bluuebunny/crossref_metadata_2025_split huggingface dataset:
The effect of bulk density, water content and soil type on the diffusion of chloride in soil
Authors: SO H. B. , NYE P. H. 
Published: July 2006

SUMMARYThe relative importance of soil bulk density, water content and potential on the self‐diffusion and impedance factors of 36C1 in a sandy loam and loamy clay were studied. The soil bulk densities used represented a range of conditions from freshly tilled seedbeds to compacted soils. The volumetric water contents and pF were the main factors controlling the soil impedance factors, with bulk density making a small but significant contribution.Soil type affects the impedance factors through differences in anion exclusion volumes, the water contents of poorly connected pores that contribute little to the diffusion process, and tortuosity of the diffusion pathways.
Three approaches to the simulation of the self‐diffusion and non‐instantaneous isotopic exchange of phosphate in soil
Authors: STAUNTON S. , NYE P. H. 
Published: July 2006

SUMMARYThree models of the self‐diffusion of phosphate in moist soil are presented, and their predictions compared to experimental data. The latter appeared to show that isotopic exchange was limited by access to exchange sites. The apparent rate of access was first described by a series of first‐order reactions, then as the diffusion of isotope into, and within, uniformly distributed, porous spherical aggregates, where the majority of exchange sites were situated, and finally as an Nth order (N 1) reversible reaction. All models were solved using Crank‐Nicolson finite difference methods.The first two gave similar predictions; they were not capable of giving an adequate fit to experimental results. The third, although purely an empirical model, not based on a possible mechanism, was able to simulate data well.The mechanistic implications of each model, and of its relative success in simulating phosphate diffusion are discussed.
A rapid method for predicting the lime requirement of acidic temperate soils with widely varying organic matter contents. II. Testing the lime requirement model
Authors: BAILEY J. S. , STEVENS R. J. , KILPATRICK D. J. 
Published: July 2006

SUMMARYA model for predicting lime requirement (Bailey et al., 1989) was tested using data from independent liming experiments on soils from Northern Ireland and New Zealand. Lime requirements predicted by the model were also compared with those obtained by the methods currently used by the Department of Agriculture for Northern Ireland and by the Ministry of Agriculture, Fisheries and Food in England and Wales.The model predicted lime requirement precisely for the independent set of soils from Northern Ireland, and was as reliable at predicting lime requirement for New Zealand soils as the best of seven other quick‐test methods. The model was more reliable at predicting lime requirement for soils from Northern Ireland than the method currently used by the Department of Agriculture for Northern Ireland, and appeared to be as reliable as the method used by the Ministry of Agriculture, Fisheries and Food in England and Wales.
Molecular weight distribution of soil organic phosphorus under irrigated pasture in New Zealand
Authors: CONDRON L. M. , GOH K. M. 
Published: July 2006

SUMMARYGel filtration chormatography (Sephadex G‐100) was used to examine the combined effects of time and single superphosphate fertilizer application on the molecular weight distribution of organic phosphorus (P) extracted from soils under irrigated pasture. Results showed that while most (61‐83%) of the extracted organic P was present in the low molecular weight fraction (i.e. < 100 000 MW), the proportion of high molecular weight organic P (i.e. > 100 000 MW) increased with time from 17‐19% in 1958 to 38‐39% in 1983. Furthermore, organic P, which accumulated in the soil as a result of annual P fertilizer additions appeared to be evenly distributed between the low and high molecular weight fractions.
A simplified analysis of soil water flow to a mole drain
Authors: SCOTTER D. R. , HENG L. K. , HORNE D. J. , WHITE R. E. 
Published: July 2006

SUMMARYAn analysis is described which allows transient mole‐drain flow, surface runoff and water table depth to be computed, given measured or assumed values for rainfall, evaporation, deep percolation, mole‐drain spacing and depth, surface detention, the drainage coefficient, and the saturated hydraulic conductivity, total porosity and macroporosity of the topsoil and subsoil. Dupuit‐Forchheimer flow below the water table and vertical hydraulic potential equilibrium above the water table are assumed. The analysis was successfully tested by simulating the hydrographs from a mole‐pipe drained silt loam, and comparing the results with the measured hydrographs for three contrasting rainfall events.
Frost action in clay soils. I. A temperature‐step and equilibrate differential scanning calorimeter technique for unfrozen water content determinations below 0°C
Authors: BROWN S. C. , PAYNE D. 
Published: July 2006

SUMMARYA modified differential scanning calorimeter procedure was used to determine the relationship between temperature and unfrozen water content (UWC) in seven clays between 0°C and – 15°C to – 24°C. The procedure, which involved nucleation by a cooling followed by a rapid warming to – 0.l°C, avoided the difficulty of supercooling. Problems caused by temperature lag between the sample and its holder and by slowness of water movement within the sample, important even when cooling clay samples of about 17 mm3 at a rate of 0.31 K min−1, were overcome by cooling in a stepwise fashion which allowed time for equilibration between each temperature step. The clays studied included sodium and calcium Wyoming bentonites, < 1 μm and 1–2 pm fractions of St Austell kaolinite and three subsoil clays from England. After nucleation and as temperature fell below OT, water froze in two stages in most of the clays. UWCs at the minimum temperatures reached were up to 38% for the bentonites, between 9% and 20% for the subsoil clays and <4% for the kaolinites.
A critical evaluation of the factors influencing the dissolution of Gafsa phosphate rock
Authors: ROBINSON J. S. , SYERS J. K. 
Published: July 2006

SUMMARYA carbonate‐substituted phosphate rock (Gafsa, GPR) was allowed to dissolve in the presence of one or more of the following: an acid pH buffer (a source of protons), hydrous ferric oxide gel (Fe gel, a sink for P), and a cation exchange membrane (CEM, a sink for calcium). This allowed a quantitative evaluation of the individual and combined influences of three of the most important soil‐related factors (pH, P sink, and Ca sink) which control phosphate rock (PR) dissolution in soils.At 44 d, pH alone (pH 6.1 compared to 4.5) had little effect on the extent of dissolution (1.5 and 6.0% dissolution of P, respectively), probably because of the Ca common‐ion effect resulting from the preferential dissolution of the more‐soluble CaCO, accessory phase. The inclusion of a P sink at pH 6.2 resulted in only a 3.2% dissolution of P after 44 d, whereas at pH 4.5 it increased dissolution from 6.0% to 9.8%. This suggests that pH and P sorption have an interactive effect in influencing GPR dissolution.Inclusion of a Ca sink had the largest influence on GPR dissolution. This was due to the ability of the Ca sink to remove accessory CaCO2. At pH 6.2 the dissolution of P was 10 times larger in the presence of a Ca sink than it was in the presence of a P sink. Despite the smaller ratio of Ca sink size to GPR‐Ca content relative to that of the P sink size to GPR‐P content, the Ca sink was more effective in promoting GPR dissolution. The presence of the Ca sink resulted in twice as much dissolution of P at pH 4.5 than at pH 6.5. At pH 4.5, and in the presence of both the Ca sink and the P sink, 95% dissolution of GPR occurred over the 44‐d experimental period.
Influence of natural and synthetic humic substances on the activity of urease
Authors: VAUGHAN D. , ORD B. G. 
Published: July 2006

SUMMARYThe activity of a purified urease, obtained from Bacillus pasteurii, was inhibited by humic and fulvic acids obtained from an agricultural soil. Enzyme kinetic studies showed that the humic substances affected the affinity of the enzyme for its substrate (Km) and the maximum velocity of the reaction (Vmax). The Vmax was inhibited to the same extent by both humic (HA) and fulvic (FA) acids, the precise effect depending on the pH and concentration of humic substance. At pH 4.0, HA concentrations of 25 pg cm−3 and 10 μg cm−3 inhibited the Vmax by 38.5% and 20% respectively. HA and FA had similar effects on the Km but in this case the lowering of the affinity of the enzyme for its substrate was not concentration dependent in the range 0–25 μg cm−3 of humic substance. Typically, the affinity was decreased from a KM of 50 mM in the control to 67 mM in the presence of HA and FA.The effects were not due primarily to the ash or N contents of the humic substances because de‐ashed humic acid and synthetic model humic (made from catechol, guaiacol, pyrogallol, resorcinol and protocatechuic acid) and fulvic acid (made from polymaleic acid), containing virtually no ash or N, were equally as effective. The effect was not related to the phenolic monomers which, before polymerization, had no effect on urease activity.
Characterization of the Fe(III)—fulvic acid reaction by Mössbauer spectroscopy
Authors: GOODMAN B. A. , CHESHIRE M. V. , CHADWICK J. 
Published: July 2006

SUMMARYFulvic acids have been isolated from a sandy loam (Countesswells series) and a clay soil (Tipperty series) and the products of their reaction with different amounts of iron over a range of pH from 0.5 to 11 analyzed by Mössbauer spectroscopy. Three distinct types of spectral component were detected at 77 K, a sextet from magnetically dilute Fe(III) and doublets from Fe(II) and Fe(III), the last arising from both organic complexes and poorly crystalline oxide species.In iron‐fulvic acid mixtures the proportion of iron as Fe(II) increased as the pH was lowered from 5 to 1 by the addition of hydrochloric or nitric acid at all Fe to fulvic acid ratios (1:5 to 1:500). When the pH was lowered below 1 the amounts of Fe(II) decreased with the lower Fe to fulvic acid ratios, but increased with the higher ratios. The amounts of the Fe(III) component contributing to a doublet signal decreased with decreasing Fe:fulvic acid ratios.At low iron concentrations the iron appears to be strongly bound to the fulvic acid, but when the iron content is of the order of 1–2% uncomplexed Fe(III) species can be present. At pH > 2 these are hydrolysed ions which form poorly‐crystalline oxides at higher pH. This was confirmed by analysis of spectra at 4.2 K. At pH < 2 free ions are present in solution.In solutions with high fulvic acid contents (greater than 100‐fold excess) the reactions with iron are completely reversible, but in solutions with a lower proportion of fulvic acid to iron, where free ions are present, there is a lack of reversibility.
Measuring the diffusion coefficients or rhizosphere exudates in soil. II. The diffusion of sorbing compounds
Authors: DARRAH P. R. 
Published: July 2006

SUMMARYA mathematical model was developed which was capable of simulating the diffusion of compounds with a concentration‐dependent diffusion coefficient, by virtue of their sorption on the solid phase of the soil. Methods were developed which allowed the sorption characteristics and the effective diffusion coefficient of several organic compounds to be inferred from their measured diffusion profiles.
Comparison of various methods for the determination of specific surfaces of sub soils
Authors: CHURCHMAN G. J. , BURKE C. M. , PARFITT R. L. 
Published: July 2006

SUMMARYRetention of ethylene glycol monoethylether (EGME) and ethylene glycol (EG), and sorption of nitrogen and water vapour, were studied on a wide range of soils from New Zealand and Fiji. EGME retention was mainly affected by the amount of EGME liquid present in the desiccator, the interaction with the desiccant (CaCl2), the amount of residual water in the samples, and the time taken to establish end‐points. The extent to which each of these factors influences the weight of EGME retained was different for each sample. Surface areas from nitrogen sorption (BET) were not related to those derived from EGME retention in the same way for all soils; EGME retentions did not vary systematically with clay mineralogy. A constant conversion factor cannot be used to convert retentions of polar liquids (EGME, water and EG) to specific surface values, and retention data by itself cannot be used to measure the absolute surface areas of soils.
Evaluation of porous cup soil‐water samplers under controlled field conditions: comparison of ceramic and PTFE cups
Authors: BEIER C. , HANSEN K. 
Published: July 2006

SUMMARYThe value of soil water samples used in ecological studies is highly dependent on the quality of the samplers. Tension soil‐water samplers are widely used to extract soil solutions, and the samplers are often tested in the laboratory under conditions that differ significantly from field conditions. This study describes a field procedure useful for comparison of two different tension soil‐water samplers. Ceramic and PTFE cups are compared. There were no differences in the concentrations sampled by the two different types of sampler for Na+, K+, Ca2+, Al3+, NH4+, H+ and NPOC (non‐purgeable organic carbon). Change in the applied vacuum in the range 0 to –0.4 × 105 Pa did not change the concentrations of chemical species in the collected soil water. The ceramic cups collected significantly larger amounts of water due to differences in the hydrostatic characteristics of the two samplers. It was found that the ceramic samplers collected the highest concentrations of Mg2+ in some situations. The results are evaluated and discussed in relation to the possible sources of errors and the temporal and spatial variabilities.
Forms of soluble aluminium in acidic topsoils estimated by ion chromatography and 8‐hydroxyquinoline and their correlation with growth of subterranean clover
Authors: WHITTEN M G. , RITCHIE G. S. P. , WILLETT I. R. 
Published: July 2006

SUMMARYLabile Al in the soil solution measured by 8‐hydroxyquinoline (AlHQ) was a better predictor of plant growth than trivalent Al (AlIC3+) measured by ion chromatography (IC). HQ reacted with some organic Al complexes which did not separate during chromatography. In the presence of oxalic acid, AlHQ was greater than AlIC3+, which was the same as the greater than Al3+ (Al3+Calc), whereas in the presence of citric acid, AlHQ was greater than AlIC3+, and both were greater than Al+3Calc, In extracts of soils that had been acidified, Al3+IC was less than AlHQ, which was similar to Al3+Calc, when it was assumed that the only complexing ligands were OH− and F−. The proportion of Al3+IC in the soil solutions decreased more than AlHQ as the pH increased. Organic ligands appeared to form complexes with Al at the expense of AIF complexes. Forms of Al detected by IC differed in CaCl2 extracts and soil solutions. AlHQ in the CaCl2 extracts and soil solution were closely correlated, although the proportion of AlHQ was higher in the CaCl2 extracts. And soil solutions. AlHQ in the CaCl2 extracts and soil solution were closely correlated, although the proportion of AlHQ was higher in the CaCl2 extracts.
The effects of pH and chloride concentration on mercury sorption. II. By a soil
Authors: BARROW N. J. , COX V. C. 
Published: July 2006

SUMMARYThe pH of a soil was altered by incubation with either acid or lime, and the sorption of mercury was measured in the absence of chloride and at three chloride concentrations. In the absence of chloride there were only small effects of pH on sorption between pH 4 and 6; sorption decreased at higher pH. Addition of chloride decreased sorption at low pH but had little effect on sorption at high pH. Consequently, in the presence of chloride, sorption increased with increasing pH between pH 4 and 6 and then decreased. Many of the mercury sorption curves were sigmoid. This was explained by assuming that a small amount of complexing material was present in the solution after mixing with the soil. Calculation of the mercury species present in solution was made difficult by uncertainties about the postulated complexing material. Nevertheless, between pH 4 and pH 5.8, it was possible to explain the effects of pH and of chloride concentration on sorption as entirely due to changes in the HgOH+ concentration.
Nature of soil carbohydrate and its association with soil humic substances
Authors: CHESHIRE M. V. , RUSSELL J. D. , FRASER A. R. , BRACEWELL J. M. , ROBERTSONS G. W. , BENZING‐PURDIE L. M. , RATCLIFFE C. I. , RIPMEESTER J. A. , GOODMAN B. A. 
Published: July 2006

SUMMARYThe fulvic acid and alkali‐soluble polysaccharide fractions of a sandy loam arable soil of the Countesswells series have been subjected to acid hydrolysis or methylation and the products examined by infra‐red and NMR spectroscopy, pyrolysis mass spectrometry and chemical analysis. Infra‐red and NMR spectroscopy of the polysaccharide fraction indicated that the substance was predominantly carbohydrate, although sugars accounted for less than one‐third of the weight by chemical analysis. Pyrolysis mass spectrometry con‐firmed the presence of sugars by sugar anhydride formation, but also showed the presence of ‘secondary’ or ‘pseudo’ polysaccharide. The fulvic acid contained only 2–3% sugars by chemical analysis, whereas a much larger carbohydrate component was suggested by physicochemical analyses. Infra‐red and pyrolysis mass spectrometry difference spectra for the residues after acid hydrolysis indicated the release of material with some of the characteristics of glycoprotein. Most of the carbohydrate present in the fulvic acid was of the secondary or pseudo polysaccharide type. The hypothesis that the secondary polysaccharide could be a degraded polysaccharide structure in which some sugar residues have been partly transformed to melanoidins by Maillard reaction is explored.
The physical and chemical composition of mounds of Macrotermes carbonarius (Hagen) (Termitidae, Macrotermitinae), in Penang, Malaysia
Authors: McCOMIE L. D. , DHANARAJAN G. 
Published: July 2006

SUMMARYThe mound of the fungus‐growing termite Macrotermes carbonarius (Hagen) contained significantly larger proportions of clay (P<0.05) than the adjacent soil. The largest clay content was found in the brood chamber. Concentrations of organic carbon, nitrogen, potassium and calcium in various parts of the mound were enriched compared to the adjacent soil at 10–40 cm depth from which they might have been derived. The activities of M. carbonarius did not significantly alter the pH or the bulk density of the mound soil compared to the adjacent topsoil.
Fragipan formation in argillic brown earths (Fragiudalfs) of the Milfield Plain, north‐east England. II. Post Devensian developmental processes and the origin of fragipan consistence
Authors: PAYTON R. W. 
Published: July 2006

SUMMARYPedogenetic processes following a permafrost stage of development in four argillic brown earths with fragipans (Glossic and Ochreptic Fragiudalfs) are investigated by soil microscopy, including SEM observations of unimpregnated soil material, and by determination of clay mineralogy. Micromorphology of the apparently massive fragipan confirms both the presence of subhorizontal fissures infilled with illuvial deposits separating dense lenticular structures formed by ice‐lens growth, and former vertical fissures formed by dessication on freezing with subsequent widening by ice‐vein development. The firmness and brittle failure of the fragipans are attributed to a closely‐packed, well‐graded matrix of skeleton grains bonded by clay bridges consisting of non‐swelling illite and chlorite and to weak interconnection of macrovoids. Weak cementation is rejected as an explanation of fragipan consistence. Sequential stages of particle translocation have been critical to fragipan formation. High bulk density is attributed not only to irregular compression and contraction of the soil matrix under permafrost conditions but also to the infilling of voids by illuvial silt and clay. The full development of the fragipans has depended on Flandrian clay migration which has contributed to clay‐bridge formation, void infilling and localized seasonal impedance of drainage resulting in eluviation of iron oxides, the development of grey polygonal patterning, and processes of degradation at the pan surface leading to glossic features.
Structural collapse and strength of some Australian soils in relation to hard setting: II. Tensile strength of collapsed aggregates
Authors: GUSLI S. , CASS A. , MACLEOD D.A. , BLACKWELL P.S. 
Published: July 2006

SummaryThe strength of soils is related to structural stability. Aggregate structure which collapses on wetting may set to a hard, consolidated layer on drying (hard setting). This process may be moderated by suction wetting and possibly by application of calcium, but the mechanism of moderation is not clear. We investigated the collapse‐strength relationship and the mechanism by which wetting method and calcium act to reduce strength in hard setting and non‐hard setting soils. Indirect tensile strength of aggregate beds that had been wetted with water or 10mM CaCI2 by rapid flooding or at a suction of 200 mm, was measured after draining to various suctions and drying at 40°C.The greater the volume strain during wetting and draining, the greater the tensile strength. Beds that were suction wetted, either with water or calcium solution, showed minimal collapse and did not develop high strength on drying. Water‐flooded beds had the greatest dry strength while beds flooded with calcium solution developed significantly lower strength. The critical factor determining tensile strength of the beds appeared to be the presence of large (>75 μm diameter) pores. The greater the volume strain on wetting, the smaller the proportion of larger pores and the greater the tensile strength on drying. Flood wetting caused more loss of large pores and closer packing of particles. Wetting with calcium solution did not affect the degree of collapse compared with that of water alone but did produce beds with larger pores than when wetted with water. Consequently the strength of the calcium‐wetted beds was lower.
Changes in the chemistry of soil solution and acetic‐acid extractable P following different types of freeze/thaw episodes
Authors: VAZ M.D. RON , EDWARDS A.C. , SHAND C.A. , CRESSER M.S. 
Published: July 2006

SummaryFreezing significantly influences the amount and chemical form of extractable soil phosphorus and, therefore, has important consequences regarding plant nutrient availability. Much of the current evidence relies on field‐based observations and tends to be rather contradictory. The present work reports the specific effects various freezing episodes have on phosphorus availability. Experimental treatments included the freezing rate and the time soil remained frozen together with the number of freeze/thaw cycles. These laboratory incubations used two soils, an iron humus podzol and a peaty podzol, sub‐samples of which were equilibrated at three different soil‐moisture contents. Concentrations of phosphorus in soil solutions and acetic acid extracts (Ac‐P) were measured. Freezing had the greatest effect on the organic (Op) horizon of the peaty podzol, where the amounts of total dissolved phosphorus (TDP) and Ac‐P increased from 0.58 to 3.21 and from 11.8 to 19.3 mg P kg−1, respectively. TDP in soil solution was subdivided into three broad categories, dissolved (molybdate) reactive (MRP), organic (DOP) and condensed (DCP). The rather variable effect that freeze/thaw episodes had on these fractions highlighted the problems associated with attributing the ‘freezing effect’ to any single process.