bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of temperature and flooding duration on phosphate sorption in an acid sulphate soil from Vietnam
Authors: VO QUANG DINH , DUFEY J.E. 
Published: August 2005

SummaryPhosphate sorption in soil is controlled largely by Fe‐oxihydroxides, and so important changes in P dynamics are expected when the redox potential is modified. Such changes in P sorption when acid soil is flooded, as for rice cultivation, have been evaluated. Samples from an acid sulphate soil in the Mekong Delta of Vietnam were flooded for up to 56 d at 20°C and 30°C. Some of the samples incubated at 30°C were dried in open air for 30 d after flooding. Small redox potential (Eh<0) and pH>6 were rapidly reached in soil flooded at 30°C; less drastic reducing conditions (Eh ≅0.2 V) and pH 4–5 occurred at 20°C. Phosphate sorption increased during flooding. The increase was twofold at 20°C, and 10‐fold at 30°C. Phosphate sorption index decreased in the soil that was air dried after flooding at 30°C, but still remained two to three times greater than before flooding. These results were compared to the changes in oxalate‐extractable Fe, i.e. poorly crystalline or amorphous Fe‐oxihydroxides. The increase of P sorption per unit increase of oxalate‐Fe was seven to eight fold larger at 30°C than at 20°C.
Dispersion and zeta potential of pure clays as related to net particle charge under varying pH, electrolyte concentration and cation type
Authors: CHOROM M. , RENGASAMY P. 
Published: August 2005

SummaryThe effect of changing pH and electrolyte concentration on the dispersion and zeta potential of Na‐and Ca‐forms of kaolinite, illite and smectite was investigated in relation to changes in their net negative charge.The percentage of dispersible Na‐clay and the percentage increase in net negative charge was positively correlated with pH, but the slopes varied from clay to clay. In general, the net negative charge was the primary factor in clay dispersion, and the pH affected clay dispersion by changing the net charge on clay particles. Na‐smectite had larger net charge at all pHs than Na‐illite and Na‐kaolinite, and it always had larger flocculation values. The role of electrolyte concentration could be due to its effect both on flocculation and variable charge component of the clay minerals. The zeta potential at different pHs also reflected the same trend of clay dispersion with net particle charge.In Ca‐clays the trends were similar to Na‐clays up to pH 7.0. In more alkaline solution CaCO3 formation led to charge reduction on clay particles, resulting in flocculation and reduction of zeta potential. At similar pHs the electrophoretic mobilities of all the clays showed constant potential behaviour. However, the zeta potentials of Ca‐clays were always smaller than those of sodic clays because the clays were more aggregated. Net particle charge was the most important factor in controlling clay dispersion for the whole range of pH and ionic strength and for all types of cations.
Estimating temporal change in soil monitoring: II. Sampling from simulated fields
Authors: PAPRITZ A. , WEBSTER R. 
Published: August 2005

SummaryDesign‐based and model‐based methods of estimating temporal change of soil properties over a finite area have been compared. Two large fields of auto‐ and cross‐correlated data were simulated, each representing the spatial distribution of a variable at one time. The fields were then sampled repeatedly. The means of stratified and systematic random samples and geostatistical global estimates were used to infer the mean difference between the fields. All estimators were unbiased, but their variances differed. Pairing the positions on the two occasions increased the precision of the design–based estimates. Systematic sampling was slightly more precise than stratified sampling. Kriging was less precise than both because some of the sample information must be used to estimate the variograms at short lags. Neither balanced differences nor the normal formula for simple random sampling predicted the estimation variances of small (n< 50) systematic samples accurately. For larger samples the method of balanced differences performed well. If the spatial variation is unknown in advance and only small samples can be taken then stratified random sampling with two observations per stratum is the preferred design. It resulted in the best combination of precision and accuracy in predicting the sampling error.
Land‐use effects on the composition of organic matter in particle‐size separates of soils: II. CPMAS and solution13C NMR analysis
Authors: GUGGENBERGER G. , ZECH W. , HAUMAIER L. , CHRISTENSEN B.T. 
Published: August 2005

SummarySoils from A horizons of Eutrochrepts under spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp), and arable rotation (Ar) were fractionated into clay‐ (<2 μm), silt‐(2–20 μm) and sand‐ (20–2000 μm) sized separates.13C NMR spectroscopy was used to compare SOM composition across size separates and between land‐use regimes.CPMAS13C NMR spectroscopy showed that the intensity of signals assigned to carbohydrates (representing most O‐alkyl C) and lignin (phenolic and methoxyl C) declined with decreasing particle size. Concurrently, alkyl C and C‐substitution of aromatic C increased in the order sand, silt, clay. The amount of alkyl C correlated well with microbial resynthesis of carbohydrates. Solution13C NMR spectra suggested that humic acids (HA) extracted from the size separates were richer in carboxyl C and aromatic C than the bulk size separates. Also HA reflected increasing percentage of alkyl C with decreasing particle size. O‐alkyl C were lower in silt HA than in clay HA whereas aromatic C tended to peak in silt HA. These results suggested that sand‐sized separates were enriched in plant residues (primary resources) whereas clay‐sized separates were dominated by products of microbial resynthesis (secondary resources). Silt was rich in selectively preserved and microbially transformed primary resources.13C NMR spectroscopy showed only small differences in SOM composition between land‐use regimes, except that silt and silt HA from Ar were richer in aromatic C than those from the other plots. But enrichment factors (E= content in fraction/content in whole soil) revealed differences in the distribution of C species across the size separates. Relatively highEaromatic(0.9) andEo‐alkyl(1.0) for sand from Gp indicated high amounts of plant residues, probably due to intense rhizodeposition and to occlusion of plant debris within aggregates. LowEaromatic(0.3) and Eo‐alkyl(0.3) for sand from Ar suggested depletion of primary resources, which could be attributed to disintegration of soil aggregates upon cultivation. A pronounced enrichment of alkyl C in Ar clay‐sized separates (Ealkyl= 3.1) suggested large amounts of microbial carbon. Microbial products attached to clay surfaces by a variety of physico‐chemical bondings appeared more stable against mineralization induced by cultivation than plant residues sequestered in aggregates.
A weathering score for sandy soil materials based on the intensity of etching of quartz grains
Authors: MARCELINO V. , STOOPS G. 
Published: August 2005

SummaryA semi‐quantitative method is developed to assess the relative weathering of tropical sandy soils. Individual quartz sand grains are classified on the frequency and the size of dissolution etch pits in their surfaces, using scanning electron microscopy (SEM). A scale with five grain‐type classes reflecting increasing intensity of etching is defined, and the relative frequency of each of these classes in horizons of selected soil profiles is determined. To summarize the information contained in the frequency distribution a weighted score, the weathering score, is calculated. This score assesses the relative weathering of individual horizons, and it makes it easy to compare them with other horizons within the same or from other profiles. It is useful in detecting weathering trends and differences between horizons of tropical sandy soils.
The dynamics of soil water following single surface wettings
Authors: ROSE D.A. 
Published: August 2005

SummarySingle rainfall events play an important agricultural and ecological role, especially in dry regions where precipitation is erratic. Infiltration, redistribution and evaporation of single quantities of water are important in this context and have been investigated in the laboratory.Three soils of differing texture were packed at two uniform initial water potentials (– 100 MPa and –1.5 MPa) into columns, after which 12.7, 25.4 and 50.8 mm of water were applied as a single irrigation. The columns were maintained in a controlled hot and dry atmosphere (evaporativity = 16.7 mm d‐1) for up to 30 days, during which water‐content profiles were measured at intervals.Infiltration was rapid to depths ranging between 35 and 250 mm. Thereafter redistribution was small. Evaporation caused the water profile to develop three zones: dry between the soil surface and the drying front, dry below the wetting front, and an intermediate wetter zone between the drying and wetting fronts. As evaporation continued, the drying front moved deeper into the soil and the water content in the intermediate zone decreased.During the first few hours evaporation was rapid and constant, at the evaporativity of the atmosphere. Subsequently, evaporation was slower. Total evaporation (E) increased with time (t) as Eα tn for t > 1 d, where n = 0.24 for a loamy sand, 0.33 for a clay loam and 0.31 for a silty clay loam.Weighted‐mean soil‐water diffusivities, averaged over the profile above the wetting front, ranged between 1000–2000 mm2 d−1 at the start of the falling‐rate stage and 200–400 mm2 d−1 near air‐dryness, in reasonable agreement with the few results in the literature.
A simple analytical transfer function approach to modelling the leaching of reactive solutes through field soil
Authors: HENG L.K. , WHITE R.E. 
Published: August 2005

SummaryResults from a previous study, in which two different forms of sulphur fertilizer were applied to a grazed pasture, were re‐examined to show that the movement of sulphate to subsurface drains over three consecutive drainage seasons could be satisfactorily predicted using a simplified analytical form of the transfer function model (TFM). Two simple parametric forms: the exponential Burns and lognormal functions, were used for the probability density function for solute travel, and more realistic assumptions about the biologically mediated source‐sink terms were incorporated. Sensitivity analysis showed that the model's prediction was very sensitive to the retardation coefficient for sulphate relative to the non‐adsorbed solute chloride and the volume of soil water that is effective in solute transport. The procedures can be easily adapted for management purposes.
Changes in the amount and distribution of neutral monosaccharides of savanna soils after plantation of Pinus and Eucalyptus in the Congo
Authors: TROUVE C. , DISNAR J‐R. , MARIOTTI A. , GUILLET B. 
Published: August 2005

SummaryIn the Congo, near Pointe‐Noire, Pinus and Eucalyptus were planted on the savanna for 30 years. We have characterized the effects of this change on land‐use on the composition of carbohydrates in whole soil and particle‐size fractions of the soil. Carbohydrates represent variable proportions of the total soil organic carbon (TOC) of various particle size fractions. The largest proportions of sugar‐C were found in the savanna soil with as much as 250 mg g−1 TOC in the coarsest plant remains and approximately 190 mg g−1 TOC in the finest organo‐mineral fractions, whereas there was always less sugar in plantation soils. The monosaccharide xylose and mannose have different distributions: xylose appears to be the marker of the vegetal inheritance, whereas the dominance of mannose in the clay fraction bears the signature of current microbial sugar synthesis.The quantitative and qualitative evolution of the whole soil carbohydrates was studied as a function of plantation age. Carbohydrate‐C represents 131 mg g−1 of the soil organic carbon in the savanna soil, but decreases to an average value of 75 mg g−1 in plantations more than 6 years old. This appears to be due mainly to the stimulation of the mineralization of the glucose, which represented 60% of the total sugars in savanna soil and only 45–48% in tree plantations. The ratio [arabinose + galactose + fucose]/[rhamnose + xylose], which is the largest in the oldest plantations, is significant for evaluating the replacement of carbohydrates of the original grass savanna by those of the trees.
Land use effects on the composition of organic matter in soil particle size separates. III. Analytical pyrolysis
Authors: SAIZ‐JIMENEZ C. , HERMOSIN B. , GUGGENBERGER G. , ZECH W. 
Published: August 2005

SummarySoil samples from the A horizon of an Eutrochrept under spruce forest and permanent grass were fractionated into clay‐, silt‐ and sand‐size separates. Humic acids extracted from each fraction were analysed by pyrolysis‐gas chromatography‐mass spectrometry. Protection of functional groups by simultaneous pyrolysis and methylation yielded pyrolysates in which methyl esters of fatty acids, aliphatic dicarboxylic acids, abietic acids, phenolic acids and benzenecarboxylic acids were represented. However, methylation was not complete, and unmethylated compounds were also present. Spectra showed differences in humic acid composition between size separates as well as across land use regimes. The abundance of lignin‐derived pyrolysis products increased with decreasing particle size, and was greater in soil under spruce than in soil under grass. Also, the lipid components differed, with hexadecanoic and docosanoic acid methyl esters being the dominant compounds in humic acids from soil under spruce and hexadecanoic and octadecanoic acid methyl esters in the humic acids from grassland. A good correlation was found between previous 13CNMR and wet chemical data and pyrolysis data, indicating that pyrolysis‐methylation can be used for fast detailed chemical characterization of humic acids extracted from size separates.
The chemistry of aluminium in strongly acidified sandy soil in Poland
Authors: POREBSKA G. , MULDER J. 
Published: August 2005

SummaryOrganically‐bound Al in acidic, base‐poor sandy soils seems to be a major contributor to dissolved Al. This hypothesis has been tested under field conditions at two intensely acidified sites. The research was conducted at the agricultural trial fields at Lyczyn, Poland, which have been fertilized continuously for 30 yr with 130 kg ha−1 a−1 N (as NH4NO3 or urea). The effect of depletion of Al on its solubility was also studied.Field data confirmed that mobilized Al originates largely in the organically bound fraction of soil Al. Depletion of this fraction resulted in a considerable decrease in the mobility of Al such that, at pH = 3.0 and reaction times of a few weeks, small amounts of Al were mobilized. Apparently, the rate at which Al is dissolved from structural silicates, which are abundant in the soil investigated, is small. This suggests that at sites in Poland most exposed to acid deposition, where the rates of soil acidification and depletion of organically‐bound Al are greatest, both the concentration of Al and the soil solution pH are expected to decline with time.
Chemical significance of aluminium extracted from three horizons of an acid forest soil, using chloride salt solutions
Authors: PONETTE Q. , ANDRE D. , DUFEY J.E. 
Published: August 2005

SummaryAluminium is usually important in exchange reactions in acid soil, but amounts extracted are strongly affected by procedure. We examined the impact of proton release, following salt addition, on Al removal from three horizons (Oe, Oa and A12) of an acid, brown forest soil.The Al was first extracted with either 1 M KC1, 1mNH4C1 or 0.5mCuCl2on the three horizons limed to pH 5.5. For any lime addition, both the pH drop following salt addition and the amounts of extracted Al were greater with CuCl2than with KC1 or NH4C1. For the Oa and A12horizons there was a single inverse linear relation between amount of Al extracted and the pH of final extract, independent of the extracting cation. In the Oe horizon CuCl2extracted constant amounts of Al, whereas the quantity of Al removed by KC1 or NH4C1 increased linearly as pH declined below pH 3.6.Extra Al was mobilized following unbuffered KC1 extraction, a side effect induced by the extracting procedure itself.Al mobilization increased with increasing H+additions. In the Oe horizon, equilibrium was established rapidly (≤ 24 h), and decreasing the pH of the soil‐KCl suspensions to 2.0 resulted in extracted Al amounts equal to or slightly greater than those obtained with CuCl2solutions. Al amounts extracted with acidified KC1 solutions from the A12were close to those obtained using CuCl2solutions at similar pH in the extract. In the samples from the A12layer, increasing the equilibration time resulted in increasing proton consumption and equivalent release of Al ions in the extract.
Phosphorus sorption in soils of the Mekong Delta (Vietnam) as described by the binary Langmuir equation
Authors: QUANG VO DINH , THAI VU CAO , LINH TRAN THI TUONG , DUFEY J.E. 
Published: August 2005

SummaryPhosphate adsorption isotherms were determined for 20, mostly very acidic, soils from the Mekong Delta. The experimental data were well described by a binary Langmuir equation which considers two groups of sorption sites that differ in their P bonding energies. The maximum P‐sorption capacities of these sites were related to the soil properties by simple linear correlation and by stepwise multiple regression. Results suggest that high energy sites are on Al‐oxihydroxides or small Al‐substituted Fe‐oxides and, to a lesser extent, on poorly ordered Fe‐oxihydroxides. On the other hand, the P‐sorption capacity of low energy sites is mainly related to clay content, and it increases as pH decreases. These sites are also positively correlated with organic carbon and poorly crystalline Fe‐oxihydroxides. However, as these two variables are closely correlated with each other, organic matter is likely to be considered as an indirect factor of P fixation through its association with Fe‐oxihydroxides and not as an important source of P‐sorption sites.The maximum sorption capacity, i.e. the sum of sorption capacities of the two groups of sites, is well described (r2= 0.88) by an equation that takes into account the four variables identified above: Al‐bearing oxihydroxides, poorly ordered Fe‐oxihydroxides, clay content and pH. Grouping the soils according to the orders of Soil Taxonomy, the P‐sorption capacity increases in the following sequence: ultisols < entisols < inceptisols.A P concentration often considered adequate for plant nutrition is 0.2 mg P 1−1solution, and only the high energy sites are involved in sorption at that concentration. Thus an equation including only Al‐ and Fe‐oxihydroxides could be used to fix P norms in these soils.
Phosphate speciation in excessively fertilized soil: a 31P and 27Al MAS NMR spectroscopy study
Authors: LOOKMAN R. , GEERTS H. , GROBET P. , MERCKX R. , VLASSAK K. 
Published: August 2005

SummaryBoth P and Al MAS NMR spectra of samples of excessively fertilized sandy soil provided information about the P and Al speciation. Peak deconvolution was used to interpret reliably and quantitatively the 31P NMR spectra recorded. Most of the P was found to be associated with Al. Part of the P exhibited a chemical shift that could be attributed to octocalcium phosphate, amorphous calcium phosphate or apatite. Apatite has, however, never been reported to occur in sandy soils of temperate climates. A dithionite extraction used to remove interfering Fe from the samples also removed most of the octahedral Al‐P phase. After oxalate extraction more than 99% of the original P signal disappeared. About 7.5 to 11 % of the total oxalate extractable P of the excessively fertilized soil was present as a Ca‐P phase, even though these soils are slightly acid to acid. The estimated size of the Ca‐P phase roughly corresponds to the size of the labile P pool of these soils, as assessed in long‐term batch desorption experiments. It still remains unclear whether the labile P pool should be attributed solely to such a Ca‐P phase.
The effects of time of incubation on the relation between charge and pH of soil
Authors: MORA M.L. , BARROW N.J. 
Published: August 2005

SummarySamples of two Andisols and two Ultisols from southern Chile were incubated with acid or with lime for up to 60 d at 25°C or for 1 day at 40°C or at 60°C. The changes in positive and negative charge were measured. The Andisols reacted slowly at 25°C. They lost protons to the solution at high pH, thus increasing the negative charge on the soils and decreasing the pH of the solution. They gained protons at low pH, thus increasing the positive charge on the soils and increasing the pH of the solution. The Ultisols reacted more quickly but again charge and pH changed through time. For all samples, the rate of reaction was increased by incubating at 60°C. Brief incubation at 60°C produces a similar relation to that obtained after longer incubation at 25°C. This provides a convenient means by which measurements can be made more quickly.
The nature of smectites and associated interstratified minerals in soils of the Gharb plain of Morocco
Authors: BOUABID R. , BADRAOUI M. , BLOOM P.R. , DANIANE M. 
Published: August 2005

SummaryThe mineralogies of ‘Tirs’ (Typic Pelloxererts), and ‘Debs’ (Typic Haploxerolls and Typic Xerochrepts) soils of the Gharb plain in north‐western Morocco are investigated, with special attention given to the determination of the nature of the smectitic phase using the lithium test (Li test) and the alkylammonium method. The sand and silt mineralogy of Tirs soils is dominated by quartz with small amounts of feldspars and kaolinite. The sand and silt fractions of Dehs soils also contain significant amounts of mica, chlorite, and interstratified phyllosilicates. The clay minerals of Tirs soils are predominantly a high‐charge smectite. The estimated interlayer charge for this phase is 0.61 mol(c)/O10(OH)2 and the fraction of tetrahedral charge varies from 38 to 44%. Although the percentage tetrahedral charge is less than 50%, the smectitic phase behaves as beidellite with the Li test. Dehs clays are more heterogeneous, consisting of smectite, vermiculite, illite, kaolinite, chlorite, and interstratified illite/smectite and illite/vermiculite. The Li test and the alkylammonium method demonstrate that a high‐charge smectite or vermiculite is interstratified with illite. A low‐charge montmorillonite is also present both in Tirs and in Dehs soils. The high‐charge beidellitic phase is believed to be a transformation product of mica, whilst the low charge montmorillonite is thought to be inherited from the parent material.