bluuebunny/crossref_metadata_2025 huggingface dataset:
Total C and N storage and organic C pools of a Red-Yellow Podzolic under conventional and no tillage at the Atlantic Forest Zone, south-eastern Brazil
Authors: Leite L. F. C. , Mendonça E. S. , Machado P. L. O. A. , Matos E. S.
Published: August 2003

A 15-year experiment in a clayey Red-Yellow Podzolic in the tropical highlands of Viçosa, Brazil, was studied in 2000, aiming to evaluate the impact of different management systems (no tillage, disk plowing, heavy scratcher + disk plowing, and heavy scratched) on the total organic carbon (TOC), total nitrogen (TN), and several organic carbon pools. A natural forest, adjacent to the experimental area, was used as reference. The greatest TOC and TN as well as microbial biomass C (CMB), light fraction C (CFL), and labile organic carbon (CL) stocks were observed in the Atlantic Forest, compared with all other systems. The long-term cultivation (±70 years) of this area, prior to the installation of the experiment, has led to soil degradation, slowing the C recovery. No tillage had the higher C and N stocks and greater CL pool at the surface (0–10 cm), indicating improvement in soil nutrient status, although none of the systems presented potential to sequester C-CO2. Sustainable tropical agricultural systems should involve high residue input and conservative soil management in order to act as a C-CO2 sink. The C stocks in the CMB, CFL, and CL compartments were more reduced in relation to the natural vegetation with higher intensity management than the TOC stocks. This result indicates that these C compartments are more sensitive to changes in the soil management.
Relationships between extractable Ni, Co, and other metals and some microbiological characteristics of different ultramafic soils from New Caledonia
Authors: Amir Hamid , Pineau René
Published: August 2003

New Caledonian ultramafic soils have relatively high metal content, which normally induces toxicity in plants and microflora. The relationships between extractable metal concentrations, especially Ni and Co, and different microbiological factors were analysed by statistical methods. For this purpose, some physico-chemical and microbiological characteristics of 40 ultramafic soil samples were estimated: organic carbon, pH, extractable metals (Ni, Co, Fe, Mn and Mg), microbial density, total microbial activity and percentage of microorganisms tolerant to Ni. Total, partial, and multiple correlation analyses are reported. The release of metals (measured by their extractablity) into these soils appeared to be related to microbial activity; the link with pH was not clear. A laboratory experiment confirmed the role of the microflora in the release of Ni and Co, which were not previously known to be released by microbial processes in soil. The percentage of microorganisms tolerant to Ni was highly correlated to the extractable concentration of this metal in the soils.
Effects of lanthanum on dehydrogenase activity and carbon dioxide evolution in a Haplic Acrisol
Authors: Chu H. Y. , Zhu J. G. , Xie Z. B. , Zhang H. Y. , Cao Z. H. , Li Z. G.
Published: August 2003

Rare earth elements (REEs) are applied widely to increase crop production in China but less attention has been paid to the principle adverse effects of the accumulation of REEs in soils. In this paper we studied the effects of lanthanum (La) on two indicators of microbial activity: dehydrogenase activity and CO2 evolution. The soil was collected from crop land of the Chinese Academy of Sciences' Red Soil Ecological Experimental Station. Application of La decreased soil pH and there were significant negative correlations between soil pH and added La. Significant positive correlations were also observed between 0.05 M HCl extractable La and added La, indicating that exogenous La was highly available in soil. Additions of La decreased soil dehydrogenase activity and the recorded maximum decrease was 64% after 1 day of incubation with an application of 1000 mg La/kg dry soil. The inhibition of soil dehydrogenase activity by La was gradually alleviated on prolonged incubation time. Addition of La at low concentrations slightly increased soil CO2 evolution but decreased it if at greater concentrations. The recorded maximum decrease in soil CO2 evolution was 33% after 56 days of incubation with an application of 1000 mg La/kg dry soil. The results in this paper indicated that agricultural use of REEs such as La at excessive levels would produce harmful effects to soil microbial activity and microbially mediated soil function. It is likely that change in soil dehydrogenase activity can be used as a sensitive indicator in assessing the level of REEs pollution in soil.
Soil nitrogen mineralisation changes rapidly when pine is planted into herbicide-treated pasture—the first two years of growth
Authors: Parfitt R. L. , Ross D. J. , Hill L. F.
Published: August 2003

The conversion of hill country pastures to exotic forest plantations has occurred rapidly in New Zealand over the last 10 years. This land-use change affects properties of the mineral soil, especially nitrogen (N) cycling. Here we studied the changes in soil in situ N mineralisation, in leaching, and microbial biomass, when Pinus radiata D. Don is planted into pasture; sheep were used to reduce pasture herbage before planting, and then herbicide was used to control the rank growth of grass around the trees. Total net N mineralisation in soil (0–100 mm) under pasture was 325 kg/ha.year. Net N mineralisation in the herbicide-treated areas was about double that under pasture or rank grass in the first 2 months. The concentration of nitrate-N in soil solution in the herbicide-treated areas was then 81 mg/L, compared with <2 mg/L under pasture. During this time, the pH under the pine trees decreased very rapidly as nitrification increased. Soil nitrification and nitrate leaching were enhanced for 15 months after application of herbicide. After this 15-month period, soil total carbon (C) was slightly lower (P < 0.10) under trees than rank grass, whereas microbial C and N were markedly lowest (P < 0.05) under the trees. Over this period, about 18 kg N/ha was leached to 250 mm in the tree-planted area. The data also give additional insights into processes that occur when soil cores in buried bags are used to estimate N mineralisation.
Volatilisation of nitrogen from land applied biosolids
Authors: Robinson M. B. , Röper H.
Published: August 2003

Volatilisation of nitrogen from biosolids applied to land reduces the amount of nitrogen available for plant uptake and contamination of groundwater. This study determined rates of volatilisation of ammonium-nitrogen from biosolids after surface-application in a mature pine forest. Biosolids from the Bromley Waste Water Treatment Plant in Christchurch, New Zealand, were applied at 2 rates under controlled conditions to exclude leaching and plant uptake. Volatilisation was calculated using a mass balance approach.
Despite climatic conditions apparently not suited to volatilisation, 44–55% of the ammonium-nitrogen applied in biosolids was volatilised. The majority of the losses occurred within about 1 day of application, and 95% of the losses occurred within 5 days. The losses represent about 12% of the total nitrogen applied, or about one-third of the 'plant-available' nitrogen. As volatilised nitrogen is not available for plant uptake or leaching to groundwater, volatile losses of nitrogen applied in biosolids need to be considered when calculating rates of biosolids application to protect groundwater while providing nutritional benefit.
Parameterisation of physically based solute transport models in sandy soils
Authors: Oliver Y. M. , Smettem K. R. J.
Published: August 2003

Immobile water fractions of up to 40% had been reported in sands, and it was therefore relevant to determine if the convection-dispersion equation (CDE) or mobile-immobile model (MIM) should be used as the basic physical model for field studies of solute transport in sandy soils. A review of literature data for granular media indicated that for steady state flow, the dispersion coefficient could be estimated from the grain Peclét number and the mass exchange coefficient from the pore water velocity, but the immobile water fraction was poorly predicted from soil properties.In this study, performed on a sandy soil at Moora, Western Australia, the choice of model was determined after analysis of column effluent breakthrough curves (BTC), sequential tracer experiments, and single tracer experiments on the same core. The latter two methods have recently been introduced in an attempt to independently measure some of the MIM parameters (immobile water content and mass transfer exchange coefficient) in situ. Low immobile water content was found in this sand, with very rapid exchange between the mobile and immobile regions. All 3 techniques gave measured immobile water contents around 10%, which was consistent with most literature values for granular media. The single tracer experiment does not give the mass exchange coefficient α (h–1), but α determined by the sequential tracer technique could not be confirmed by the BTC technique due to the wide 95% confidence interval of the fitted parameter. Although the MIM behaviour was minor and inconsistent in the Moora sand, the choice of model may depend on the problem under consideration. For short column experiments, the CDE and MIM produced similar solute transport behaviour. However, for leaching below the root-zone, the MIM is recommended.
Urea hydrolysis and inorganic N in a Luvisol after application of fertiliser containing rare-earth elements
Authors: Xu Xingkai , Wang Zijian , Wang Yuesi , Inubushi Kazuyuki
Published: August 2003

In recent decades, Chinese agriculturists have used rare-earth-containing fertilisers as basal fertilisers together with N fertilisers (e.g. urea). We studied urea hydrolysis and its hydrolysis products in a laboratory experiment using urea-N fertiliser with rare earths at rates from 0.5 to 50% (w/w). The results indicated that application of rare earths at a high rate could result in a short-term inhibition of urea hydrolysis and an increase in soil (NH4+ + NO3– + NO2–)-N content. When the application rate of rare earths was higher than 5% of the applied urea-N (corresponding to 10 mg/kg soil), soil exchangeable NH4+-N content increased significantly following the hydrolysis of the applied urea. Increasing the application rate of rare earths appeared to reduce the content of soil urea-derived (NO3– + NO2–)-N. A substantial reduction in soil pH was found immediately after application of rare earths and urea. We conclude that application of rare earths at >10 mg/kg may lead to a substantial increase in the content of urea-derived N in the soil, via the inhibition of urea hydrolysis and nitrification.
The determination of labile cadmium in some biosolids-amended soils by isotope dilution plasma mass spectrometry
Authors: Gray C. W. , McLaren R. G. , Shiowatana J.
Published: August 2003

An isotope dilution inductively coupled plasma-mass spectrometry (ICP-MS) technique, using an enriched stable Cd isotope, was applied to determine the labile fraction of Cd in 20 biosolids-amended soils. The measured labile Cd fraction was compared with the amounts of Cd solubilised or extracted by HNO3, EDTA, CaCl2, and Ca(NO3)2. Labile Cd, as a proportion of total soil Cd (% labile), ranged between 33 and 84% with a mean of 50%, indicating that a significant proportion of the Cd added to these soils from biosolids is in non-labile forms. EDTA was found to release Cd from non-labile sites, solubilising on average 30% more Cd than labile forms measured by isotope dilution. In contrast, the proportion of Ca(NO3)2-extractable Cd was significantly less than the measured labile fraction and probably represents Cd in soil solution. Extraction of soil with 1 M CaCl2, however, was found to provide a very good estimate of labile Cd in these biosolids-amended soils. Isotope dilution ICP-MS using an enriched stable Cd isotope and ICP-MS appears to be an analytical technique which has the potential to measure labile Cd in soils without the problems associated with the use of radioisotopes.
EC1:5/exchangeable Na, a sodicity index for cotton farming systems in irrigated and rainfed Vertosols
Authors: Hulugalle N. R. , Finlay L. A.
Published: August 2003

Sodic soils are characterised by their poor structural stability. This is thought to be caused mainly by high levels of exchangeable sodium and low electrolyte concentrations. Historically, soil sodicity has been reported as the exchangeable sodium percentage, ESP [(exchangeable Na/∑ exchangeable cations)�×�100]. However, some authors believe that exchangeable sodium content alone is a better indicator of sodicity, whereas others suggest that an effective sodicity index is one which includes both the exchangeable sodium levels and electrolyte concentration (EC1:5). Some examples are the electrochemical stability index (EC 1:5/ESP) and EC1:5/exchangeable Na. The objective of this study was to evaluate which of 3 empirical sodicity indices (ESP, EC1:5/ESP, EC1:5/exchangeable Na) was best related to soil dispersion in Vertosols sown to cotton farming systems.Soil was sampled between 1995 and 2001 from 4 irrigated and dryland sites in New South Wales and Queensland, where the cropping systems included continuous cotton (Gossypium hirsutum L.), cotton–rotation crop sequences, and 2- and 1-m beds. Tillage systems ranged from zero to minimum tillage. Soils from all sites were analysed for EC1:5, exchangeable Ca, Mg, K, and Na, and dispersion index, and ESP, EC1:5/ESP and EC1:5/exchangeable Na derived. Long-term dispersion was best predicted by EC1:5/exchangeable Na, except where zero tillage was practised when none of the sodicity indices were related to dispersion. Aggregate stabilisation under zero tillage was speculated to be determined largely by labile soil organic matter and microbial activity rather than sodicity.
Leaching of copper from contaminated soil following the application of EDTA. I. Repacked soil experiments and a model
Authors: Thayalakumaran T. , Vogeler I. , Scotter D. R. , Percival H. J. , Robinson B. H. , Clothier B. E.
Published: August 2003

The EDTA-enhanced remediation of copper contaminated sandy-loam soil of volcanic origin was investigated. The soil, from an orchard, was contaminated with about 250 mg/kg of copper due to the extensive use of copper sprays. Copper-contaminated soil was packed into 100-mm-long columns, and solutions of Na2H2EDTA with CaCl2, raised to a pH of 6.2, were applied at a flow rate of 24 mm/h. Application of an excess of 0.01 M EDTA leached about half the acid-extractable copper from the soil; most of it coming out in the first 3 liquid-filled pore volumes (PV). Also a 0.5 PV pulse of 0.001 M EDTA was applied to similar soil columns and then either leached immediately with 0.005 M CaCl2, or left for periods of up to 1 month before leaching. With immediate leaching, 70% of the EDTA applied was complexed with copper in the leachate, but after a month's delay only 24% was complexed with copper in the leachate, the rest being complexed with iron. There was no evidence of EDTA retardation or adsorption.
The experimental results were simulated using the convection–dispersion equation, incorporating a source/sink term. This described the competing time-dependent reactions of copper and iron with EDTA, and the reversion of CuEDTA2– to adsorbed Cu2+ and Fe(III)EDTA– in solution. Reasonable simulations were achieved, mostly within errors of observation.
Leaching of copper from contaminated soil following the application of EDTA. II. Intact core experiments and model testing
Authors: Vogeler I. , Thayalakumaran T. , Scotter D. R. , Percival H. J. , Robinson H. , Clothier B. E.
Published: August 2003

In Part I, we proposed a model for EDTA-facilitated transport of copper, and we tested the robustness of this scheme by reference to experiments with various initial and boundary conditions on a repacked soil. Now we examine a quite different repacked soil, and consider intact cores of the same soil as in Part I.
Continuous leaching of an intact core of a contaminated orchard soil of volcanic origin under unsaturated conditions with excess 0.01 M EDTA (510 mm) reduced the copper concentration from 240 down to 80 μg/g in the top 25 mm. When a 480 μmol pulse of 0.001 M EDTA was applied to similar intact cores, 126 μmol of copper came out with immediate leaching, but only 18% of that was leached out from a core that was left for 1 month before leaching. The month's delay caused an increase in the amount of iron leached from 116 to 286 μmol. An experiment, in which daily pulses CuEDTA2– were applied to a non-contaminated soil for 3 months, indicated that these changes were due to CuEDTA2– slowly changing to Fe(III)EDTA–, with the re-adsorption of the Cu2+ released.
Application of our model from Part I indicated that different rate constants are required for the chemical reactions for different soils, and also for the same volcanic soil when the pH is lower. But by changing just the dispersivity from 3 mm to 23 mm, the model with the same chemical parameters was able to simulate both the repacked columns and the intact core experiments using the volcanic soil.
Using quantity/intensity relationships to assess the potential for ammonium leaching in a Vertosol
Authors: Page K. L. , Menzies N. W. , Dalal R. C.
Published: August 2003

High concentrations of ammonium (up to 0.1 cmol/kg) have been observed below 1 m depth in a Vertosol soil near Warra in south-eastern Queensland. This study examined whether ammonium leaching could be responsible for the ammonium accumulation observed in the Warra soil. This was done by using quantity/intensity (Q/I) relationships to compare the ammonium retention capacity of the Warra soil with other similar soils throughout the region that did not contain elevated subsoil ammonium concentrations. Analysis of Q/I curves revealed that in the concentration range studied, the amount of ammonium retained on high affinity adsorption sites in all 3 soils was low, and the Warra soil was not significantly different from the other 2 soils. The ability of the soils to retain ammonium in the soil solution against leaching [i.e. their potential buffer capacity (PBC)] did differ between soils and was greatest at Warra. This indicates that at any one time the Warra soil holds more ammonium on the exchange complex and less in solution than the other soils examined. It was concluded that ammonium is no more likely to leach through the surface horizons of the Warra soil than the other soils examined. Indeed, the data indicated that the Warra soil probably has greater capacity to retain ammonium against leaching due to its greater PBC. Consequently, it is considered unlikely that leaching of ammonium has been a major contributor to the subsoil ammonium concentrations at Warra.
Contrasting behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in soil profiles
Authors: Baskaran S. , Kookana R. S. , Naidu R.
Published: August 2003

Regulatory agencies and natural resource managers are increasingly recognising the role of pesticide metabolites in the overall risk to non-target organisms. However, the environment fate data on pesticide metabolites are relatively meagre. We report the sorption and degradation behaviour of chlorpyrifos and its primary metabolite, TCP (3,5,6-trichloro-2-pyridinol), with depth in 2 Australian soil profiles. Sorption isotherms were determined by batch equilibrium method and the degradation was studied under controlled incubation conditions. Sorption of chlorpyrifos (Kd = 40.3–209.6 L/kg) was found to be about 100 times higher than that of TCP (Kd = 0.45–2.86 L/kg) in both the soil profiles. A significant correlation (r2�=�0.88**) was found between sorption of chlorpyrifos and the soil organic carbon content, but not in the case of TCP. However, in the case of TCP a significant inverse relationship was observed with pH (r2�=�0.81**). The rate of degradation of chlorpyrifos increased with depth in the soil profile, whereas the converse was true for TCP. The time for 50% loss of chlorpyrifos (DT50) was found to be 23–28 days in the surface soils (acidic pH) and only 7–16 days in the subsurface (alkaline pH). The DT50 values for TCP in the surface soils ranged from 42 to 49 days and in subsurface soils from 64 to 117 days. The contrasting behaviour of chlorpyrifos and TCP in soil profiles is clearly evident from the study. Due to its lower sorption and longer persistence, TCP has a much greater leaching potential than chlorpyrifos.
Tillage erosion intensity in the South Canterbury Downlands, New Zealand
Authors: Quine Timothy A. , Basher Les R. , Nicholas Andrew P.
Published: August 2003

Growing awareness of the pressure on land resources emphasises the need to understand the full range of processes operating in human-impacted agroecosystems. In such systems one of the greatest threats to long-term sustainability is the erosion and depauperation of soil, which, until recently, was attributed almost entirely to water erosion. This study builds on recent awareness of the significance of tillage erosion and presents the results of an experimental investigation of tillage erosion due to mouldboard ploughing. Aluminium cubes were used to trace soil translocation as a result of a single pass of the plough perpendicular to the contour in downslope and upslope directions. In common with others studies, translocation was found to be directly proportional to slope tangent for downslope tillage and unrelated to slope for upslope tillage. The influence of non-topographic variables on the relationship between translocation distance and slope was partially filtered out by using the ratio of translocation distances in the tillage direction and perpendicular to tillage. Shallow plough depths of 0.17 m produced tillage detachment of only 230 kg/m2; however, a high tillage translocation coefficient of 1.16 m/pass resulted in a soil flux coefficient of 265 kg/m.pass. The high tillage translocation coefficient is probably partly due to the loose nature of the regularly cultivated loessic soil, however, on the basis of comparison with other published studies, it is suggested that the high tillage speed of 7 km/h is the principal control on the magnitude of the coefficient. Analysis of the available data suggests that a 30% reduction in tillage erosion intensity could be obtained by reduction of the tillage speed to 4 km/h; nevertheless, more experimental work is needed to test this suggestion. On the transect studied, a pair of opposing passes of the mouldboard plough would produce erosion rates as high as 5.1 kg/m2.year (51 t/ha.year) from shoulder slope elements and as high as 1.9 kg/m2.year (19 t/ha.year) over half of the slope length. This pattern matched closely the distribution of 137Cs-derived erosion rates documented previously for a nearby field, suggesting that for this environment, as for many mechanised agricultural systems, tillage erosion is the dominant soil redistribution process and the greatest threat to long-term sustained on-site productivity. Reduction of tillage erosion should, therefore, be seen as a priority in the development of sustainable land management strategies.
Estimating nitrous oxide emissions from flood-irrigated alkaline grey clays
Authors: Rochester Ian J.
Published: August 2003

Concern has mounted over recent decades regarding the emission of nitrous oxide (N2O) to the atmosphere through human activities. Modern agriculture has contributed to this with elevated use of nitrogenous fertilizers and irrigation. Irrigated cotton grown on alkaline heavy clay soils often uses nitrogen fertiliser inefficiently, due largely to N loss (commonly 50–100 kg N/ha) through denitrification. However, the amount of denitrified N emitted as N2O has rarely been measured. This paper derives estimates of the quantities of N2O emitted from N fertiliser applied to alkaline grey clays.A negative exponential function between the N2O/N2 mole fraction and soil pH was derived from a search of laboratory and field studies published by numerous authors using a wide range of soil types. A greater proportion of N2O relative to N2 is emitted from acid soils; approximately equivalent amounts of each gas are emitted from soil of pH 6.0. For the alkaline grey clays (pH 8.3–8.5), the N2O/N2 mole fraction was about 0.024.The quantities of N2O emitted from alkaline grey clays during the growth of a cotton crop were estimated by applying this relationship to 15N balance studies where N fertiliser losses had been measured. Using this approach, about 2 kg N/ha (~1.1% of the N applied) was calculated to be lost as N2O during the cotton-growing season. This is similar to the value of 1.25% commonly used to estimate N2O emissions from N fertiliser, but this estimation should only be applied to alkaline soils; a larger percentage of the fertiliser N denitrified from acid soils should be emitted as N2O-N. These estimates of N2O emissions require validation with field experimentation.The low (negligible) values for N2O emission from flooded fields compared with laboratory observations are discussed. It is possible that high N2O emissions observed under laboratory conditions result from the shallow depth of soil, reducing the opportunity for N2O to be further reduced as it diffuses through the soil profile. Management strategies that have the potential to reduce N2O emissions are discussed.
Particle-size distribution of soil and the perception of texture
Authors: Marshall T. J.
Published: August 2003

It has been suggested in this journal that, for uniformity, the texture diagram of the United States Department of Agriculture could be adopted in Australia. However, it is argued here that the Australian diagram should be retained because of the advantages given by its more systematic set of class limits with smooth transitions between classes, and its use of sloping, rather than horizontal, lines for clay content. This sloping trend accords with the behaviour of soil when tested for texture in the field. The principles underlying these features are discussed.Changes to the USDA diagram have brought it closer to the Australian diagram. The Australian diagram is unchanged but the fraction sizes chosen for it have been criticised. Raising the upper limit of the silt fraction from 20 μm to 50 μm would make its fractions uniform with those of the USDA. It would also double the average silt content and so give a better spread of texture classes. The diagram can be converted without losing its design advantages or changing its texture standards.
The influence of low rates of air-dried biosolids on yield and phosphorus and zinc nutrition of wheat (Triticum durum) and barley( Hordeum vulgare)
Authors: Weggler-Beaton Karin , Graham Robin D. , McLaughlin Michael J.
Published: August 2003

In field studies in 1992 and 1993, biosolid applications of 2 t/ha with supplements of mineral N and P were compared with a standard mineral fertiliser application (20 kg N/ha, 20 kg P/ha, 1.8–2.8 kg Zn/ha, 1.4–1.9 kg Cu/ha, 0.5–4 kg Mn/ha) on 4 soil types. Biosolid rates from 2 to 10 t/ha were applied in 1993. Shoot dry matter production at different stages of plant development (9 and 15 weeks after sowing) and grain production of Triticum durum and Hordeum vulgare, as well as nutrient concentration in shoots and grain, were taken as indicators for comparing nutrient availability of the 2 sources. A 2-t biosolid application was found to enhance dry-matter production and yield to the same extent as a mineral fertiliser application of 20 kg N/ha, 20 kg P/ha, and 1.8–2.8 kg Zn/ha. In some crop rotations and on sites with a high yield potential, additional nitrogen with 2 t biosolids/ha would be necessary to achieve such yields. However, development of durum wheat fertilised with 2 t biosolids was slower and P uptake lower than with mineral fertiliser until late booting. Durum wheat fertilised with 4 t biosolids showed similar P-uptake values as plants fertilised with the mineral fertiliser. The Zn-uptake of plants was positively correlated with biosolid application rates, showing a linear relationship. A 2-t biosolid application alleviated micronutrient deficiency to the same extent as the same rate of Zn (and Cu) given in mineral form.
Increased P application to lateritic soil in 1976 increased Colwell soil test P for P applied in 2000
Authors: Bolland M. D. A. , Allen D. G.
Published: August 2003

In a field experiment, 6 amounts of superphosphate [0–800 kg phosphorus (P)/ha] were applied in July 2000 to an acidic lateritic ironstone gravel sandy soil treated 24 years previously (May 1976) with 6 amounts of superphosphate (0–599 kg P/ha). In October 2001, samples of the top 10 cm of soil were collected to measure the capacity of the soil to sorb P by the phosphate retention index (PRI) and P buffer capacity (PBC) methods, and to measure soil test P by the Colwell (sodium bicarbonate) procedure. The capacity of the soil to sorb P, as measured by both PRI and PBC, decreased with increased P application in 1976. For all amounts of P applied in 2000, Colwell soil test P increased with increased P application in 1976. We conclude that increasing amounts of P applied in 1976 decreased the capacity of the soil to sorb the subsequent application of P, thereby increasing soil test P values of soil treated with the subsequent P.
Can liming mitigate N2O fluxes from a urine-amended soil?
Authors: Clough T. J. , Sherlock R. R. , Kelliher F. M.
Published: August 2003

Soil pH affects N2O production mechanisms. The ratio of N2O to N2 may decrease with increasing soil pH during denitrification. Two laboratory experiments were performed to examine the effect of liming on N2O emissions following synthetic urine applications over 42 and 60 days. A silt loam soil at field capacity (water-filled pore space of 57% after treatment application) was adjusted with Ca(OH)2 to produce soils ranging from pH 4.7 to 7.7. The first experiment employed 4 treatments: a control, KNO3 (500 kg N/ha), and synthetic urine at 500 kg N/ha and 1000 kg N/ha. A second experiment used 15N labelled urea in synthetic urine at 500 kg N/ha. The main effect of lime was to promote nitrification, which markedly affected N2O fluxes. After 60 days, the 500 kg N/ha synthetic urine treatment limed to pH 6.1 produced more N2O (0.82% of N applied) than any other soil pH. No optimum soil pH was found for the synthetic urine treatment at 1000 kg N/ha with nitrification incomplete after 60 days. N2O production via nitrifiers dominated the N2O production pathway with large residual NO3– pools. Denitrification was not enhanced since no 15N labelled N2 was detected. However, before any final conclusions can be drawn about the efficacy of liming as a mitigation tool it is vital that the effect of liming on possible denitrification mechanisms and products also be assessed, following nitrification and formation of a nitrate pool. Application of synthetic urine also initiated a priming effect with more carbon evolved as CO2 than was applied.
Relative effect of climate, soil, and management on risk of nitrateleaching under wheat production in Canterbury, New Zealand
Authors: Lilburne L. R. , Webb T. H. , Francis G. S.
Published: August 2003

The GLEAMS simulation model was used to determine the relative effects of climate (19 years of data), soil type (4 soils distinguished by effective soil depth), and farm management (6 sowing dates and 5 levels of nitrogen fertiliser) on leaching of nitrate under wheat production. All combinations of inputs were simulated and the effects of each input were estimated with sensitivity analysis software (SimLab). Soil type, climate, and sowing date explained about equal amounts of the variance in nitrate leaching, whereas fertiliser application explained only about one-third of the variance of the other inputs. The 2 most significant results were: (1) the importance of having plant uptake of nitrogen during autumn and winter to limit nitrate availability for leaching, and (2) the recognition that leaching of nitrate becomes increasingly sensitive to farm management practices with decreasing soil depth. The risk of nitrate leaching was found to be very low on deep soils when the crop was sowed in the autumn or winter. These results help with identifying areas where management changes might be effective in reducing the long-term risk of nitrate leaching. Crop growth over winter and judicious use of fertiliser are particularly recommended for cropping on shallow soils.
The influence of cutting and grazing on phosphorus and nitrogen in irrigation runoff from perennial pasture
Authors: Mundy G. N. , Nexhip K. J. , Austin N. R. , Collins M. D.
Published: August 2003

Runoff from flood-irrigated perennial pastures generally contains higher phosphorus (P) and nitrogen (N) concentrations than the irrigation water applied to the pastures. We examined the sources of P and N that could contribute to these elevated nutrient concentrations in runoff.The first experiment compared P and N losses in runoff from pasture cut to different residual pasture masses. Flow-weighted P and N concentrations and loads were about 100% higher from pasture cut to 47�mm above ground than from pasture standing at 155 mm. These results indicated that severely defoliated pasture may be a significant source of nutrients when flood irrigated.In the second experiment, pastures were defoliated at a single grazing with different stocking intensities and the flow-weighted P and N concentrations in runoff were determined during 4 successive flood irrigation events. Nitrogen and P concentrations in runoff after the first irrigation following defoliation were higher at the highest stocking intensity. However, the effect of the grazing on nutrient concentrations in runoff declined in subsequent irrigation events. A regression model fitted to the P data indicated that there was a significant linear increase in P concentrations with stocking density and a significant non-linear decline in concentrations with successive irrigations. A similar relationship for TKN concentrations in runoff at each stocking density over the 4 irrigation events was not found. An inconsistency of the TKN concentrations of the supply water between irrigation events possibly helped to mask a similar relationship between N concentrations in runoff and stocking density over the 4 irrigation events. We postulate that both animal excreta and the pasture itself can contribute to elevated nutrient concentrations in flood-irrigation runoff.
Leaching of macronutrients and metals from undisturbed soils treated with metal-spiked sewage sludge. 1. Leaching of macronutrients
Authors: McLaren R. G. , Clucas L. M. , Taylor M. D. , Hendry T.
Published: August 2003

The extent of macronutrient leaching from soils treated with sewage sludge has been examined using large undisturbed soil lysimeters of 5 different New Zealand soils (2 pasture and 3 forest soils). Nutrient leaching from the soils was monitored continuously over a period of 3 years following a single application of sewage sludge. Application of sewage sludge resulted in increased concentrations and total amounts of SO42–, NO3–, Ca, Mg, Na, and K in drainage leachates, but had little effect on Cl– and dissolved organic carbon concentrations. The quality of the analytical data in the study (several hundred individual analyses) was confirmed by the excellent charge balance between the main anions and cations in the leachates. The peaking of some cation and anion concentrations well before 1 pore volume of water had passed through the lysimeters indicated that macropore flow could be an important process facilitating nutrient leaching. However, the extent of anion and cation leaching varied greatly between soils and appeared dependent on a number of soil properties and other factors. For example, the amount of drainage and the presence of growing plants clearly had a marked effect on the extent of macronutrient leaching, as did the way in which the sludge was applied to the soil. Sulfur (as SO42–) was the dominant anion and Na+ the dominant cation leached, but concentrations of both these nutrients in the sludge used for this study were higher than would normally be expected in New Zealand sludges. The effect of sludge application on Mg2+ leaching was particularly interesting, in that the high Ca : Mg ratio of the sludge appeared to promote the leaching of native Mg from the soil.
Risk assessment of phosphorus loss from sugarcane soils — A tool to promote improved management of P fertiliser
Authors: Bramley R. G. V. , Roth C. H. , Wood A. W.
Published: August 2003

Current strategies for phosphorus (P) fertiliser management in the Australian sugar industry do not account for the differences between different soils in their ability to sorb and release P. However, the off-site export of P from land under sugarcane has been shown to be a major factor contributing to elevated concentrations of P in stream waters draining catchments dominated by sugarcane production. This paper presents the results of a study conducted in the lower part of the catchment of the Herbert River, north Queensland, a major sugarcane growing region. Our approach was to combine a knowledge of P sorption by soil and riverine sediments with an assessment of the risk of P loss from lower Herbert sugarcane soils and knowledge of the requirements of sugarcane for P. The results provide a basis for future P fertiliser management by canegrowers which accounts for both production and environmental imperatives. They also point to an urgent need for experimentation, based on rundown of soil P fertility, to determine critical soil test values in soils of varying P sorption, and provide a useful regional framework for the design of such experimentation.
Nitrate ammonification and its relationship to the accumulation of ammonium in a Vertisol subsoil
Authors: Page K. L. , Dalal R. C. , Menzies N. W.
Published: August 2003

High concentrations of ammonium (up to 270 kg N/ha) have been observed in a Vertisol soil below 1 m depth near Warra in south-east Queensland. This study examined the possibility that increased water movement into the subsoil after the removal of native vegetation, and a subsequent increase in periods of waterlogging, could have triggered nitrate ammonification and be responsible for the production of ammonium. Two incubation experiments were conducted to test this hypothesis. The first involved the incubation of repacked cores that had been amended with 30 mg N/kg of 5 atom% 15N nitrate under low oxygen conditions for a period of 360 days. Over this time period the 15N enrichment of the exchangeable ammonium fraction was monitored in order to detect any reduction of nitrate to ammonium. The second experiment involved the incubation of soil amended with 30 mg N/kg of 5 atom% 15N nitrate under waterlogged and low oxygen conditions for 75 days. During this period the redox potential of the soil was monitored using a field test to determine if reducing conditions would develop in this soil over a period of waterlogging, combined with the monitoring of any nitrate reduction to ammonium. The results of these experiments indicated that a small amount of nitrate ammonification (<0.1 mg N/kg) could be observed in the Warra subsoil, but that unless the rate of reduction were to significantly increase with time, this could not account for the accumulation of ammonium observed in the field. The environmental conditions that would make either dissimilatory or abiotic nitrate ammonification favourable were not observed to develop. Consequently, it has been concluded that the observed nitrate ammonification occurred via an assimilatory pathway. Due to the low rate of microbial activity in this subsoil it is considered unlikely that this process was responsible for the subsoil ammonium accumulation at Warra.
N2O and N2 gas fluxes, soil gas pressures, and ebullition events following irrigation of 15NO3 - -labelled subsoils
Authors: Clough T. J. , Rolston D. E. , Stevens R. J. , Laughlin R. J.
Published: August 2003

We examined the fate of N2O following the addition of labelled nitrate and subsequent irrigation. Repacked silt loam soil columns, 1 m deep, were wetted up and instrumented with pressure transducers, soil profile gas samplers, and time domain reflectometry rods. Combined substrates (glucose- and 15N-enriched nitrate) were injected at 0.45 m depth. N2O, N2, and NO were monitored in the soil profile and headspaces. When soil profile N2O gas concentrations became elevated, an irrigation event was applied. Immediately prior to the irrigation event, confined drainage (no drainage outlet) and unconfined drainage (lateral drainage outlet at 0.9 m depth) treatments were implemented. Soil profile gas pressures increased following irrigation with pressure changes at 0.375 m chronologically linked to increased pressure pulses in the headspace. Irrigation contributed to decreases in N2O gas concentrations in the soil profile. N2O and N2 displaced in drainage from the unconfined treatment represented 0.01 and 2.3% of the gas in the soil profile immediately prior to irrigation, respectively. Following irrigation, soil gas pressures increased to a maximum of 11.8 kPa at 0.825 m soil depth in the confined drainage treatment but only reached 4.3 kPa at the same depth in the unconfined drainage treatment. It is suggested that ebullition events could possibly contribute to the increased and variable fluxes of N2O, commonly observed, immediately following rainfall or irrigation.
Emission of nitrogen oxides and ammonia from varying rates of applied synthetic urine and correlations with soil chemistry
Authors: Clough T. J. , Sherlock R. R. , Mautner M. N. , Milligan D. B. , Wilson P. F. , Freeman C. G. , McEwan M. J.
Published: August 2003

Synthetic urine was applied at 5 rates, from 0 to 1000 kg synthetic urine-N/ha, to a pasture soil under controlled laboratory conditions. Gaseous emissions of NOx and NH3 were monitored for up to 21 days following application using selected ion flow tube mass spectrometry with N2O measured using electron-capture gas chromatography. During this period soil replicates were destructively sampled to measure changes in soil pH and inorganic-N concentrations. Comparisons were made between measured soil variables, calculated soil concentrations of NH3(g), HNO2, and the measured gas fluxes. At N rates up to 500 kg N/ha, inorganic-N concentrations increased as nitrification progressed over time. With the exception of the 1000 kg N/ha treatment, NO production followed the pattern of increasing nitrification, reaching a maximum of 905 ng NO-N/cm2.h in the 500 kg N/ha treatment 14 days after synthetic urine application. At this time the NO flux was associated best with soil pH, NH4+, and NO2– levels. Over 21 days the maximum cumulative loss as NO-N and N2O-N occurred under the 100 kg N/ha urine treatment, with 6.6 and 6.4% of N applied lost as gas, respectively. NO2 gas fluxes paralleled the NO emissions but were an order of magnitude smaller. Nitrification was inhibited in the 1000 kg N/ha treatment due to the sustained high ammoniacal-N and pH conditions present. These conditions prolonged the NH3 volatilisation from this treatment. NH3 volatilisation, as determined by selected ion flow tube-mass spectrometry, was linearly related to calculated soil NH3 gas concentrations up to 500 kg N/ha on Day 1.
Soil properties as predictors of yield response of clover (Trifolium subterraneum L.) to added P in soils of varying P sorption capacity
Authors: Brennan R. F. , Bolland M. D. A.
Published: August 2003

Thirty-five unfertilised soils collected in south-western Australia were used to measure the effect of soil properties on (i) shoot yield responses of 50-day-old clover (Trifolium subterraneum L. cv. Nungarin) plants to applied phosphorus (P), and (ii) extractability of bicarbonate soil test P (slope of the linear relationship between Colwell P and the amount of P applied). Data for the relationship between shoot yield and the amount of P applied were fitted to a rescaled Mitscherlich equation to calculate the amount of P required to produce 50% and 90% of the maximum yield (P50% and P90%) and determine the curvature (c) and n coefficients of the equation. When the value of n is 1.00, the response curve is exponential, and as the value of n increases above 1.00 the response curve becomes more sigmoidal. The c, n, P50%, P90%, and extractability values were related to properties of the 35 soils.There was a significant (P < 0.05) trend for the values of c and extractability to decrease as the capacity of the soil to sorb P increased. Consequently, as the soil sorbed more P, the trend was that (1) more P needed to be applied to produce the same yield, so both P50% and P90% tended to significantly (P < 0.05) increase; (2) shoot yield responses to applied P became more sigmoidal so the value of the n coefficient tended to significantly (P < 0.05) increase; (3) more P needed to be applied to a soil to produce the same soil test P value; and (4) larger soil test P values were needed to produce the same yield. No single soil property adequately predicted P50%, P90%, extractability, c, or n. Stepwise multiple regression indicated that (1) clay content and P buffer capacity (PBC) of soil together accounted for 48% of the variation in P50%, 56% of the variation in P90%, and 52% of the variation in c; (2) PBC and soil pH together accounted for 17% of the variation in n; and (3) PBC, percentage clay and percentage organic carbon content of soil together accounted for 68% of the variation in extractability.
The relationship between animal foraging and nutrient patchiness in south-west Australian woodland soils
Authors: Garkaklis Mark J. , Bradley J. S. , Wooller R. D.
Published: August 2003

The woylie (Bettongia penicillata) was once common and abundant over the southern third of the Australian continent. Since European settlement the range of this rat-kangaroo has become reduced by more than 97%, and until the early 1990s, only 3 small natural populations remained, all in south-western Australia. These medium-sized (c. 1 kg) marsupials create a large number of diggings as they forage for the hypogeous fruiting bodies of ectomycorrhizal fungi upon which they feed. The effect of such foraging activity on the availability of plant nutrients in the vicinity of such diggings was evaluated in simulated digging experiments. Available nitrate, ammonium, and sulfur decreased significantly 3 years after diggings were constructed and had filled in, whereas phosphorus, potassium, iron, and organic carbon remained unchanged. The results suggest that preferential water infiltration via woylie diggings leads to a decrease in those soil nutrients that are susceptible to leaching and indicates that digging vertebrates may influence the distribution of surface soil nutrients.