bluuebunny/crossref_metadata_2025_split huggingface dataset:
An image analysis evaluation of soil compaction in grassland
Authors: KOPPI A. J. , DOUGLAS J. T. , MORAN C. J. 
Published: July 2006

SUMMARYIn the fifth year of a traffic management experiment on grassland comparing conventional (C), reduced ground pressure (R) and zero (Z) systems, differences in soil structure were characterized in the upper 100 mm. Soil bulk density and vane shear strength increased between systems in the order Z, R, C. A more detailed description of the soil structural differences between traffic systems, and between depths within systems, was obtained by an image‐interpretation technique. Rapid‐hardening epoxy resin, containing fluorescent dye, was added to the soil in the field condition, and the macroporosity was quantified by image analysis. All measured attributes (bulk density, vane shear strength and those from image analysis) showed that soil structure was superior in the zero (Z) and reduced ground pressure (R) traffic systems compared to that of the conventional (C) system. Porosity and pore or solid surface area of the Z system were greater, and aggregate size was smaller, than in the C system. In general, R was intermediate between Z and C. At about 10–30 mm in the reduced ground pressure system, there was a zone of low porosity that resembled much of the soil in the conventional system. Macroporosity and roots were concentrated close to the soil surface under the C and R systems. In the absence of traffic, or under the R system, the surface of the ground was rougher than that under the C system.
Carbendazim adsorption on montmorillonite, peat and soils
Authors: CANCELA G. DIOS , TABOADA E. ROMERO , SÁNCHEZ‐RASERO F. 
Published: July 2006

SUMMARYThe adsorption of carbendazim by peat and montmorillonite was studied as a function of the exchangeable cations and temperature. The adsorption on soils was also studied.The kinetics of carbendazim adsorption on peat showed that adsorption equilibrium was reached within 1 h. The order of adsorption of carbendazim on peat was as follows: H+‐peat > Cu2+‐peat > Co2+‐peat > Mg2+‐peat > K+‐peat, and the thermodynamic parameters appeared to suggest an adsorption mechanism involving hydrogen bonds, although in the H+, Cu2+ and Co2+ samples a protonation process and adsorption of the protonated species were also likely.The kinetics of carbendazim adsorption on montmorillonite (mont.) showed that equilibrium was reached within 1 h. The order of adsorption was: H+‐mont. > Cu2+‐mont. > Co2+‐mont. > Ca2+‐mont., the adsorption on the H+ and Cu2+ samples being much greater than that on the other samples. For the H+ and Cu2+ samples, the thermodynamic parameters appeared to suggest a double mechanism: physical adsorption, and protonation and adsorption by ion exchange. The most probable mechanism for the adsorption of carbendazim on the Co2+ and Ca2+ samples was physical bonding.The capacity for adsorption of this fungicide on soil was dependent on the organic matter, nitrogen and clay content, as well as on the cation exchange capacity. No significant correlation was found with pH, C/N ratio or free iron content.
Sample adequately to estimate variograms of soil properties
Authors: WEBSTER R. , OLIVER M. A. 
Published: July 2006

SUMMARYThe variogram is central in the spatial analysis of soil, yet it is often estimated from few data, and its precision is unknown because confidence limits cannot be determined analytically from a single set of data. Approximate confidence intervals for the variogram of a soil property can be found numerically by simulating a large field of values using a plausible model and then taking many samples from it and computing the observed variogram of each sample. A sampling distribution of the variogram and its percentiles can then be obtained. When this is done for situations typical in soil and environmental surveys it seems that variograms computed on fewer than 50 data are of little value and that at least 100 data are needed. Our experiments suggest that for a normally distributed isotropic variable a variogram computed from a sample of 150 data might often be satisfactory, while one derived from 225 data will usually be reliable.
Changes in soil solution composition and pH in urine‐affected areas of pasture
Authors: HAYNES R. J. , WILLIAMS P. H. 
Published: July 2006

SUMMARYChanges in soil solution composition and concentrations of exchangeable cations and mineral N in undisturbed cores of pasture soil were investigated in two experiments following applications of sheep urine to the cores. The major cations applied in the urine were K+ and Na+, and the major anions were HCO3− and Cl−. Addition of urine increased concentrations of exchangeable K+, Na+ and NH4+ and measured ionic strength of the soil solution throughout the surface 15 cm of soil, demonstrating that the urine moved through the core by macropore flow immediately following addition. Immediately following urine application the ionic strength in soil solution in the surface 2.5 cm of soil increased from 4–6 MM to 24–41 mM.Hydrolysis of urine‐urea was extremely rapid, and in less than 1 d high concentrations of NH4+‐N (i.e. 270–370 mg N kg−1) had accumulated in the surface 0–2.5 cm of the urine patch, and soil pH had risen by over one unit. Nitrification then proceeded and, after approximately 15 d, NO3− became the dominant form of mineral N present. During nitrification, soil pH declined and the ionic strength of the soil solution increased substantially with NO3− becoming the dominant anion present in solution. There were concomitant increases in the concentrations of Ca2+ and, to a lesser extent, Mg2+ in the soil solution as NO3− concentrations increased. After approximately 30 d, concentrations of exchangeable NO3− had risen to 250–330 mg N kg−1, soil solution NO3− concentrations had increased to about 80 mmol, dm−3, and ionic strength in the soil solution had increased to 130–140 mM. These results demonstrate the dominating effect of N transformations in causing large fluctuations in the pH, ionic composition and ionic strength of the soil solution in the urine patch. It was concluded that nutrient availability in the patch was affected directly by nutrient addition in urine, and also probably indirectly through the fluctuations in soil solution pH and ionic strength that occur.
Composition of carbon fractions and potential denitrification in drained peat soils
Authors: JÖRGENSEN R. G. , RICHTER G. M. 
Published: July 2006

SUMMARYThe organic matter of five low‐moor peat soils and one eutrophic raised‐bog peat soil was chemically characterized by C fractionation and ion‐exchange chromatography of amino acids and carbohydrates. C fractions were related to potential denitrification, Dpot, as a measure of microbial activity and C availability, determined by the acetylene inhibition technique. Chemical and physical properties vary distinctively between different kinds of peat, and show increasing C/N ratio and decreasing bulk density and ash content within the profile. Generally, the carbon composition reflects the geobotanical origin of the peat. In most samples more than 65% of organic C consists of non‐hydrolysable C. Readily hydrolysable neutral sugar C represents up to about 12% of organic C, usually decreasing with depth. The recalcitrant fraction of neutral sugar C is much smaller (1 to 4.2% of organic C) and does not vary with depth. The content of readily hydrolysable glucose exhibits a strong profile differentiation that decreases with depth, whereas the higher contents of recalcitrant glucose carbon (12/0.5 M H2SO4) in the lower peat horizons reflect their cellulose character. Regression analysis between Dpot and single C components explains up to 51.5% of the variability. Combining fractions which point to C availability (readily hydrolysable glucose) and microbial metabolism (amino acids), it is possible to estimate Dpot with a certainty of more than 80%.
Changes in microstructure of soils following extraction of organically bonded metals and organic matter
Authors: WIERZCHOS J. , CIRIA C. ASCASO , GARCIA‐GONZALEZ M. T. 
Published: July 2006

SUMMARYThe influence of selective removal of organically bonded metals and organic matter on soil microstructure was investigated. Two samples of soils with different mineralogical, chemical and mechanical composition were treated with acetylacetone in both polar and non‐polar solvents to dissolve amorphous organic iron and aluminium, and with hydrogen peroxide to destroy organic matter.Transmission electron micrographs of ultrathin sections and scanning electron micrographs of <5−μm fractions of the extracted soils showed distinct changes of microstructure of clays after successive removal of cementing agents. Although untreated soils showed flocculent or honeycomb structure, soils with organic matter and organically bonded metals removed showed turbostratic domain structure with stepped clusters. The changes in microstructure of soils following extraction were confirmed by determination of pore‐size distribution and total cumulative volume of pores using the mercury porosimetry method. In addition, the surface area of the extracted soils was determined by water adsorption. The results showed that organically bonded iron and aluminium and organic matter distinctly influence the fabric of microstructure as flocculating agents.
Geostatistical analysis of cyst nematodes in soil
Authors: WEBSTER R. , BOAG B. 
Published: July 2006

SUMMARYThe numbers of cyst nematodes that live in agricultural soil vary both in time and space with important consequences when devising procedures for inspection and strategies for their control. We have examined the distributions of two species, Globodera rostochiensis and Hererodera avenue, in fields in the east of Scotland by counting their live cysts in the topsoil. Nested sampling and analysis showed that most of the spatial variation occurs within distances of 5 m to 50 m. Experimental variograms computed from transects and grid surveys appeared to be isotropic and bounded with a range of approximately 60 m. Both species are strongly aggregated. H. avenue occurred in large patches. Indicators for cyst counts of 1, 4 and 10 were created from the data. The experimental auto and cross variograms of these indicators were computed and models fitted to them. All of these variograms had the same spherical form as that of the original counts but shorter ranges, and the cross variograms had more structure, suggesting a border effect. Biologically, the distribution can be explained by the nematodes being spread by cultivation from initial fortuitous foci of infestation or control by nematophagous fungi or both.
Properties of soil kaolinites from south‐western Australia
Authors: SINGH B. , GILKES R. J. 
Published: July 2006

SUMMARYThe clay fraction of soils from south‐western Australia is dominated by kaolinite. These soil kaolinites give broad basal reflections (median value for WHH 001 =0.41° 2θ) and have poorly ordered structures. The median value of the Hughes & Brown crystallinity index for 35 soil kaolinites is 5.4 compared to 42.0 for mineral standard kaolinites. The median values for surface area and cation exchange capacity of soil kaolinites are 35 m2 g−1 and 56.7 mmolc kg−1, respectively, compared to 10 m2 g−1 and 4.8 mmolc kg‐ l for standard kaolinites. The dehydroxylation temperature of soil kaolinites is about 50 K lower than for standard kaolinites and decreases with increasing Fe content.Soil kaolinite crystals are much smaller (c. 0.10 pm) and are irregular subrounded to rounded plates in comparison to the larger (c. 0.28 pm), perfectly hexagonal euhedral plates of Georgia kaolinite. Analytical electron microscopy of single soil kaolinite crystals indicates that the Fe content varies with an average value of c. 2.5% Fe,2O3. X‐ray diffraction line broadening data indicate that crystal size decreases as the Fe content increases. Crystal order also decreases with increasing Fe content. The P sorption maximum of soil kaolinite ranges from 486–654 μg P g−l and is thus about six times larger than for the clay fraction of Georgia kaolinite.
Computer simulation of metal ion—humic and fulvic acid interactions
Authors: MOUNTNEY A. W. , WILLIAMS D. R. 
Published: July 2006

SUMMARYThe humate model, RANDOM, was investigated in combination with the general speciation program, PHREEQE. After an initial investigation of cobalt(II)–humic acid and copper(II)–fulvic acid interactions this coupled code approach was modified to include a sensitivity analysis which identified the ligands which were statistically significant in any one system. Subsequent speciation modelling with these significant ligands is shown to produce a reasonable agreement between experimental and modelled data. The systems chosen to demonstrate the advantages of this approach were uranyl–humate and nickel(II)–humate interactions. Although this technique is not fully developed, it shows great potential for improving the predictive qualities of the RANDOM model.
The effect of pH on zinc adsorption by a lateritic soil in the presence of citrate and oxalate
Authors: CHAIRIDCHAI P. , RITCHIE G. S. P. 
Published: July 2006

SUMMARYA change in the pH of the rhizosphere may alter the effect that organic ligands have on the concentration of Zn in the soil solution. To assess this effect, Zn adsorption by a lateritic soil was measured in the presence of 0, 1 and 3 mM of citrate and oxalate at nine values of pH ranging from pH 2 to 8. The concentrations of Zn and the ligands remaining in the solution were determined after 17 h shaking with the soil at soil:liquid ratio of 1:5. Subsequently, Zn speciation was calculated. The effectiveness of an organic ligand (L) in changing Zn adsorption was influenced by the sign of the charge of the Zn‐L complex, the point of zero salt effect (PZSE) of the soil, the pH of the soil solution and the quantity of the complex formed. When the pH was above the PZSE of the soil, citrate decreased Zn adsorption by up to 38% whereas it increased Zn adsorption by as much as 51 % when the pH was below the PZSE. Oxalate had a similar but smaller effect than citrate under the conditions of the experiment. Zn adsorption was correlated with the concentration of zinc citrate in both pH regions (r2>0.98) and with oxalate above pH 2.7. The increase in Zn adsorption at low pH could have been caused by the adsorption of negatively charged Zn‐L complexes.
The reaction between phosphate and dry soil. II. The effect of time, temperature and moisture status during incubation on the amount of plant available P
Authors: BRAMLEY R. G. V. , BARROW N. J. 
Published: July 2006

SUMMARYSubterranean clover was grown in pots in which the only source of phosphate (P) was from bands of soil which had been incubated with P for a range of times, and at different temperatures, when either moist or air‐dry. The effectiveness of these incubated soils in supplying P to plants decreased with time of incubation. Effectiveness decreased after air‐dry incubation, though not as quickly as after moist incubation.These results indicate that air‐dry storage of soil samples is to be avoided if the samples are to be assessed for their ability to supply P to growing plants. They also indicate that the cost‐saving to Australian farmers, derived from applying phosphate prior to the start of the growing season, may be balanced or even outweighed by a loss in fertilizer effectiveness due to the reaction between P and the soil in the weeks prior to germination of seed.
Temporal variation in the hydraulic conductivity of a tilled clay soil as measured by tension infiltrometers
Authors: MESSING I. , JARVIS N. J. 
Published: July 2006

SUMMARYSteady‐state infiltration rates from tension infiltrometers were measured on ploughed and unploughed plots in a clay soil during the period June to October. Measurements were made both at the soil surface and at depths of 15 and 25 cm. Hydraulic conductivity in the water potential range zero to −11 cm was obtained using a piece‐wise exponential K(Ψ) function and Wooding's solution for infiltration from a circular source. A two‐line regression model showed excellent fits to paired (In KΨ) values on all measurement occasions. This may indicate the existence of a bimodal pore system, reflecting the contributions of macro‐ and mesopores to the measured K(Ψ) function. The break‐point potential dividing the two pore systems varied between c.−4 and −6cm. Significant variations in the K(Ψ) function between sampling occasions were found at the soil surface, but not at depths of 15 and 25 cm. Measured K(Ψ) values decreased during the growing season, particularly at potentials between −4 and −6 cm where reductions were up to one order of magnitude. This was attributed to soil structural breakdown by rain impact and surface capping or sealing. Hydraulic conductivity near the soil surface was significantly increased by disc harrowing in autumn. In contrast, no pronounced difference in the K(Ψ) function between ploughed and unploughed treatments could be discerned at 15 and 25 cm depths in the soil.
Losses of nitrate‐nitrogen in water draining from under autumn‐sown crops established by direct drilling or mouldboard ploughing
Authors: GOSS M. J. , HOWSE K. R. , LANE P. W. , CHRISTIAN D. G. , HARRIS G. L. 
Published: July 2006

SUMMARYThe leaching of nitrate‐N under autumn‐sown arable crops was measured using hydro‐logically isolated plots, about 0.24 ha in area, from 1984–1988. Fluxes of water and nitrate moving over the soil surface (surface runoff), at the interface between topsoil and subsoil (interflow), and in the subsoil (drainflow) were monitored in plots with mole‐and‐pipe drain systems (drained plots); surface runoff and interflow only were monitored in ‘undrained’ plots. Half the drained and undrained plots were direct‐drilled, and on the other half seedbeds were prepared by tillage to 200 mm. Tillage increased the total leaching loss of nitrate by 21 % compared with direct drilling in drained plots. About 95% or the nitrate moving from the soil was present in the water intercepted by the subsoil drains in these plots. In undrained plots less water and nitrate were collected in total; more of the nitrate was present in interflow on ploughed plots and in surface runoff in direct‐drilled land.Losses of nitrate for the whole experiment from 1978‐1988 were analysed. This showed that, between the harvest of one crop and the spring application of fertilizer to the next, loss of nitrate‐N from ploughed land (Lp) was approximated by Lp=22+Fkg N ha−1, where F was the autumn fertilizer‐N applied. After fertilizer was applied in spring, loss of nitrate‐N depended on rainfall such that for 100 mm rainfall about 30% of the fertilizer‐N was lost by leaching. About 18% more nitrate‐N was lost from direct‐drilled land than from ploughed land in spring, but the total loss was generally small compared to that over winter.The apparent net mineralization of organic‐N was measured in 1988. In autumn and winter there was little effect of tillage treatment (26 and 31 kg N ha−1 on direct drilled and tilled plots respectively). However, over the year 83 kg N ha−1 were mineralized in tilled plots, and 67 kg N ha−1 in direct‐drilled plots.Five factors governing the leaching of nitrate are assessed and this identified that fertilizer nitrogen application to the seedbed of winter sown crops and the mineralization of nitrogen from the residues of the previous crop are the most significant factors for nitrogen leaching in the UK.
Effects of time and temperature on the bioavailability of Cd and Pb from sludge‐amended soils
Authors: HOODA P. S. , ALLOWAY B. J. 
Published: July 2006

SUMMARYA pot experiment was conducted to compare the behaviour and bioavailability of Cd and Pb from two soils mixed with sewage sludge at three rates (0, 50 and 150 t ha−1) and maintained at two contrasting ambient temperatures (15°C and 25°C) over a period of one year following the treatments. Ryegrass (Lolium perenne) accumulated Cd and Pb in the sewage sludge treated soils, although accumulation was significantly lower in the soils treated at the high rate (150 t ha−1) compared to the low rate (50 t ha−1). Ryegrass grown in the warm environment (25°C) accumulated significantly higher levels of Cd and Pb than that grown in cooler conditions (15°C). Samples of the soils spiked with nitrate salts of Cd and Pb at equivalent rates of metal loading resulted in the ryegrass accumulating much higher levels of both the metals than on the sludge treated soils.Metal uptake by the ryegrass from the sludge treatments increased over successive harvests while that from metal salt treatments decreased. The observed trend of increasing plant metal uptake over time coincided with a trend of decreasing pH in the sludge treatments. However, the concentrations of Cd and Pb extracted by DTPA failed to predict the changes in plant metal uptake. The importance of sewage sludge as both a source and a sink of pollutant metals and the trend of increasing bioavailability over time shown by this experiment are discussed.
The variation of critical‐state parameters with water content for two agricultural soils
Authors: PETERSEN C. T. 
Published: July 2006

SUMMARYTriaxial tests were conducted on 436 reconstituted samples of two agricultural soils (a sandy loam and a loam) at moisture contents from air dryness to close to the respective liquid limits.Volume‐change behaviour was largely consistent with the critical‐state concept, the role of soil‐moisture content being expressed in the values of the measured critical‐state parameters. The most important parameters, and their inherent variability, have been specified. Most of the parameters varied systematically with soil‐moisture content, but differently for the two soils. Some of the parameters were linearly correlated. The specific volume (v) was a linear function of the logarithm of the mean normal stress (In p) during normal compression and along the critical‐state line (CSL) with significantly different gradients (λ and λ*, respectively) at most moisture contents except close to the liquid limits. The standard errors of λ* were typically of the same magnitude as the gradients found during hydrostatic unloading from two different v‐levels whereas the standard errors of λ were up to a factor of ten smaller. The linear projections of the CSLs on the deviatoric stress (q)–mean normal stress plane showed intercepts on the q‐axis. Generally, precompaction leading to brittle failure had very little influence on the shear strength as compared with the strength in critical state.
Net mineralization, net nitrification and potentially available nitrogen in the subsoil beneath a cultivated crop and a permanent pasture
Authors: WEIER K. L. , MAcRAE I. C. 
Published: July 2006

SUMMARYThe brigalow clay soils of central Queensland in eastern Australia contain large quantities of nitrate‐N in the subsoil beneath shallow rooting cultivated crops. A laboratory incubation study was conducted to determine whether nitrate accumulation at depth beneath these crops was due to in situ nitrogen mineralization.Intact soil cores, 5 cm long and 5 cm diameter, were obtained at four depths to 120 cm beneath cultivated black gram (Vigna mungo) and green panic (Panicum maximum var trichoglume) permanent pasture and incubated for 12 weeks at 60% water‐filled pore space and 25°C.Net mineralization of organic N occurred in all soil cores obtained from under black gram with values ranging from 4.3 to 9 mg N kg−1 soil at 12 weeks. Beneath the pasture, net mineralization had not commenced by the end of 12 weeks.Potentially available nitrogen (Na) ranged from 1.2 to 62.7 kg N ha−1 under black gram, and from 10.2 to 136.9 kg N ha−1 under pasture. A significant relationship was observed between Na and total N beneath both crops, and between Na and total C under the pasture.Leaching of N mineralized in the surface layers of soil appears to be the main avenue of nitrate build‐up in the subsoil beneath black gram, with subsoil mineralization making only a partial contribution to the accumulated nitrate pool.