bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phosphorus forms in a sandy soil (Torripsamment) under palm orchards of different age in Saudi Arabia
Authors: HEAKAL M.S. , AL‐AWAJY M.H. , AL‐SEWAILEM M.S. , BARAKAH F.N. , AL‐ASHEIKH A. 
Published: August 2005

SummaryFlood irrigated date‐palm orchards annually manured for 10 (=U10), 50 (=U50, 110 (=U110) and 230 (U230) years together with a barren site in a nearby desert (=U0) all on sandy soils, were analysed for total P (TP), organic P (OP), inorganic P extracted by 0.5mH2SO4(Ca‐P), inorganic P not extracted by 0.5mH2SO4(NP), total N (TN) and organic C (TC). Watering resulted in continuing CaCO3accumulation in the soils. TC and TN to 160 cm depth increased rapidly over the first 50 years (120 g C m−2a−1and 9.7 g N m−2a−1), then the increases slowed. In contrast, TP continued to accumulate steadily (4.8 g P m−2a−1). AtU0, TP to 160 cm depth was very small (= 88 mg kg−1) and dominated by Ca‐P with OP as a minor component. AtU10, OP and Ca‐P were in equal proportions. The latter acquired increasing dominance with increasing period of treatment whereas OP reached a steady state. NP increased at a rate which decreased with time. It is likely that most of OP compounds have been leached down the profile where mineralization and subsequent immobilization, probably by Ca2+ions from irrigation waters, have occurred.
Evidence for microbial decomposition of organic acids during podzolization
Authors: LUNDSTRÖM U.S. , VAN BREEMEN N. , JONGMANS A.G. 
Published: August 2005

SummaryMicrobial aspects of podzolization were studied by percolating organic acids through sterile and non‐sterile soil in columns. Six columns containing sand from a fluvioglacial sediment were percolated (90 mm d−1) with mor extract and an oxalate‐citrate solution. In three of these, sterilized soil solutions were used. Weathering was enhanced by organic acids which formed complexes with aluminium and iron. In the non‐sterile soil columns weathering by organic acids was inhibited at 7–8 cm because the acids were degraded by microorganisms. Weathering was evident from colour change, contents of extractable aluminium and iron, and the micromorphology. Enhanced weathering in the sterile columns was also suggested by larger amounts of aluminium, iron, silica and base cations leached from the columns. Comparison of the output of aluminium, iron and silica from the sterile soil with that from the non‐sterile soil, suggests that probably an aluminium‐iron‐silicate phase was formed in the deeper parts of the non‐sterile columns.
Nitrous oxide fluxes from grassland in the Netherlands: I. Statistical analysis of flux‐chamber measurements
Authors: VELTHOF G.L. , OENEMA O. 
Published: August 2005

SummaryAccurate estimates of total nitrous oxide (N2O) losses from grasslands derived from flux‐chamber measurements are hampered by the large spatial and temporal variability of N2O fluxes from these sites. In this study, four methods for the calculation of mean N2O fluxes (n= 6) on total N2O losses are compared, namely the arithmetic mean, the geometric mean, the lognormal mean and the mean derived from Finney's method. Mean fluxes were calculated from weekly flux measurements on grassland at four contrasting sites in the Netherlands with three management treatments each. Total losses were calculated by interpolation of the mean fluxes and integration over time. Spatial variation of N2O fluxes was large. The geometric mean was generally much smaller, up to a factor of 7, than the arithmetic mean. The lognormal mean was much larger, up to a factor of 11, than the arithmetic mean, possibly because this estimator is biased for small sample size. Arithmetic means and Finney's method were generally in reasonable agreement. The order in estimated N2O loss increased in the order geometric mean<arithmetic mean≤Finney's mean<lognormal mean. Because of the small sample size (n =6), the uncertainty about the precise frequency distribution, the sensitivity of estimators based on logtransformed data, and the problems associated with negative fluxes, the arithmetic mean was preferred as the most appropriate estimator. Evidently, the choice of an estimator of the mean can have great effects on the estimation of total N2O losses.
Effects of organic and inorganic calcium compounds on soil‐solution pH and aluminium concentration
Authors: SMITH C. J. , GOH K. M. , BOND W. J. , FRENEY J. R. 
Published: August 2005

SummaryThe reactions of two organic (citrate and fulvate) and two inorganic (chloride and phosphogypsum) calcium compounds were studied during leaching of columns of unsaturated acidic soil. The potential of these compounds to decrease the aluminium concentration in the soil solution and remove exchangeable aluminium, and their effects on soil acidity are described.The calcium citrate solution increased the soil solution pH from 5 to a maximum value of 7 in the upper portion of the column. In contrast, the fulvate, calcium chloride and phosphogypsum solutions had little effect on soil‐solution pH. Treatment with calcium citrate, or fulvate solution that contained 51 mm Na, removed most of the exchangeable aluminium from the column. The cation exchange sites in the upper portion of the column were saturated with calcium, and the cation exchange capacity of the soil was increased from 35 to c. 80 mmolc kg−1 in the calcium citrate treatment. Leachate from this treatment contained low (< 2 mm) calcium concentrations and high aluminium concentrations. In contrast, the above changes were not shown by the calcium chloride and phosphogypsum treatments. In these treatments the calcium concentration in the leachate was equal to that in the inflowing solution, which indicated that calcium was transported through the entire column. These results suggest that calcium alone was ineffective in displacing aluminium from the cation exchange sites and a strong complexing agent such as citrate or fulvate is needed to mobilize the exchangeable aluminium.
Theoretical analyses of interactions between inorganic nitrogen and soil organic matter
Authors: BOSATTA E. , ÅGREN G.I. 
Published: August 2005

SummaryThe organic matter of the soil has a large potential to retain inorganic nitrogen by means of both biotic (microbially mediated) and abiotic (chemical) reactions. We derive one equation with which we analyse the nitrogen retention due to these mechanisms in terms of organic matter properties. We first of all show how to separate gross mineralization from immobilization. We then show that our equation can reproduce studies of microbially–mediated or purely inorganic immobilization. We then apply the theory to soils of different characteristics (typical agricultural and forest soils) and find that the major factor determining the fraction of added inorganic nitrogen that is immobilized is the ratio between soil carbon and inorganic nitrogen concentration.
Decomposition of15N‐labelled catch‐crop residues in soil: evaluation of N mineralization and plant‐N uptake potentials under controlled conditions
Authors: NICOLARDOT B. , DENYS D. , LAGACHERIE B. , CHENEBY D. , MARIOTTI M. 
Published: August 2005

SummaryThe decomposition of15N‐labelled catch‐crop materials (rape, radish and rye), obtained from field experiments, was studied in a chalky Champagne soil during a 60‐week incubation at 28°C. Mineralized N was assumed to come from either labile or recalcitrant fractions of plant residues. The labile fraction represented about one‐third of the catch‐crop N; its mineralization rate constant varied from 0.06 to 0.12 d−1. The decomposition rate of the recalcitrant N fraction ranged from 0.03 × 10−2to 0.06 × 10−2d−1. Catch‐crop species and rate of incorporation had no effect on N residue mineralized at the end of incubation.The decomposition of labelled rye was monitored in the same soil during a 5‐month pot experiment to determine the N availability to an Italian ryegrass crop and the effect of plants on the decomposition processes. The15N‐rye decomposed rapidly both in the presence or absence of Italian ryegrass, but the amounts of N mineralized were influenced by the presence of living roots: 42% of the15N in labelled rye was present as inorganic N in the pots without plants after 5 months, compared with only 32% in the ryegrass crop. Comparison of microbial‐biomass dynamics in both treatments suggested that there had been preferential utilization by soil micro‐organisms of materials released from the living roots than the labelled plant residues.
Solubility characteristics of proto‐imogolite sols: how silicic acid can de‐toxify aluminium solutions
Authors: LUMSDON D.G. , FARMER V.C. 
Published: August 2005

SummaryProto‐imogolite sols can be considered as highly dispersed forms of proto‐imogolite allophane, the most widespread type of allophane in volcanic and non‐volcanic soils world‐wide. The solubility characteristics of such sols define the conditions of precipitation of allophanes in soils, and the maximum concentrations of aluminium released during acidic episodes from soils, such as podzols, that contain allophane. Direct measurement of Al, Si and pH values in equilibrium with proto‐imogolite sols, approached from higher and lower pH, indicated a solubility equation:
image

where log*Kso lay in the range 7.14 to 7.23 after equilibration for 4–24 weeks at 22 + 2°C in 17 of the 20 systems studied. The mean value of log *KSO at 298 K was calculated as 7.02. This value indicates that proto‐imogolite will be more stable than amorphous aluminium hydroxides at H4SiO4 concentrations above 5 × 10−6m, but less stable than bayerite below 10−3m H4SiO4, and than gibbsite below 10−2m. Proto‐imogolite is more stable than micro‐crystalline gibbsite in 10−4m H4SiO4, a typical minimum concentration in soil solutions and streams in landscapes where podzols are present. The rapid formation of proto‐imogolite effectively prevents the formation of gibbsite seeds in soil, except in highly leached and warm environments, i.e. in older landscapes in the tropics.Although the presence of 10−4m silicic acid has been found to eliminate the acute toxicity to fish exhibited by solutions containing 6–7 μm Al at pH 4.96, little or no proto‐imogolite would form under these conditions. Silicic acid would, however, prevent the precipitation of aluminium hydroxides, and could inhibit the formation of the A113 polycation. These polymeric species are a likely cause of the increased toxicity exhibited by partially neutralized aluminium solutions.
Partitioning of polycyclic aromatic hydrocarbons (PAH) to water‐soluble soil organic matter
Authors: MAXIN C.R. , KÖGEL‐KNABNER I. 
Published: August 2005

SummaryThe mobility of polycyclic aromatic hydrocarbons (PAH) in soils can be influenced by the presence of dissolved organic matter. Partition coefficients of selected polycyclic aromatic hydrocarbons, ranging from 3‐ring to 6‐ring compounds, to water‐soluble soil organic matter (WSSOM) were determined. Partition coefficients were determined for WSSOM obtained from two soils under agricultural use and forest and for commercially available humic acid (Aldrich), taking advantage of a reversed phase (C18) separation method. The WSSOM was characterised with regard to charge and hydrophilic/hydrophobic properties with a dissolved organic matter (DOM) fractionation method. No sorption to WSSOM was found for the tri‐ and tetracyclic PAH, whereas the penta‐ and hexacyclic PAH showed a significant binding to both types of WSSOM and to Aldrich humic acid. The affinity of penta‐ and hexacyclic PAH to WSSOM was considerably lower compared to the affinity to Aldrich humic acid. This is suggested to be due to the lower amount of hydrophobic fractions, c. 30%, in the natural WSSOM as compared to Aldrich humic acid. Effective partition coefficients (Koceff) for the sorption of PAH to bulk soil calculated from KDOC and DOM in the naturally occurring concentration range were only 60–70% of the Koc values in pure water. The impact of DOM on pollutant transport is further influenced by non‐equilibrium behaviour of PAH in soils and by sorption of DOM to the solid‐soil matrix. Several scenarios are described in which the effect of DOM on pollutant transport may become important.
Structural change induced by wetting and drying in seedbeds of a hardsetting soil with contrasting aggregate size distribution
Authors: BRESSON L.M. , MORAN C.J. 
Published: August 2005

SummaryHardsetting has been related to two main processes: (i) development of strength when the soil is still moist (–100 kPa) due to matric suction acting within interparticle and interaggregate bridges and (ii) temporary cementation of dry soil by poorly ordered silica and aluminosilicates. In both cases, hardsetting of a seedbed should depend on geometric aspects of macro‐ and micro‐structure. This study deals with aggregate breakdown and/or deformation on wetting and with the structural changes which follow on drying. Repacked seedbeds of a hardsetting red‐brown earth were wetted by capillary rise. Seedbeds with a coarse and a fine aggregate size distribution were examined. Before and after wetting, the bulk density of the seedbeds was measured at 5‐mm increments using a gamma probe. Replicate samples were air dried, gamma scanned and impregnated. Binary images of pore space (> 107 μm) of vertical faces were used to generate depth functions of structure attributes, including macroporosity. Bulk density measurements combined with image analysis resulted in successful structure characterization. Thin‐section observations were used to interpret the quantified changes in terms of physical processes. In both coarse and fine seedbeds the physical processes which determined structural change occurred upon wetting rather than on drying. Coalescence of aggregates under plastic conditions, partly due to overburden pressure and enhanced by microcracking and partial slaking, occurred at the bottom of the coarse seedbed. In the fine seedbed, the fine material agglomerated due to matric suction. These different processes led to rather similar, microporous microstructures which exhibited similar strength properties after drying.
Modelling surface roughness by a Boolean approach
Authors: BERTUZZI P. , GARCIA‐SANCHEZ L. , CHADOEUF J. , GUERIF J. , GOULARD M. , MONESTIEZ P. 
Published: August 2005

SummaryA model for simulating surface roughness of an agricultural bare soil is described. The model used a random Boolean function. The primary function was a sphere with radius r lying on a plane. The intensity function, a(r), of the distribution of the sphere radius was described by a(r) =αrβexp(λr)Microtopography data were collected during two sets of field experiments. The distribution of experimental heights was used for fitting the three parameters, (α, β, λ) of the intensity function a(r) with a pseudo‐likelihood method. Comparisons between experimental and simulated soil surfaces indicated that the simulated roughness was not unrealistic. However, they also showed that the model is currently limited by the primary function and the intensity function that were chosen.
Solubilization of phosphate by rice plants growing in reduced soil: prediction of the amount solubilized and the resultant increase in uptake
Authors: KIRK G.J.D. , SALEQUE M.A. 
Published: August 2005

SummaryPrevious work has shown that rice plants growing in reduced soil are able to solubilize P by inducing an acidification in the rhizosphere through H+produced in Fe2+oxidation by root–released O2, and by the direct release of H+from the roots to balance excess intake of cations over anions. In this paper, equations for the diffusion and interaction of P and acid in soil are developed to predict the resultant increase in P uptake by the roots. Good agreement was obtained between the profiles of P and pH in the rhizosphere measured in the previous experiments, and those predicted using the equations with independently measured parameter values. The equations showed that solubilization accounted for over 80% of the P taken up. Measurements of the solubilization parameters in a range of reduced rice soils showed that H+addition increased the quantity of P that could be desorbed per unit weight of soil and the concentration of P in solution, in all the soils tested. The quantity of P solubilized per unit H+added at a given solution P concentration varied about 50–fold between soils, with a median of 11.9 mmol P per mol H+. The native soil solution P concentration varied 50–fold (median = 0.91 UM) and the soil pP buffer power (the quantity of P desorbed per unit decrease in –log of the P concentration in solution) varied 100–fold (median = 0.36 mmol kg−1pP−1); the soil pH buffer power varied 7–fold (median = 0.075 mmol kg−1pH−1). Calculations indicated that, in most of the soils tested, rice plants would depend upon solubilization for the bulk of their P.
The effects of long‐term superphosphate application on soil organic matter content and composition from an intensively managed New Zealand pasture
Authors: MURATA T. , NGUYEN M.L. , GOH K.M. 
Published: August 2005

SummaryChanges in quantity and composition of soil organic matter (SOM) in pasture receiving annual superphosphate (SP) applications for 41 years at 0 (control), 188 and 376 kg SP ha−1a−1were investigated in soil samples collected from 0–75 and 75–150 mm depths by determining total carbon (TC), total nitrogen (TN), biomass C (BC), biomass N (BN) and subjecting the soils to sequential extraction using cold water, hot water, a mixture of hydrochloric (0.1 M HC1) and hydrofluoric (0.3 M HF) acids (HCl/HF), and sodium pyrophosphate (Na4P2O7) followed by sodium hydroxide (NaOH) for extracting labile and stable SOM fractions. There were significant differences in some SOM fractions between control (0) and SP treatments (188 and 376), especially in the topsoil (0–75 mm) but these were not observed between the two SP treatments. Soil TN (0–75 mm), BN and BN: TN ratio (0–75 and 75–150 mm depths) and the proportion of hot–water–extractable C (HC) in soil TC (HC:TC) (0–75 mm) were significantly greater in the SP treatments than in the control. HC1/HF extractable C and the proportions of soil TC as HC1/HF extractable C (HC1/HF extractable C: TC) were smaller in the topsoil of SP treatments than in the control. Similar results were observed in humin N: TN ratio and the proportions of soil TC as cold–water–extractable carbohydrate (CWcC: TC) and of soil HC as hot–water–extractable carbohydrate (HWcC : HC). Increases in the proportion of labile fraction in SOM were reflected in values of BN, BC: BN, BN: TN, HWcC : HC and HC: TC whereas decreases in the proportion of stable fraction in SOM were found in humin N: TN and HCl/HF–extractable C: TC ratios. Increases in labile SOM (BN and N–containing compounds such as amino acids and amino sugars, which were extractable by hot water but were not present as carbohydrate) and decreases in stable SOM (HC1/ HF–extractable C and humin fraction) in soils under pastures treated with annual SP applications compared with the control were attributed to pasture improvement and the amelioration of P and S deficiency, resulting in a greater return of plant residues and animal excreta and also an increase in clover growth and associated biological N2fixation. The additional labile SOM in SP treatments compared with that of the control was not associated with the soil mineral Al and Fe components.
The effect of strong hydroxide solutions on the stability of aggregates and hydraulic conductivity of soil
Authors: LIEFFERING R.E. , McLAY C.D.A. 
Published: August 2005

SummaryThe effect of two hydroxides (NaOH and KOH) and two chlorides (NaCl and KCl) on aggregate stability and saturated hydraulic conductivity (Ks) was studied in three New Zealand soils using concentrations (0.003, 0.03, and 0.3m) typical of the range ofpH found in strongly alkaline industrial liquid wastes. The different solutions were used as pretreatments prior to aggregate stability measurements and as influent solutions forKsmeasurements.The concentration of hydroxide appeared to be the most important factor affecting aggregate stability andKSin all soils. Aggregate stability andKsdecreased with increasing hydroxide concentration, but were generally unaffected by chloride solutions. RelativeKsdecreased to <2.5% of initialkSwith all hydroxide concentrations, but the time until a decrease ocurred depended on concentration. In contrast, relativekSremained > 100% with chloride solutions, but decreased substantially when distilled water replaced the chloride solutions. Differences in aggregate stability andKsdue to the cation present (either Na+or K+) appeared to be very small. A surface crust formed in the upper 1 cm of the soils leached with hydroxide solutions. This surface crust had substantially less organic carbon than the upper 1 cm of soil from the cores leached with chloride.A two‐stage process explains the decrease inkswhen strongly alkaline solutions are applied to soil. First, organic matter dissolution decreases aggregate stability, with the rate of organic matter dissolution depending on hydroxide concentration; and second, increased repulsion of soil particles (due to increasedpH) causes movement of dislodged particles into pore spaces, resulting in decreasedKs.
Factors affecting the sorption and fixation of caesium in acid organic soil
Authors: HIRD A.B. , RIMMER D.L. , LIVENS F.R. 
Published: August 2005

SummaryRadioactive caesium deposited on upland Britain following the Chernobyl accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentration of Cs+ required to cause Cs+ fixation is 0.60 to 0.75 mm, and this is unlikely to be reached in any contaminated upland soil. It is suggested that the fixation is caused by interlayer collapse of the illitic clay. The observed Cs+ fixation in lowland mineral soils and its absence from acidic upland soils is explained by the action of K+ ions, which can also induce interlayer collapse.Although Cs+ ions are unlikely to be fixed in acid organic soils, they can be strongly sorbed on any unoccupied Cs‐specific sorption sites in the narrow parts of illitic wedge zones. A method for determining the number of such sites is described. For two of the soils studied the number of sites ranged between 8 × 10−8 and 1 × 10−5 mmol kg−1; for two others there appeared to be no unoccupied Cs‐specific sites. Although Cs+ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the concentration of Cs+ in solution is decreased. Thus, radioactive Cs in such soils will remain available for plant uptake, unless interlayer collapse can be induced.
Forms and rates of release of 137Cs in two peat soils
Authors: LIVENS F.R. , HOWE M.T. , HEMINGWAY J.D. , GOULDING K.W.T. , HOWARD B.J. 
Published: August 2005

SummaryCation exchange resin saturated with H+ and Ca2+ was used to extract 137Cs from peat soil at two sites in Britain affected by l37Cs deposition following the Chernobyl accident. The technique identified three classes of 137Cs, similar to those observed for K+ in soils: ‘Fast’, ‘Intermediate’ and ‘Slow’. These classes are probably related to the selectivity for 137Cs of the cation exchange sites on the organic matter and the clay minerals, and to the structure of the soil. With one exception, most 137Cs was in the ‘Slow’ form and was only very slowly released to the resins, if at all. However, there was enough l37Cs in the ‘Fast’ and ‘Intermediate’ forms to contaminate pasture and thus grazing animals for some years. Based on the resin technique, it is estimated that contamination will persist for several decades in uplands contaminated at these activity concentrations.