bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metal binding with root exudates of low molecular weight
Authors: MENCH M. , MOREL J. L. , GUCKERT A. , GUILLET B. 
Published: July 2006

SUMMARYRoot exudates were collected from maize plants (Zea mays L.), grown under sterile and hydroponic conditions. Exudates of low molecular weight were isolated by filtration and dialysis (MW 1000) of the nutrient solution and analysed. Metal binding properties of the exudates were investigated at 25°C in 0.1 m NaCIO4 ionic medium, using a potentiometric method. The total acidity of the exudates and the successive stability constants of complexes formed with Cu2+, Pb2+ and Zn2+ were determined.Sugars and organic acids were the major components of the exudates. Measured total acidity was resolved into strong (5.85meq g−1C), weak (2.10meq g−1C) and very weak (2.20 meq g−1 C) acidities. Mono‐complexes were formed with Cu, Pb and Zn and bis‐complexes with Cu. At pH 5, stability constants followed the order Cu>Pb>Zn.
Metal‐humus complexes in A horizons of Thai and Korean red and yellow soils
Authors: VIRAKORNPHANICH P. , WADA S.‐I. , WADA K. 
Published: July 2006

SUMMARYCarbon, Al and Fe (Cpyr, Alpyr and Fepyr) were extracted with 0.1 m Na4P2O7 from 26 A horizon samples of tropical Thai and temperate Korean soils (Ultisols, Alfisols, Oxisols and Inceptisols). The soils, except for one Thai Inceptisol, had similar total C (0.35–3.29%) and Cpyr/total C ratios (0.20–0.41). There were approximately linear relationships between total C or Cpyr and clay content; two groups of soils gave different linear relationships. A curvilinear relationship between Cpyr and (Al + Fe)pyr (milli‐atom kg−1) that can be approximated by an equation: Cpyr= 53 (Alpyr+ Fepyr)1/2– 24 was also found for most Thai and Korean soils. The above relationships indicated that total C and Cpyr would be close to zero at zero clay or zero (Al + Fe)pyr. It was inferred that clay‐humus interaction has a primary importance in the determination of humus content in red and yellow soils in tropical and temperate regions and that the main role of clay is to supply Al and Fe that complex and stabilize humus against microbial degradation.
The formation and characteristics of splash following raindrop impact on soil
Authors: GHADIR H. , PAYNE D. 
Published: July 2006

SUMMARYSplash droplet characteristics were studied using cine‐photography and a simple droplet collection method. Two sizes of falling drop, two heights of fall and a number of target materials including soil, sand, water and rotating sandpaper were used. For a 6 mm drop falling at near terminal velocity about 5000 splash droplets were collected ranging in size from 10 um to more than 3 mm in diameter. The amount of soil material carried by splash droplets was much less in the presence of surface water and increased with the size of water stable aggregates. The energy and momentum balance showed a higher proportion of impact energy and momentum in the resulting splash droplets as the impact energy increased. This suggests that kinetic energy is not a reliable indicator of the erosivity of rain drops.
Aggregation in soils with small amounts of swelling clays. I. Aggregate stability
Authors: BARTOLI F. , PHILIPPY R. , BURTIN G. 
Published: July 2006

SUMMARYThe respective role of organic materials and poorly‐ordered Al and Fe hydrous oxides on soil aggregate stability was studied in silty soils with little swelling clay, using both multivariate analysis and physico‐chemical approaches. Soil disaggregation is a function of the hydrophobic character of organic matter (OM), which depends on the nature of the organic materials, cationic environment and the aggregating effect of Al and Fe hydrous oxides.Two kinds of aggregates >50 μm can be distinguished in organic soils, one being about six times more stable than the other. In soils poor in organic matter, weak aggregates dominate; the binding agents are Ca or Al OM rich in polysaccharides and peptides.
Testing a mechanistic model. VII. The effects of pH and of electrolyte on the reaction of selenite and selenate with a soil
Authors: BARROW N. J. , WHELAN B. R. 
Published: July 2006

SUMMARYThe pH of samples of a soil was altered by mixing them either with acid or lime, and incubating the moistened samples at 60°C for a day. The sorption of selenate and of selenite was then measured using as background electrolytes, 0.01 M, 0.1 M and 1.0 M sodium chloride and also 0.01 M calcium chloride. The results were compared with previous studies with phosphate and fluoride.Selenite was sorbed more strongly than selenate, but not as strongly as phosphate or fluoride. Sorption of both selenite and selenate decreased with increasing pH. This decrease was more marked for selenate than for selenite; more marked in a sodium system than in a calcium one; and more marked with a dilute background electrolyte than a concentrated one. Under certain conditions, the steeper curves for the dilute electrolyte crossed the curves for the concentrated electrolyte giving points of zero salt effect. For selenite, these points of zero salt effect occurred near pH 6 and the greater the sorption the lower the pH for zero salt effect. For phosphate, the analogous value was near pH 5. For selenate, if a point of zero salt effect occurred, it was at such a high pH and such a low amount of sorption that it could not be measured. Thus, the larger the amount of sorption the lower the pH for the point of zero salt effect. This generalization applied both within and between different kinds of sorbates.The results were closely described by a model that had previously been applied to phosphate and fluoride. The model postulates that ions react with charged surfaces. The electric potentials of the reacting surfaces are affected by the identity and concentration of the background electrolyte and this produces the interactions between pH and electrolyte concentration. The model also postulates that there is a distribution of electric potentials. Anions react with surfaces which occur in the more positive tail of this distribution. The smaller the amount of the reaction the more positive the potential of the reacted surface and, therefore, the higher the pH required to decrease this potential to zero.
The effects of lime on adsorption and desorption of phosphate in five Colombian soils
Authors: LE MARE P. H. , LEON L. A. 
Published: July 2006

SUMMARYThe effects of lime (applied in the field) on the amounts of total and isotopically‐exchange‐able phosphate adsorbed from solutions were measured in five soils. The total amount of phosphate adsorbed without lime was in the range 200 to 1700 μg P per g of soil at 0.05 μg P cm−3 of solution. Lime diminished the amount of phosphate adsorbed at all concentrations of solution in an oxisol and a dystropept; in an ultisol and another dystropept, lime tended to increase sorption at small concentrations and diminish it at large concentrations; in a dystrandept that contained spheroidal allophane and a great deal of organic matter, lime increased adsorption at all concentrations up to 1 μg P cm−3. Lime increased the proportion of added phosphate that was isotopically exchangeable in the oxisol and one dystropept, had no effect in the other dystropept, and diminished the proportion in the ultisol and dystrandept.Adsorbed phosphate was subsequently desorbed by suspending the soils in solutions without phosphate. After desorption the quantity of exchangeable phosphate in all soils was closely correlated with aluminium extracted by ammonium oxalate; buffer power was correlated in all except the dystrandept, in which it was larger per unit of aluminium than in the other soils; possibly the cause was aluminium associated with organic matter. In all soils lime diminished buffer power allowing a specific amount of exchangeable phosphate to maintain a larger concentration in solution. The beneficial effects of lime on exchangeable phosphate after desorption were consistent among soils, despite inconsistent results when the phosphate was adsorbed.
Acid rain, cation dissolution, and sulphate retention in three tropical soils
Authors: PATIL S. G. , SARMA V. A. K. , VanLOON G. W. 
Published: July 2006

SUMMARYSurface and subsurface samples of three tropical soils were examined with respect to their interaction with dilute solutions of sulphuric acid of pH 3. In calcareous clayey samples with a large cation exchange capacity the H+ was replaced by an equivalent concentration of metal cations which remained in solution along with SO2‐4 as counterion. In a coarse‐textured neutral soil with small cation exchange capacity, there was less chemical interaction and a major proportion of the H2SO4 remained unchanged in the equilibrium solution. Another soil exhibited considerable ability to remove SO2‐4 from solution and, therefore, the total ionic concentration was greatly reduced. Other samples showed behaviour which was intermediate to these three types.The ability to adsorb SO2‐4 is one of the most important factors which determines the nature of the interaction of soil with dilute sulphuric acid. This ability was shown to be affected by the content of hydrous sesquioxides and organic matter in these soils.
Carbohydrate composition of hay and maize soils and their possible importance in soil structure
Authors: BENZING‐PURDIE L. M. , NIKIFORUK J. H. 
Published: July 2006

SUMMARYThe soils of three fields under continuous maize culture for 2,4 and 15 yr, and the soil of an adjacent hayfield were analyzed for carbohydrates by gas chromatography. A sharp decrease (30%) in total carbohydrates, paralleled by a smaller decrease in organic matter (9%), was observed after 2 yr of maize cultivation. The 4‐yr maize soil showed an upward trend in both organic matter and carbohydrate content but this was subsequently reversed. The 15‐yr highly‐compacted maize soil had 40% less organic matter and 40% less carbohydrates than the hay soil. When compared to the well structured 2‐yr maize soil, this compacted soil had less arabinose, xylose, glucose, galactose and mannose; carbohydrates which are probably of plant root origin. These sugars are likely to be involved in the structural stability of soil aggregates. Conversely, neither the amino sugars nor the uronic acids seemed to contribute to good soil structure.
Steady‐state denitrification in aggregated soils: a mathematical model
Authors: ARAH J. R. M. , SMITH K. A. 
Published: July 2006

SUMMARYA model is presented which calculates steady‐state denitrification rates as a function of more readily‐measured soil parameters: the soil moisture characteristic, the probability distributions of aggregate size and oxygen reduction potential, the nitrate concentration, and the moisture tension. The model does not depend on curve‐fitting. It indicates that aggregates of intermediate size may be more efficient denitrifiers than very large ones. It provides a theoretical explanation for the reported observation of proportionality between denitrification rate and calculated anaerobic fraction of incubated soil cores. This proportionality extends over some five orders of magnitude and appears to be independent of moisture tension. Calculated whole‐soil denitrification rates are affected principally by soil texture, structure and moisture tension, and less so by nitrate concentration. In addition to predicting denitrification rates, the model may be extended to predict the fraction of the gaseous products of denitrification emitted as nitrous oxide.
Genesis of a Xeralf on feldspathic sandstone, South Australia
Authors: CHITTLEBOROUGH D. J. 
Published: July 2006

SUMMARYA Xeralf on feldspathic sandstone was sampled from a hillslope in the Mount Lofty Ranges in order to study its genesis and, in particular, the origin of the strong texture contrast. Micromorphological study demonstrated that the clay present in void argillans and papules in the B2 horizon accounted for only a small amount of the clay present. Elemental analysis of the whole soil (< 2 mm) and sand, silt and clay fractions showed that there had been considerable weathering of both quartz and microcline, which were the dominant minerals present. Kaolinite is the dominant clay mineral weathering product. Illite appears to be forming from vermiculite in the A horizon. Using zircon as an internal standard, it was shown that elemental losses of SiO2 and reductions in weight and volume were similar in A and B horizons. Losses of aluminium and potassium were greatest in the A horizon, least in the B3. There has been an absolute increase in the amount of iron. A possible source is iron from heavy mineral bands upslope. It was concluded from the similarity of the quartz particle‐size distributions of the A2, B2 and B3 horizons that the intensity of weathering of quartz was the same in A and B horizons. In the case of feldspar (mostly microcline), there is a greater proportion of feldspar in the fine sand and silt fractions of the A2 horizon than in the B horizon. Weathering of feldspar is greatest in the A horizon. The texture profile is principally a function of greater lateral loss of clay from the A horizons compared to the B horizons.
Effect of rewetting air‐dried soils on pH and accumulation of mineral nitrogen
Authors: HAYNES R. J. , SWIFT R. S. 
Published: July 2006

SUMMARYThe effect of rewetting a number of air‐dried soils on pH and on accumulation of mineral‐N was examined in a laboratory incubation study. When rewetted‐soils were incubated at 25°C three patterns of change in soil pH and in accumulation of mineral‐N were observed. Ammonification and nitrification proceeded together in soils with pH values greater than 6.0; soil pH decreased whilst concentrations of nitrate rose and those of ammonium remained low. By contrast, in soils with pH values less than 5.0, although ammonification proceeded there was no appreciable nitrification; soil pH increased whilst concentrations of ammonium rose and those of nitrate remained very low. In a third group of soils with pH values between 5.0 and 5.5, there was a delay in nitrification, but ammonification was not retarded; soil pH initially rose as concentrations of ammonium increased, but when nitrification subsequently commenced the pH decreased, concentrations of nitrate rose and those of ammonium declined. When microbial activity in rewetted soils was inhibited by incubation at 3°C, or in a chloroform atmosphere at 25°C, there was little change in concentrations of ammonium and nitrate, and soil pH remained relatively constant.Such changes in soil pH, induced by ammonification and nitrification, are likely to have important consequences to soil chemical studies where pH‐dependent reactions are being studied using rewetted soils. Changes in pH can be minimized by using field moist rather than air‐dried soils.
Loss of availability of phosphate in New Zealand soils
Authors: PARFITT R. L. , HUME L. J. , SPARLING G. P. 
Published: July 2006

SUMMARYPhosphate sorption was measured by the method of Barrow (1980) using a laboratory incubation procedure for up to 60 d on four soils which had different mineralogies but medium to high phosphate retention. All the soils had slow reactions where phosphate sorption continued, but at a decreasing rate, with time. The rate of decrease in the slow reactions was similar on all the soils. Phosphate became less available to plants during the slow reactions, and results of a pot trial with white clover showed that, on all the soils, phosphate incubated with the soils for 218 d was about 65% as effective as phosphate incubated for 10d.When 700 mg P kg−1 was added to allophanic soils (Andisols), about 100 mg kg−1 was strongly adsorbed, about 200 mg kg−1 became unavailable in about 200 days and the remainder was weakly adsorbed. A similar result was obtained on Waiarikiki soil (Inceptisol), which contained ferrihydrite and Al‐humus as the predominant reactive species. On the Kerikeri soil (Oxisol) about 150 mg P kg−1 became unavailable with time as a result of reactions with geothite, hematite and Al‐humus.The phosphate uptake by the microbial biomass was similar to the uptake by the clover, and immobilization of phosphate in the biomass can contribute to the loss of availability of phosphate in soils.
Effects of long‐term phosphatic fertilizer applications on amounts and forms of phosphorus in soils under irrigated pasture in New Zealand
Authors: CONDRON L. M. , GOH K. M. 
Published: July 2006

SUMMARYIn this study a detailed sequential fractionation scheme was used to examine the effects of long‐term annual applications of phosphatic fertilizer on the amounts and forms of phosphorus (P) in soils under intensively grazed irrigated pasture over a 25 year period (1952–1977). Results showed that increases in soil inorganic and organic P occurred in response to continued P fertilizer addition, although inorganic P decreased with time following the cessation of P fertilizer inputs in the residual fertilizer and control treatments. The rate of organic P accumulation in soils decreased with time, while a marked decline in soil organic P in all treatments between 1971 and 1974 was attributed to increased mineralization as a result of lime addition in 1972. Furthermore, changes in the forms of inorganic P which accumulated in the continually fertilized soils after 1971 were attributed to the combined effects of liming and changes in the chemical nature of applied fertilizer P.
Effect of microorganisms on extractability of Cd from soil with NaOH and DTPA
Authors: BOLLAG J.‐M. , CZABAN J. 
Published: July 2006

SUMMARYBecause Cd is extremely toxic, an understanding of the factors that allow or prevent Cd entrance into the food chain is important. The fate of Cd in soil is strongly influenced by microbial activity. Thus, an attempt was made to develop a method for studying the effect of microorganisms on Cd sorption to soil and availability to plants. It was found that the amount of Cd extracted from soil to soil suspensions with 0.1 m NaOH is related to microbial proliferation. In addition, an increase of Cd in NaOH extracts occurred concurrently with a decrease of Cd in DTPA extracts. Our observations suggest that the binding of Cd to microorganisms or their products can immobilize Cd and consequently affect its bioavailability.
Characterization and stability of transition metal complexes of chestnut (Castanea sativa L.) leaf litter
Authors: SENESI N. , SPOSITO G. 
Published: July 2006

SUMMARYThe water‐ and acid‐insoluble fractions of a chestnut (Castanea sativa L.) leaf litter sample and their complexes with Cu(II), Fe(III), and Mn(II) prepared in the laboratory were characterized by major elemental analysis, total Cu, Fe, and Mn content, infrared (IR), and electron spin resonance (ESR) spectroscopy. The IR spectra revealed a broad typology of functional groups (particularly carboxyls) in the solid litter, whereas the ESR spectra showed the existence of indigenous organic free radical species, inner‐sphere Fe3+ complexes, and outer‐sphere Mn2+ complexes. The litter exhibited a high residual binding capacity for Cu, Fe, and Mn in chemical forms of differing stability against water leaching and proton exchange. The ESR spectra of the metal complexes prepared in the laboratory indicated that Fe3+ and Cu2+ formed highly water‐stable, inner‐sphere complexes, whereas Mn2+ formed water‐labile, outer‐sphere complexes. Oxygen ligands of the litter were involved in metal complexation in all cases. The litter showed the highest affinity for Cu2+, followed by Fe3+ and Mn2+, when it was reacted with a single metal, whereas it complexed Fe3+ preferentially in the presence of both Cu2+ and Fe3+. Only a limited portion of the metal ions retained at the pH of distilled water remained bound in stable forms by the litter when the pH was lowered. Thus, variations of pH in forest soils will significantly affect micronutrient metal content and mobility in leaf litter.
Optimal interpolation and isarithmic mapping of soil properties. VI. Disjunctive kriging and mapping the conditional porbability
Authors: WEBSTER R. , OLIVER M. A. 
Published: July 2006

SUMMARYDisjunctive kriging is a technique for estimating values of spatially distributed random variables by combining data non‐linearly and with minimum variance. Data are transformed using Hermite polynomials to a normal distribution, and the resultant transformation is assumed to produce a stationary bivariate normal distribution for all pairs of data. Conditional probabilities that the true values exceed or are less than a specified critical threshold can then be calculated. For soil survey both the estimated values of soil properties and their associated probabilities can be mapped isarithmically as aids to decisions on land management.The technique is described and illustrated from two case studies. The pH, exchangeable potassium and available phosphorus are mapped over 77 ha of the Broom's Barn Farm, and in the eastern Border Region of Scotland the available copper and cobalt in the topsoil are mapped. The estimates are similar to those obtained by simple (linear) kriging. The conditional probabilities were estimated for values falling short of the minimum recommended thresholds, and maps of them showed where farmers would be advised to remedy or forestall deficiencies in lime and plant nutrients and to take prophylactic measures for their livestock.
A simple predictive approach to solute transport in layered soils
Authors: DYSON J. S. , WHITE R. E. 
Published: July 2006

SUMMARYSolute transport through layered columns (repacked aggregates overlying sand) was studied under steady flow conditions. Predictions of transport were simplified by assuming that the distribution of solute travel times in one layer was not correlated with that in the other. The implications of this assumption were developed for the transfer function model (TFM) and the convection‐dispersion model (CDM) of solute transport. The parameter values in each model were obtained from experiments carried out on columns containing only aggregates or sand.The solutes used were nitrate (surface‐applied) and chloride (previously distributed); predictions of the chloride movement were made using the parameter values for the nitrate. The predictions were tested against experimental values of drainage effluent concentration and solute concentration with depths in the columns (measured at the end of the experiments). The TFM (with an assumed lognormal distribution of travel times) and the CDM did not differ significantly, mainly because the spatial scale of the experiments was small.Because the parameter values for the columns of aggregates or sand were determined from the drainage effluent data, they were average values for whole columns. These parameters were satisfactory for predicting drainage effluent concentration from the two‐layer columns. However, they were not satisfactory for predicting the depth distribution of solute, particularly in the sand, because the water content of the sand increased with depth, unlike that of the aggregates, which was approximately constant with depth. The overall results of this study on materials of differing transport characteristics suggest that the assumption of uncorrelated travel times between layers has a potentially wide application. The approach taken here needs to be tested on undisturbed layered soils.