-137 areal activity in cropped fields ranged from 171 to 2144 Bq/m2, compared with a reference value under permanent pasture of 774 Bq/m2. There was a characteristic pattern of 137Cs distribution within each field, with differences between the fields related to variation in topography. Lowest values of 137Cs were found in the upper parts of each field and highest values towards the base of each field. In all 3 fields there was a net loss of 137Cs, ranging from 13 to 32%, with an average over the 3 fields of 18%. Net rates of soil loss from the fields were 30, 11, and 7 t/ha.year. However, within the fields there was a much wider range of both erosion (up to 92 t/ha.year) and deposition (up to 100 t/ha.year) rates. Most of the soil redistribution is caused by water erosion, with tillage erosion accounting for 10-20% of the soil redistribution. The soil redistribution rates were 2 orders of magnitude higher than sediment export measured at small catchment scale. Soil erosion rates are not reflected in variation in topsoil depth, because frequent tillage and incorporation of organic residues maintains a uniform topsoil depth, but soil deposition rates are closely related to topsoil depth.
Spatial and seasonal distribution of rainfall erosivity in Australia
Authors: Lu Hua , Yu Bofu
Published: January 2006

Spatially distributed rainfall erosivity and its seasonal distribution are needed to use the revised universal soil loss equation (RUSLE) for erosion risk assessment at large scale. An erosivity model and 20-year daily rainfall data at 0.05° resolution were used to predict the R-factor and its monthly distribution for RUSLE in Australia. Predicted R-factor values were compared with those previously calculated using pluviograph data for 132 sites around Australia. The daily erosivity model was further evaluated for 43 sites where long-term pluviograph data were available. Predicted and calculated monthly distributions of the R-factor were compared for these 43 sites. For the 132 sites where R-factor values were compiled from previous investigations, the model efficiency was 0.81 with root mean squared error (rmse) of 1832 MJ.mm/(ha.h.year), or 47.5% of the mean for the 132 sites. For the additional 43 sites, the coefficient of efficiency was 0.93 with a 12.7 mm rainfall threshold, and 0.94 when all storms were included in the calculations. The rmse was 908 MJ.mm/(ha.h.year), or 28.6% of the mean for the 43 sites with a zero rainfall threshold. The prediction error for monthly distribution of the R-factor was 2.3% with a zero threshold and 2.5% with 12.7�mm threshold. This and previous studies have shown that the daily rainfall erosivity model can be used to accurately predict the R-factor and its seasonal distribution in Australia. Digital maps were produced showing the spatial and seasonal distribution of the R-factor at 0.05° resolution in Australia. These maps have been used to assess rill and sheet erosion rate at the continental scale.
Nitrate retention under sugarcane in wet tropical Queensland deep soil profiles
Authors: Rasiah V. , Armour J. D. , Menzies N. W. , Heiner D. H. , Donn M. J. , Mahendrarajah S.
Published: January 2006

Nitrate leaching below the crop root-zone in variable charge soils may be adsorbed at anion exchange sites, thereby temporarily reducing the risk of contamination of water bodies. The objectives of this study were (i) to investigate whether nitrate adsorption, accumulation, and retention in the Johnstone River Catchment of Far North Queensland wet tropics is widespread; (ii) to assess the capacity of soil in the Johnstone River Catchment to retain nitrate; and (iii) to deduce the consequences of nitrate adsorption/desorption on contamination of water bodies. Soil cores ranging from 8 to 12.5 m depth were taken from 28 sites across the catchment, representing 9 Ferrosol soil types under sugarcane (Saccharum officinarum-S) cultivation for at least 50 years and from rainforest. The cores were segmented at 0.5-m depth increments and subsamples were analysed for nitrate-N, cation and anion exchange capacities, pH, exchangeable cations (Ca, Mg, K, Na), soil organic C, electrical conductivity, sulfate-S, and chloride. Nitrate-N concentration under sugarcane ranged from 0 to 72.5 mg/kg, compared with 0 to 0.31 mg/kg under rainforest, both Pin Gin soils. The average N load in 1–12 m depth across 19 highly oxidic profiles of the Pin Gin soil series was 1550 kg/ha, compared with 185 kg/ha under 8 non-Pin Gin soils and 11 kg/ha in rainforest on a Pin Gin soil. Most of the nitrate retention was observed at depth of 2–12 m, particularly at 4–10 m, indicating that the accumulation was well below the crop root-zone. The average maximum potential nitrate retention capacity was 10.8 t/ha for the Pin Gin and 4.7 t/ha for the non-Pin Gin soil. Compared with the current N load, the soils still possess a large capacity to adsorb and retain nitrate in profiles. Retention of large quantities of the leached nitrate deep in most of the profiles has reduced the risk of contamination of water bodies. However, computations show that substantial quantities of the nitrate leached below the root-zone were not adsorbed and remain unaccounted for. This unaccounted nitrate might have entered both on- and off-site water bodies and/or have been denitrified.
Simultaneous estimation of several soil properties by ultra-violet, visible, and near-infrared reflectance spectroscopy
Authors: Islam Kamrunnahar , Singh Balwant , McBratney Alex
Published: January 2006

Fast and convenient soil analytical techniques are needed for soil quality assessment and precision soil management. Spectroscopy in the ultraviolet (UV, 250–400 nm), visible (VIS, 400–700 nm), and near-infrared (NIR, 700–2500 nm) ranges allows rapid acquisition of soil information at quantitative, and qualitative or indicator, levels for use in agriculture and environmental monitoring. The main objective of this study was to evaluate the ability of reflectance spectroscopy in the UV, VIS, and NIR ranges to predict several soil properties simultaneously. Soil samples (161 surface and subsurface) were used for simultaneous estimation of pH, electrical conductivity (EC), air-dry gravimetric water content, organic carbon (OC), free iron, clay, sand, and silt contents, cation exchange capacity (CEC), and exchangeable calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na). Principal component regression analyses (PCA) were used to develop calibration equations between the reflectance spectral data and measured values for the above soil properties obtained by traditional laboratory methods. By using randomly selected calibration and validation sets of samples, PCA models were able to successfully predict pH, OC, air-dry gravimetric water content, clay, CEC, exchangeable Ca, and exchangeable Mg of soil samples. The predictions, however, were poor for EC, free iron, sand, silt, exchangeable K, and exchangeable Na. The study shows that reflectance spectroscopy in the UV–VIS–NIR range has the potential for the rapid simultaneous prediction of several soil properties.
Effect of soil amendment with bauxite Bayer process residue (red mud) on the availability of phosphorus in very sandy soils
Authors: Snars Katherine , Gilkes Robert , Hughes Jeffrey
Published: January 2006

The chemical properties of red mud, a by-product of Bayer process refining of bauxite to alumina, make disposal of the material problematic. It is very alkaline (pH >11), contains a large amount of sesquioxides, and thus has a very high P retention capacity. These characteristics have encouraged its use as a soil amendment to enhance P retention of soils so as to reduce leaching of P. To investigate the effect of added red mud on the availability of existing P in sandy soils an incubation experiment was conducted using 3 types of red mud (untreated red mud, red mud amended with 5% gypsum, and red mud leached with dilute acid to remove all soluble salts) mixed with 12 podsol topsoils at rates of 0, 2.5, 5, 10, 20, and 40�t/ha. The mixtures were incubated wet for 28 days in the dark at 20°C, both with and without a microbial inhibitor. The decrease in 0.5 M sodium bicarbonate extractable phosphorus (bic-P) was 40–60% of initial bic-P at 40 t/ha of all 3 red muds after wet incubation without microbial suppressant. This decreased to 20–40% after drying or with addition of the microbial suppressant. The decrease in bic-P was not due to the increase in pH due to red mud application and appears to involve both chemical and microbial actions. The increase in soil pH of up to 3 units would be beneficial for pasture production at most rates of red mud application and the associated increase in electrical conductivity is not sufficient to affect plant growth.
Ammonium oxidation kinetics in the presence of nitrification inhibitors DCD and DMPP at various temperatures
Authors: Irigoyen Ignacio , Muro Julio , Azpilikueta Miren , Aparicio-Tejo Pedro , Lamsfus and Carmen
Published: January 2006

Use of N-based fertilisers in combination with nitrification inhibitors lengthens N presence in the ammonium form in soil (N-NH4+), with beneficial effects for agriculture and related ecosystems. The efficiency of these inhibitors depends on several factors, the most important being soil temperature. This paper studies the effects of soil temperature on the kinetics of N-NH4+ loss in the presence of the DCD and DMPP nitrification inhibitors. For a 105-day period, 3 chambers, each with 12 containers holding 500 g of dry soil, were incubated at 10, 20, and 30�C. Ammonium sulfate was applied to 4 containers in each chamber; in another 4 containers Basammon Stabil, a N fertiliser with DCD, was used; and Entec 26, a fertiliser with DMPP, was used in the remaining 4 containers. Soil ammonium content was periodically determined for each container. Both DCD and DMPP lengthened ammonium presence in soil in a similar manner. However, their effectiveness was drastically decreased at increased soil temperatures. Thus, when using these inhibitors, soil temperature should be taken into account, especially in warm climate areas.
Microbial and chemical tracer movement through two Southland soils, New Zealand
Authors: McLeod M. , Aislabie J. , Ryburn J. , McGill A. , Taylor M.
Published: January 2006

There has been a recent, rapid increase in both land application of dairy shed effluent in Southland, New Zealand, and the microbial load in ground and surface waters. We investigated the fate of faecal coliforms, a host-specific Salmonella bacteriophage, and a non-reactive chemical tracer (Br–), when applied to large intact lysimeter soil cores (500 mm diam. by 500 mm high), to determine the pattern of microbial transport through typical Southland soils. The soils were a poorly drained Fragic Perch-gley Pallic Soil, and a well-drained Typic Firm Brown Soil. A depth of 25 mm of dairy shed effluent containing faecal coliforms and spiked with bacteriophage and Br– was applied to the soil at a rate of 5 mm/h followed by ~1 pore volume of simulated rainfall applied at 5 mm/h. Resulting leachates, collected continuously over ~1 pore volume, were analysed for the microbial and bromide tracers. The microbial tracers moved rapidly through both soils, peaking early in the leachate at ~0.15 pore volume and then tailing off in a pattern indicative of bypass flow. Bromide moved more uniformly through the soils but peaked at ~0.5–0.8 pore volume. The microbial flow pattern observed indicates that the structure in these soils makes them vulnerable to leaching of microbes into local surface and ground water. The large difference between the rate of microbial and chemical tracer transport indicates chemical tracers should only be used with caution to model microbial transport parameters.
Soil testing for phosphorus: comparing the Mehlich 3 and Colwell procedures for soils of south-western Australia
Authors: Bolland M. D. A. , Allen D. G. , Walton K. S.
Published: January 2006

Soil samples were collected from 14 long-term field experiments in south-western Australia to which several amounts of superphosphate or phosphate rock had been applied in a previous year. The samples were analysed for phosphorus (P) by the Colwell sodium bicarbonate procedure, presently used in Western Australia, and the Mehlich 3 procedure, being assessed as a new multi-element test for the region. For the Mehlich procedure, the concentration of total and inorganic P in the extract solution was measured. The soil test values were related to yields of crops and pasture measured later on in the year in which the soil samples were collected.The Mehlich 3 procedures (Mehlich 3 total and Mehlich 3 inorganic soil test P values) were similar, with the total values mostly being slightly larger. For soil treated with superphosphate, for each year of each experiment: (i) Mehlich 3 values were closely correlated with Colwell values; and (ii) the relationship between plant yield and soil test P (the soil P test calibration) was similar for the Colwell and Mehlich 3 procedures. However, for soil treated with phosphate rock, the Colwell procedure consistently produced lower soil test P values than the Mehlich 3 procedure, and the calibration relating plant yield to soil test P was different for the Colwell and Mehlich 3 procedures, indicating, for soils treated with phosphate rock, separate calibrations are required for the 2 procedures. We conclude that for soils of south-western Australia treated with superphosphate (most of the soils), the Mehlich 3 procedure can be used instead of the Colwell procedure to measure soil test P, providing support for the Mehlich 3 procedure to be developed as the multi-element soil test for the region.
Predicting sheetwash and rill erosion over the Australian continent
Authors: Lu Hua , Prosser Ian P. , Moran Chris J. , Gallant John C. , Priestley Graeme , Stevenson Janelle G.
Published: January 2006

Soil erosion is a major environmental issue in Australia. It reduces land productivity and has off-site effects of decreased water quality. Broad-scale spatially distributed soil erosion estimation is essential for prioritising erosion control programs and as a component of broader assessments of natural resource condition. This paper describes spatial modelling methods and results that predict sheetwash and rill erosion over the Australian continent using the revised universal soil loss equation (RUSLE) and spatial data layers for each of the contributing environmental factors. The RUSLE has been used before in this way but here we advance the quality of estimation. We use time series of remote sensing imagery and daily rainfall to incorporate the effects of seasonally varying cover and rainfall intensity, and use new digital maps of soil and terrain properties. The results are compared with a compilation of Australian erosion plot data, revealing an acceptable consistency between predictions and observations. The modelling results show that: (1) the northern part of Australia has greater erosion potential than the south; (2) erosion potential differs significantly between summer and winter; (3) the average erosion rate is 4.1 t/ha.year over the continent and about 2.9 × 109 tonnes of soil is moved annually which represents 3.9% of global soil erosion from 5% of world land area; and (4) the erosion rate has increased from 4 to 33 times on average for agricultural lands compared with most natural vegetated lands.
Influence of changed management of sugarcane on some soil chemical properties in the humid wet tropics of north Queensland
Authors: Noble A. D. , Moody P. , Berthelsen S.
Published: January 2006

A study was undertaken to quantify changes in chemical attributes and cation exchange characteristics of soils associated with two forms of changed management in sugar production systems 6–9 years after their implementation. The two production systems included a long-term green cane trash blanketed (GCTB)/burn trial and a rotation experiment established to investigate crop management strategies to reduce the effects of yield decline in long-term sugarcane monocultures. The treatments investigated in the latter trial were (a) long-term continuous GCTB, (b) grass ley, and (c) a bare fallow treatment. Under both the GCTB and grass ley systems, pH significantly declined over 6 years with an associated increase in aluminium saturation and decline in base saturation of the cation exchange complex. Although the decline in base saturation under the GCTB treatment would effectively indicate a degree of degradation, this base diminution is easily reversed through conventional management strategies. Organic carbon levels increased by 4 t/ha under the GCTB treatments compared with the burnt over a 9-year period. In contrast, under a grass ley system, organic carbon increased by 9 t/ha over a 6-year period compared with continuous cane, clearly demonstrating the superior nature of grass leys in sequestering carbon in this tropical environment. The increased net proton addition in the GCTB system relative to the burnt system was estimated to be 0.71�kmol H+/ha.year, and the net proton additions for the continuous cane, grass ley, and fallow systems were 1.38, 3.81, and 0.87 kmol H+/ha.year, respectively. The cation exchange characteristics were derived from bulk samples collected from each of the trials. The divergence between the cation exchange curves due to treatment was greatest in the surface 10 cm, but this diminished with depth, indicating that the influence of trash retention or grass leys on soil charge characteristics was confined to the surface layer. The increases in cation exchange capacity (CEC) at pH 5.5 of the GCTB treatment compared with the burnt, and of the grass ley treatment compared with the continuous cane, were estimated to be 0.67 and 0.75 cmolc/kg over the 0–10 cm depth interval. Plots of effective CEC v. CEC clearly indicated that 9–31% of the cations measured where not associated with the exchange complex and would therefore be subject to leaching loss. Organic C oxidisable by 33 mM KMnO4 (C1) or 333 mM KMnO4 (C3) was highly linearly correlated with total organic C across both sites and all treatments. This suggests that the proportions of different functional organic groups were not greatly affected by burning, trash retention, or pasture.
Particle density and the plummet balance
Authors: Emerson W. W. , Weissmann D.
Published: January 2006

Soil suspensions are usually characterised by the percentage weights of
particles settling with velocities between defined limits, such as silt and
clay. If percentages were measured sufficiently accurately by both the pipette
method and a plummet balance, dry densities of fractions could be calculated
and hence their composition inferred. The accuracy and precision of the
pipette method were confirmed by the mass balance of particles in peptised
suspensions of a red-brown earth subsoil and a kaolinite. Percentages
indicated by a plummet balance were corrected for the actual densities of
fractions measured separately. Residual differences from the pipette values
showed that the balance was accurate but lacked the precision needed to deduce
densities to 0.01 mg/mm3.
Values of the density of clay fractions were deduced from the means of
published percentages obtained by the two methods where replicate suspensions
were used and also from the mean difference based on a comparison using 199
soil samples. For the latter, an underestimate of clay percentages indicated
by the balance had first to be allowed for. Clay-deduced densities were in the
range 2.80–2.83 mg/mm3, compared with 2.84
mg/mm3 measured on the separated subsoil clay. The
values are similar, probably because the clays are derived from mica. The
density of the separated subsoil silt was 2.64
mg/mm3, less than quartz, because of the presence of
feldspar. Such results indicate the potential use of the method if the
precision of the balance is improved.
Categories of soil structure based on mechanical behaviour and their evaluation using additions of lime and gypsum on a sodic Vertisol
Authors: Chan K. Y. , Chan K. Y. , Dexter A. R. , Dexter A. R. , McKenzie D. C. , McKenzie D. C.
Published: January 2006

Measurements of soil aggregate strength were made using a simple crushing
(indirect tension) test. The resulting values of strength were used to examine
aspects of the internal structure of the soil aggregates. This was done using
2 methods: firstly, by studying the dependence of aggregate tensile strength
on aggregate size; and secondly, by studying the variability of strength
measurements made on aggregates of one size. Combination of the results from
the 2 methods enables some new categories of soil behaviour to be defined.
The new categories were evaluated using soil samples collected from a field
experiment in which additions of lime and gypsum were made to a sodic
Vertisol. The use of the new categories leads to the conclusion that the added
compounds resulted in larger aggregates being weaker than the smaller
aggregates. This was partly due to a greater amount of micro-cracking in the
larger aggregates, and partly due to a greater weakening of the matrix within
the larger aggregates. Both of these changes are consistent with the soil
being more friable after the additions of the calcareous amendments. It was
not possible to distinguish qualitatively between the effects of lime and
gypsum. It is suggested that the amendments did not modify the soil structure
directly, but that they increased the tendency of the soil to self-mulch in
response to wetting and drying cycles.
Sediment generation from forest roads: bed and eroded sediment size distributions, and runoff management strategies
Authors: Connolly R. D. , Costantini A. , Loch R. J. , Garthe R.
Published: January 2006

A rainfall simulator and overland flow study was conducted to determine
in situ and eroded sediment size distributions for a
range of forest road surfaces at 2 important commercial plantation centres in
subtropical south-east Queensland, Australia; and parameters necessary for
running the CREAMS model to assess erosion and sediment transport from
road/table drain systems.
Results revealed very low concentrations of fine particles in the surface of
gravel roads, and somewhat higher proportions in ungravelled (dirt) road
surfaces. However, there was considerable enrichment of fine particles in
sediment eroded under simulated rain, with concentrations of particles <0
. 02 mm in diameter being up to 8 g/L.
Table drains were generally resistant to scour by overland flows, with the
only exception being a drain bordering a newly gravelled road. This drain was
bare of vegetation and contained significant quantities of loose gravel from
which the fine component was easily eroded. It demonstrated the need to
construct both roads and table drains at the end of the wet season when
consolidation and re-vegetation can occur under lighter rains during the dry
season.
CREAMS model runs for a ‘standard’ road and drain configuration
predicted considerable enrichment of fine particles in sediment from all road
surfaces. The major factor controlling predicted concentrations of fine
particles was the rate of erosion from the road surface, with gravelled
surfaces showing considerably less erosion than ungravelled surfaces.
Because road surfaces will be significant sources of fine sediment during
erosive rains, a second part of this study was designed to model whether
hillslopes could be used to infiltrate runoff, thereby controlling sediment
movement. For the modelled hillslopes—typical of those used to support
commercial forest plantations in south-east Queensland—design runoffs
from forest road turn-out drains could be infiltrated. It is suggested that
forest managers use hillslope infiltration as the primary tool for managing
flows and sediments from road turn-out drains, and that vegetative filter
strips be used only as a secondary support tool.
Aluminium speciation in seasonally dry high country soils, South Island, New Zealand
Authors: Adams M. L. , McIntosh P. D. , Patterson R. D. , Powell K. J.
Published: January 2006

Soil solutions from an altitude sequence of South Canterbury high country
soils (730– 1190 m) were analysed using a recently developed technique
to obtain values for ‘free Al’ ([Al
3+ ]+[Al(OH)
2+ ]+[Al(OH)2
+ ]+[AlF
2+ ]), an ‘organic-bound Al’
fraction, and the Al- complexation capacity (Al-CC). From 1979 these soils
have been fertilised, oversown, and grazed. Since 1978, topsoils (0–7
. 5 cm) have become more acid, and average
pH(H 2 O) (1 : 2 . 5 soil :
H2O; n = 38) has fallen
from 5 . 79 in 1978 to 5 . 25 in 1996. Despite this soil
acidification, the current ‘free Al’ values are low (0 .
31–0 . 75 µМ) and are unlikely to
limit legume growth. This conclusion was supported by root elongation
experiments using Medicago sativa (Wairau lucerne). No
significant correlation was observed between measured root elongation and
either soil solution pH or ‘free Al’.
Sunny aspects had higher ‘organic-bound Al’ and lower ‘free
Al’ values. The values of p[Al 3+ ]
calculated from ‘free Al’ were consistent with control of [Al
3+ ] by an Al(OH)3(s)
phase rather than by organic matter. ‘Organic-bound Al’ correlated
strongly with the concentration of humic substances in soil solution as
estimated by the UV absorbance at 250 nm. The Al-CC decreased with a decrease
in soil solution pH. Relative to the total reactive Al, the capacity of soil
solutions to complex Al, as may be generated by acidification, was lower for
the soils at lower elevations, pointing to potential for an earlier onset of
Al toxicity at these sites.
A comparison of three soil tests for assessing Cd accumulation in wheat grain
Authors: Oliver D. P. , Tiller (dec.) K. G. , Alston A. M. , Cozens G. D. , Naidu R.
Published: January 2006

Three extractants, namely ethylenediamine tetraacetic acid (EDTA),
CaCl2, and
Ca(NO3)2, were compared to assess
the relationship between the amounts of cadmium (Cd) extracted from soil and
the Cd concentration of wheat grain, with the view to using a soil test for
predicting Cd concentrations in grain. The soils used came from 1 glasshouse
experiment and 31 field sites sampled over 2 years, and they had received Cd
only from historical applications of phosphatic fertilisers. The soils ranged
from a heavy clay with a comparatively high carbon content to a sandy soil.
The pH values ranged from 4.5 to 7.8. The relationship between Cd
concentration in grain and CaCl2- and
Ca(NO3)2-extractable soil Cd was
variable and for most cases r2
value was <0.6. The use of pH alone to predict Cd concentration in wheat
grain was significant (P < 0.05) for all soils used
in the glasshouse except the soil with the highest clay content (Inman
Valley). In the field experiments, the relationships between Cd concentration
in grain and soil pH were significant (P < 0.05) but
the r2 values were low, ranging
from 0.28 to 0.66.
The inclusion of pH and extractable soil Cd (CaCl2- and
Ca(NO3)2-extractable) to determine
Cd concentration in grain only improved the relationship in one half of the
cases in this study. This suggests that there may be little to be gained in
prediction of Cd concentration in grain from the use of extractants compared
with using soil pH. Soil pH is also an easier, cheaper, and quicker
measurement than an extractable soil Cd measurement, particularly in soils
with low Cd concentrations where the extraction procedure involves a
concentration step. In all cases, grain Cd concentration and EDTA-extractable
soil Cd were poorly correlated.
Degradation of soil structure due to coalescence of aggregates in no-till, no-traffic beds in irrigated crops
Authors: Cockroft B. , Olsson K. A.
Published: January 2006

Poor soil structure remains a major restriction to achieving potential yields
from crops under zero tillage. Even water-stable, untrafficked soils in which
plants experience no limitations due to nutrients, water, or drainage almost
inevitably harden within 2–3 months after the initial cultivation. Most
agricultural scientists have not recognised the importance of this common yet
distinct form of soil hardening, which we name coalescence.
We identify coalescence as a slow increase in soil hardness which develops
during cycles of wetting and drying. The structure of a well-prepared bed of
soil that is water-stable and not trafficked changes to one that is hard,
although perforated with biopores. These pores facilitate the infiltration of
water, drainage, and some growth of roots, but the hard matrix causes root
growth and activity to be substantially reduced compared with roots in loose
soil and this reduces the productivity of the crop. We suggest that
coalescence is an important cause of poor responses in productivity to zero
and minimum tillage systems of soil management.
We have found isolated examples of soils in the field that remain soft, loose,
and porous, after more than 2 years since cultivation. This suggests that it
might be possible to prevent coalescence. These coalescence-stable soils, in
common with virgin soils, have properties that enable them to resist
coalescing. Although we do not know what these properties are, high organic
matter (>4% w/w total C content) is closely related to zero
coalescence. We do not understand why we observe low coalescence in some field
situations and we have been unable to control coalescence in the field.
Denitrification and immobilisation in flood-irrigated alkaline grey clays as affected by nitrification inhibitors, wheat straw, and soil texture
Authors: Rochester I. J. , Constable G. A.
Published: January 2006

Published field studies have shown that etridiazole and other nitrification
inhibitors may significantly improve N fertiliser recovery in alkaline grey
clays. Laboratory experiments were conducted to examine the extent to which
nitrification inhibitors could suppress denitrification directly in
waterlogged soil, and determine whether this may contribute significantly to
the conservation of N fertiliser in the field. Etridiazole reduced the loss of
added nitrate-N from waterlogged soil in the short term (days) only. All other
nitrification inhibitors failed to suppress N loss. Little nitrate-N was lost
from soil maintained at field capacity, whereas 15–85% of applied
nitrate was lost from soil that was waterlogged for 10 days. The addition of
milled wheat straw encouraged both denitrification and biological N
immobilisation to similar extents, although both processes were probably
restricted by C availability. Where no straw was added, little N was
immobilised and denitrification was halved. Soil texture (clay content) also
had a profound influence on N fertiliser recovery (N loss). The laboratory
experiments indicated that a component of the responses to etridiazole
observed in published field experiments conducted on these soils could be
attributed to direct suppression of denitrification by etridiazole.
Root-zone hydraulic lift evaluated with the dual-probe heat-pulse technique
Authors: Song Y. , Kirkham M. B. , Ham J. M. , Kluitenberg G. J.
Published: January 2006

Roots are movers of water in the soil. One method of movement is through
hydraulic lift, which occurs when plants extract water from a moist subsoil
and release it into a dry topsoil. Detection of hydraulic lift has been
hampered by the lack of instruments sensitive enough to measure the small
amount of water moved. Recently, the dual-probe heat-pulse (DPHP) technique
has been used to monitor with fine spatial resolution the soil water content
in root-zones. The objective of this research was to determine if water is
released by hydraulic lift, using the DPHP technique. Sunflower
(Helianthus annuus L.) was grown in a column (38 cm
height; 25 cm diam.; bulk density = 1.45
Mg/m3) packed with a Haynie very fine sandy loam
(coarse-silty, mixed, calcareous, mesic Mollic Udifluvents; FAO-Eutric
Fluvisols) with its roots divided between a top dry layer and a lower wet
layer. Eight DPHP sensors installed in the soil column were used to monitor
soil water content. During 24 measurement days, hydraulic lift was evident
only when the plant was wilted. This occurred when the lower ‘wet’
layer had been allowed to dry and then it was re-watered. At this time, the
roots in the upper dry layer released water, increasing the soil water content
in the centre of the root mass by 0.019
m3/m3 (increase from 0.121
m3/m3 to 0.140
m3/m3). The soil-water
increase was similar to other values reported in the literature and show it to
be small.