bluuebunny/crossref_metadata_2025 huggingface dataset:
Non‐destructive separation of discrete pedogenic features from soils
Authors: KANE P. , MOTT C. J. B.
Published: July 2006

A general method for the non‐destructive separation of discrete pedogenic features that is suitable for use with a wide range of soil types is presented. Controlled slaking of soil peds is used to achieve separation between structurally coherent features and less organized matrix material. A slaking, stabilization and sieving sequence is repeated a number of times until the matrix material has been removed. The advantages and limitations of the method are outlined and a number of applications illustrated.
Electric charge characteristics of horizons of Ando (B) and Red‐Yellow B soils and weathered pumices
Authors: OKAMURA YUTAKA , WADA KOJI
Published: July 2006

The electric charge characteristics of five Ando (B) and two Red‐Yellow B horizon soils and two weathered pumices were studied by measuring the retention of NH4+ and Cl− at different pH values and NH4Cl concentrations. The magnitude of their negative charge (CEC; meq/100g) was dependent on pH and NH4Cl concentration (C; m) as represented by a regression equation: log CEC =apH +blog C +c. The values of the coefficient a (0.017 to 0.342), b (0.031 to 0.274) and c (1.41 to − 1.26) were correlated and depended on the kind of clay minerals present. A similar equation: log AEC =a’ pH +b’ log C+c’ was also found for the positive charge in the Ando soils, but there was little difference in the values of a’(−0.204 to −0.251), b’(0.181 to 0.253) and c’(2.06 to 2.46) between the soils. It was shown that the equations generally hold for soils with constant and/or variable charges and describe adsorption equilibria in which NH4+ and H+, and Cl− and OH− compete for cation‐ and anionexchange sites, respectively. The significance and utility of the coefficients is discussed.
The effect of pH on the total and free ionic concentrations of mnganese, zinc and cobalt in soil solutions
Authors: SANDERS J. R.
Published: July 2006

Samples of five soils whose pH in the field had been adjusted to between 5.0 and 7.5 were incubated with water or 0.01 m CaCl2 at 90% field capacity. Additional samples of the most acid soil were limed to various pH values immediately before incubation.

Manganese, zinc and cobalt concentrations in the soil solutions, collected by displacement, decreased as the pH increased; the concentrations in calcium chloride solutions were higher than those in water solutions. The free divalent ions Mn2+, Zn2+ and Co2+ were the major metal species in solution at pH 5 but the proportion of the metals present as the free ion decreased as the pH increased.

Differences in the manganese and zinc concentrations in the solutions were due not only to the pH of these solutions but also to the original pH of the soil in the field.
Kinetics and temperature relationships of mineralization and nitrification in Rothamsted soils with differing histories
Authors: ADDISCOTT T. M.
Published: July 2006

Mineralization of soil organic nitrogen measured in laboratory incubation experiments on Rothamsted soils with contrasting histories was most appropriately expressed by the simple zero‐order relationship Nt=kt in which Nt is the amount of N mineralized in time t. The rate constants (k) were well related to the absolute temperature by the Arrhenius equation. The approach in which ‘potentially mineralizable N’ (N0) is mineralized with first‐order kinetics could not be applied to these data.

When the soils were incubated with added ammonium chloride, the increase in nitrate‐N and the decline in ammonium‐N were both linear with time, but were equal to each other in only one of the soils. These linear relationships did not reflect true zero‐order kinetics because the rates of ammonium‐N decline and nitrate‐N production both depended on the initial ammonium concentration. The Arrhenius relationships showed no significant difference between mineralization and nitrification in their sensitivity to temperature.
Variation in yield between two similar sandy loam soils. II. Causes of yield variation in cabbage and lettuce crops
Authors: COSTIGAN P. A. , McBURNEY T.
Published: July 2006

Three experiments were conducted to discover the causes of difference in yields of cabbage and lettuce when grown on two similar sandy loam soils.

In a glasshouse experiment the growth of lettuce was the same on both soils provided the soil was moist and had sufficient thoroughly incorporated fertilizer. Sowing the seeds of cabbage in small pockets of compost in the seedbed increased growth on both sites by about 25%. Placement of a large amount of extra fertilizer about 10cm below the drill line imporved growth on the poor site only.

A third experiment followed the development of the yield difference in a lettuce crop. An 86% difference in potassium concentration was recorded even before emergence. This was followed by a reduction in lateral root growth on the poor site and subsequently by a lower relative growth rate from emergence until about 40 days from sowing.

In conclusion, the growth on the poor site was limited because the amount of native soil potassium was madequate for the needs of the developing seedlings and the fertilizer granules could supply potassium to only a small proportion of seedlings.
Gas diffusion through soil crumbs: the effects of compaction and wetting
Authors: CURRIE J. A.
Published: July 2006

Samples of 1–2 mm crumbs from a clay loam under permanent pasture were equilibrated at ‐5 kPa water potential then compacted to varying degrees. Gas diffusion coefficients D, (hydrogen through air), were measured immediately on compaction, again after re‐equilibration at ‐5 kPa, then at other water contents between saturation and dryness. The relationship between diffusion coefficient and air content, was, as elsewhere, in two parts (dD/d small for drainage of pores within crumbs; large for pores between crumbs), but the transition from one part to the other occurred at smaller air contents with increased compaction. The air content at which D approached zero as the samples wetted was greatest in the loosest soil. Compaction from a bulk density of 0.86–1.29 g cm−3 decreased the relative diffusion coefficient, D/D0 (D0 is the diffusion coefficient without impedance), from 0.35 to 0.22 (by 38%) at complete dryness, but from 0.19 to 0.035 (by 82%) in the soil initially at ‐5 kPa. On re‐wetting and re‐equilibrating at −5 kPa, D/D0 decreased further to 0.008 (total 97%) because of extra water held in the now smaller pores of the compacted soil.

No single relationship between D/D0 and fitted the results for even this one soil.
Estimation of the total gaseous nitrogen losses from clay soils under laboratory and field conditions
Authors: COLBOURN P. , IQBAL M. M. , HARPER I. W.
Published: July 2006

Acetylene blockage was evaluated as a method for measuring losses of N2O + N2 from two Denchworth series clay soils. The denitrification potential in anaerobic, dark incubations at 20°C with nitrate (equivalent to 100 kg N ha−1 0–20 cm depth), maximum water holding capacity, and acetylene (1%), was equivalent to 32 ± 11 and 39 ± 6 kg N ha−1 per day for the two 0–20 cm soils and was positively correlated with carbon content (r= 0.98). After 4 days N2O was reduced to N2 in the presence of C2H2.

In April 1980 following irrigation (24 mm) and applications of ammonium nitrate (70 kg N ha−1) and acetylene, the mean nitrous oxide flux from soil under permanent grass was 0.05 ± 0.01 kg N2O‐N ha−1 per day for 8 days.

In June 1980, the losses of nitrogen from cultivated soils under winter wheat after irrigation (36 mm) and acetylene treatment were 0.006 ± 0.002 and 0.04–0.07 ± 0.01 kg N ha−1 per day respectively before and after fertilizer application (70 kg N ha−1). The nitrous oxide flux in the presence of acetylene decreased briefly, indicating that nitrification was rate determining in drying soil.
Use of alkaline soil extracts for 13C n.m.r. characterization of humic substances
Authors: NEWMAN R. H. , TATE K. R.
Published: July 2006

Previous solution 13C n.m.r. studies of soil organic matter have been confined to isolated humic or fulvic acid fractions. A study of 10 crude alkaline extracts from five New Zealand topsoils has now shown that such purification is unnecessary. Spectra were not noticeably broadened by co‐extracted iron in concentrations up to 2 mg cm−3. Optimized pulse parameters were similar to those reported for a solution of a purified humic acid. Relaxation results support a generalized model for humic material, in which aromatic structures, carbohydrates, amino acids and polymethylene chains are linked together to form flexible macromolecules. Relative contributions from each component varied from soil to soil.
Diffuse reflectance infrared spectra of phosphate sorbed on alumina gel
Authors: NANZYO M.
Published: July 2006

Infrared absorption spectra of phosphate sorbed on alumina gel were obtained by subtracting the diffuse reflectance infrared (DRIR) spectra of alumina gel from those of phosphated alumina gel. The positions of the absorption bands due to P·O stretching vibration were little affected by the change in pH and the amount of phosphate sorbed. These absorption bands were similar to those for aluminium phosphate gel. The sorption product of phosphate on alumina gel was amorphous by X‐ray diffraction. Na+ and Cl− adsorption properties of alumina gel tended towards those of aluminium phosphate gel with phosphate sorption. It was concluded that the state of phosphate sorbed on alumina gel is similar to that of aluminium phosphate gel.
The interaction of hydrazine hydrate with humic acid preparations at pH 4
Authors: ISAACSON P. J. , HAYES M. H. B.
Published: July 2006

Sorption isotherms were obtained by a continuous‐flow method for the interaction of hydrazine hydrate with freeze‐dried hydrogen‐, aluminium‐ and calcium‐exchanged humic acid preparations in aqueous suspensions at pH 4. The application of the continuous‐flow method is outlined and the fit of the isotherms to three sorption equations is examined. Microcalorimetry was used to measure directly the differential enthalpies of reaction as functions of sorptive concentrations. Exchange by hydrazinium ions of the exchangeable cations on the humates, chemisorption by interaction of hydrazine with humate carbonyl groups, and non‐specific sorption involving weakly‐ and strongly‐held hydrazinium ions and hydrazine molecules are shown to be the major sorption processes in these systems. The relative importance of each of these processes for the different hydrazine/humate systems is discussed, and the influence of the exchangeable cation on humate reactivity is considered.
Determination of CEC and exchangeable Ca and Mg in non‐saline calcareous soils
Authors: MISOPOLINOS N. D. , KALOVOULOS J. M.
Published: July 2006

A method is proposed for determination of CEC and exchangeable cations in non‐saline calcareous soils. The saturating solution used, 0.5 d Lithium formate in 80% methanol at pH 8.2, does not dissolve CaCO3.The method is simple and less laborious than any other known method.
Modelling water flow through undisturbed soil cores using a transfer function model derived from 3HOH and Cl transport
Authors: WHITE R.E. , THOMAS G. W. , SMITH M.S.
Published: July 2006

Large undisturbed soil cores (20 cm diam. × 25–30 cm long) were irrigated at rates of 0.5–4 cm h−1 with 0.005 M CaCl2 solution labelled with 3HOH. The cores were used at varying initial water contents and flow in all cases was unsaturated. Breakthrough curves for Cl and 3HOH were markedly asymmetric and unlike those reported for columns of packed aggregates. The data could be satisfactorily described using a density distribution function of the logarithm of cumulative drainage D. The mean and standard deviation of In D were estimated by a curve‐fitting procedure from Cl and 3HOH effluent concentrations in each core. The mean pore water velocity and fraction of the soil water that participated in solute transport (the mobile volume) were also calculated.

The apparent velocity of Cl movement was always greater than that of 3HOH which suggested that the mobile volume involved in convective and diffusive transport of Cl was less than that for 3HOH. We suggest that Cl and 3HOH diffused at different rates out of flowing water films in a relatively few large conducting channels into essentially immobile water within the surrounding soil matrix. The difference in mobile volume for Cl and 3HOH was used to calculate the perimeter of voids in any horizontal cross‐section of the soil through which water flowed, assuming a planar interface between the mobile and immobile water.
Fate of fertilizer nitrogen applied to grassland. II. Nitrogen‐15 leaching results
Authors: BARRACLOUGH D. , GEENS E. L. , MAGGS J. M.
Published: July 2006

Results are presented from a 3‐year investigation into nitrate leaching from grassed monolith lysimeters treated with double (15NH415NO3) or single (15NH4NO3) labelled ammonium nitrate at three rates, 250, 500 and 900 kg N ha−1 a−1. Over the 3 years of the experiment, 0.14%, 3.1% and 18.1% of the applied fertilizer was recovered in the leachate at 250, 500 and 900kg N ha−1 respectively. This represented 9%, 39% and 75% of the overall nitrate leaching at the three application rates. A significant proportion of the fertilizer leached as nitrate at the three application rates was derived, via nitrification, from the fertilizer ammonium. Increasing fertilizer applications caused a rise in the leaching of both soil and fertilizer derived nitrogen, although whether the increase reflected a true priming effect was not clear.
Detection of aluminium coordination in soils and clay fractions using27 Al magic angle spinning n.m.r.
Authors: WILSON M. A. , BARRON P. F. , CAMPBELL A. S.
Published: July 2006

Preliminary studies using 27Al n.m.r. of well characterized size fractions containing imogolite from an Andosol are reported. They demonstrate that 27Al n.m.r. is a useful complementary tool to X‐ray fluorescence methods for the detection of four‐and six‐fold co‐ordination of aluminium in soils. Whereas the X‐ray method depends on interpolating between standards, this is unnecessary in the n.m.r. method since four‐ and six‐fold coordinated aluminium are clearly resolved. The results demonstrate how aluminium co‐ordination changes in size fractions from the Andosol and confirm that all aluminium in imogolite is in six‐fold co‐ordination. It is also suggested that the Al‐O bond distance in imogolite is 1.82 A.
Fulvic acids: structure and metal binding
Authors: MURRAY K. , LINDER P. W.
Published: July 2006

Equilibrium calculations have been carried out at 25°C and an ionic strength of 0.04 to determine the predominant metal binding sites on a well‐characterized fulvic acid for magnesium(ll), calcium(ll), manganese(ll), iron(lll), copper(ll) and zinc(II). Statistical estimates of the concentration of 14 sites are obtained from a random molecular model of fulvic acid. Protonation and metal formation constants are estimated from those of simple model ligands and corrected to the above conditions. Results indicate the importance of phthalate sites for all metals except iron(III), salicylate sites for iron(lll) and acetylacetonate sites for copper(ll). Iron (III) ions are found to form ML2 type complexes extensively. The affinity of the metal ions for fulvic acid as a whole is found to decrease in the order iron(III) > copper(II) > zinc(II) > manganese(Il) > calcium(II) > magnesium (II).
Calculation of the field volumetric water content of cracking clay soils from measurements of gravimetric water content and bulk density
Authors: HACK H.R. B.
Published: July 2006

Uncertainty in estimating water use in shrinking soils from changes in gravimetric water content arises from the difficulty in ensuring that samples are taken from comparable depths at different sampling times, and of identifying the correct bulk density for the conversion to volumetric water content.

Equations which express the amount of water held by the same mass of soil solid matter during soil drying and shrinking are derived for two models. In one the soil properties vary continuously with depth and in the other the values are averages for layers. The models are applied to field water content measurements made in the Sudan Gezira. Systematic errors (biases) are examined and their magnitudes calculated. The maximum overestimate of gravimetric water content arising from ignoring vertical shrinkage on drying was 2.3%. The maximum overestimate of volumetric water content from ignoring volumetric contraction was 24%; this was corrected by using for all sampling times bulk densities of layers before contraction.
Seasonal variations in soil erodibility under different land‐use types in Luxembourg
Authors: IMESON A. C. , VIS M.
Published: July 2006

Soil erodibility measurements for detachment by raindrop impact were made on samples collected at monthly intervals from forest, pasture and farmland sites. All sites exhibited strong seasonal variations in erodibility with maximum values occurring during the winter and minimum values in the summer. The relative erodibility of the different soils is described and the field and laboratory methods used are compared. The best time for sampling the soil for soil erodibility determinations is indicated.

Erodibility is estimated from laboratory simulation experiments on undisturbed samples, from aggregate stability determinations and from field measurements with splash boards.
Proto‐imogolite allophane in podzol concretions in Australia: possible relationship to aluminous ferrallitic (lateritic) cementation
Authors: FARMER V. C. , FRASER A. R. , ROBERTSON L. , SLEEMAN J. R.
Published: July 2006

Proto‐imogolite allophane was found in amounts ranging from 1% to 5% in concretions and ortstein from several sandy podzols in Australia. Micromorphological observations on concretions in which allophane was the dominant clay component indicated that it had been deposited in layers during successive drying episodes to form a yellow, glassy, weakly anisotropic, fluorescent cement around sand grains. Iron oxides and organic matter were minor components of the cement. It is proposed that a proto‐imogolite sol is the mobile phase that deposits Al and Si in these concretions, and that the proto‐imogolite allophane could be a precursor of kaolinite in older concretions, and of gibbsite in leaching environments. Proto‐imogolite sols and allophane could play a similar role in the pedogenesis of kaolinite and gibbsite in concretions in freely drained ferrallitic soils.
Effect of metal toxicity on the size of the soil microbial biomass
Authors: BROOKES P. C. , McGRATH S. P.
Published: July 2006

The amount of soil microbial biomass was measured by the chloroform fumigation technique on agricultural soils which had been previously treated with different bulky organic manures. Amounts of soil microbial biomass in soils receiving sewage sludge or sludge‐containing composts were much smaller than in soils which received farmyard manure over the same period. This effect was attributed to the toxic metals present in the sludges and was readily detectable more than 20 years after the last sludge application.
The effect of mineral weathering and soil solution concentration on ESR—SAR relationships of arid and semi‐arid zone soils from Israel*
Authors: FRENKEL H. , ALPEROVITCH N.
Published: July 2006

ESR—SAR relationships of 623 soil samples from arid and semi‐arid zones in Israel were found to depend on soil salinity and cation exchange capacity as reflected crudely by the saturation percentage. The Gapon constant decreased as salinity increased and, for a given salinity level, it also decreased as the soil saturation percentage (SP) increased. There was no relationship between ESR and SAR for soils with low SP values (20–40) or low salinity levels (0.2–2 dSm−1). Regression equations are presented for different salinity and saturation percentage levels.
Charge properties of mixtures of minerals with variable and constant surface charge
Authors: MADRID L. , DÍAZ E. , CABRERA F.
Published: July 2006

Surface charge of mixtures of lepidocrocite and illite determined by adsorption of potential‐determining and electrolyte ions is studied as a function of pH and NaCl concentration. Deviations between results obtained by both methods were a function of the illite content of the mixtures, and can be mainly attributed to coatings of hydroxyaluminium complexes on the constant charge surfaces of the clay mineral, which can react with H+ ions or release exchange sites by precipitation of well‐formed hydroxides. These coatings of aluminium complexes can cause H+ consumptions similar to those due to lepidocrocite.

Some ideas are put forward for modelling charge properties of mixed systems.
Ammonium‐calcium exchange equilibria in soils and weathered pumices that differ in cationexchange materials
Authors: OKAMURA Y. , WADA K.
Published: July 2006

The retention of NH4+ and Ca2+ on soil and weathered pumice samples containing constant and/or variable charge components was measured in different NH4CI‐CaCl2 solutions. The NH4+/Ca2+ selectivity of each sample was evaluated using a quotient of the partition of NH4+ on the exchange sites and in the solution relative to that of Ca2+. It increased with decreasing pH and increasing NH4Cl‐CaCl2 concentration for a given equivalent fraction of NH4+ in the solution. These effects were quantitatively explained in terms of the changes of NH4+ and Ca2+ concentrations in the solution and in the diffuse double‐layer of the ion‐exchange material as predicted by the law of mass action and the electric double layer theory. The NH4+/Ca2+ selectivity of different exchange materials showed a similar variation among their exchange sites and increased in the order humus, allophane and imogolite (Si/Al ratio 0.5) < allophane (Si/Al ratio 1.0), montmorillonite < vermiculite, illite < halloysite. The origin of negative charge, the steric features around the exchange sites and clay‐humus interaction are suggested as being important in determining the NH4+/Ca2+ selectivity.
Thermodynamics of K‐Ca exchange in soils
Authors: GOULDING K. W. T. , TALIBUDEEN O.
Published: July 2006

Surface soils from six ADAS long‐term experiments, including two on Andover series, were examined for K‐Ca exchange by exchange isotherm and calorimetric methods. Preference for K decreased in the order Worcester > Clwyd > Newport. The latter two acid soils showed ‘no preference’ and Ca preference respectively. Preference for K decreased with decreasing surface area and increasing surface charge density. The enthalpic factor favoured K preference in every soil, but the entropic factor favoured Ca preference in all but one soil. The magnitude of the enthalpic factor was greater than that of the entropic factor, resulting in K preference, in the Andover, Hanslope and Worcester soils, while the reverse was the case in the Newport soil. In the Clwyd soil, enthalpic and entropic forces were counterbalanced. These relative contributions were related to the interactions between clay mineralogy, pH and manurial history.

Differential heat measurements, ‐d (ΔHx)/dx revealed exchange site heterogeneity in five of the soils. Five regions of constant ‐d (ΔHx)/dx were found, ranging from 6 to 12 kJ eq−1, a maximum of three occurring in any one soil. These were assigned to montmorillonite (two regions), mica, hydrous mica and vermiculitic mica surfaces. The 2: 1 phyllosilicate contents of the clay fractions of the whole soils calculated thus differed from those determined by XRD analysis of the clay fractions.

Residual K decreased the cation exchange capacity of some of the soils but did not alter their surface areas. Its effect on K preference, K binding strength and the arrangement of the components of the system (the entropic factor) was complex.
The forms of occurrence of manganese in some acidic soils
Authors: JARVIS S. C.
Published: July 2006

The forms of occurrence of Mn were examined in some acidic surface and sub‐soils from areas of permanent grassland using chemical extractants. Despite high total contents of Mn in some of the soils and low pH, only minor proportions occurred as exchangeable Mn2+. Much larger proportions were present as reducible hydrous oxides, e.g. up to 38% and 54% of the total contents in surface and subsoils, respectively, were present as hydroquinone extractable, or easily reducible, Mn. Reducible forms of Mn were poorly correlated with other more mobile forms. Large proportions of the total Mn contents were accounted for when estimates of different fractions were calculated from differences in amounts extracted by different individual extractants, i.e. M NH4OAc, 0.2% hydroquinone, 0.1 M pyrophosphate, and ammonium oxalate. The distribution of Mn amongst the different fractions as determined by a sequential fractionation scheme differed markedly from the distribution calculated by differences. In particular, there was a marked change in form after extraction with pyrophosphate.
Mineralogical and chemical properties of weathered magnetite grains from lateritic saprolite
Authors: ANAND R. R. , GILKES R. J.
Published: July 2006

Magnetite grains in lateritic saprolite have altered in situ to porous hematite (martite) grains. Hematite occurs as relatively large (∼ 1 μm) platy crystals, triangular arrays of small (0.01–0.05 μm) lathlike crystals and very small (< 100 Å) platy anhedral particles. Titanium increased in altered grains and may substitute for Fe3+ in hematite. Mn, V, Cr and Zn remained approximately constant whereas the Ni content decreased. Halloysite crystallized from soil solution within pores resulting in a marked increase in the Si and Al contents of grains.
Iron oxide mineralogy of placic horizons
Authors: CAMPBELL A. S. , SCHWERTMANN U.
Published: July 2006

The iron oxide mineralogy of 15 placic horizons from Germany, New Zealand, Belgium and U.K. was determined by differential X‐ray diffraction (DXRD). All samples examined contained ferrihydrite and goethite, lepidocrocite occurred in 10, and six contained non‐DCB‐reducible, lithogenic hematite. Ferrihydrite was most readily identified in ‘untreated minus oxalate‐treated’ DXRD patterns. Al‐substitution of goethites ranged from 4 to 13 mole %. Mean crystallite dimensions varied from 11 to 21 nm and from 6 to 21 nm for the goethite (110) and (111) lines respectively, from 7 to 51 nm for the lepidocrocite (020) line (lath thickness), and from 55 to 134 nm for the hematite (104) line. These values are typical for goethites from carbon‐rich environments with poor crystallization conditions, and for well crystalline lithogenic hematites. The DXRD method is ideally suited to the evaluation of the many selective dissolution techniques used in soil chemistry and mineralogy.
Total copper contents of Scottish soils
Authors: REAVES G. A. , BERROW M. L.
Published: July 2006

The distribution of the total copper contents of 4179 samples from 946 Scottish soil profiles is reported and the relation of copper content to some other soil variables is examined.

The frequency distribution of copper contents is found to be approximately lognormal. The derived mean for the full set of data is 10 mg/kg and the normal range 0.93–110 mg/kg.

The copper contents of basic and intermediate igneous rocks exceed those of acidic rocks by a factor of about 5 and among sedimentary rocks copper contents are higher in argillaceous than in arenaceous types.

The general trend is for copper to increase with increasing depth and ash content and to decrease with increasing sand content.

On the basis of total copper content the risk of copper deficiency is assessed to be high in 26 soil associations in Scotland and moderate in a further 10. Naturally occurring copper toxicity is unlikely to be encountered.
Soil development processes in an Aqualf‐Ochrept sequence from loess with admixtures of tephra, New Zealand
Authors: PARFITT R. L. , SAIGUSA M. , EDEN D. N.
Published: July 2006

The properties of contrasting soils occurring under a 1050–1600 mm rainfall gradient are described. The soils range, with increasing rainfall, from Typic Fragiaqualfs to Andic Dystrochrepts. Sand mineralogy of these soils indicates that they have formed in essentially similar parent materials consisting largely of quartzo‐feldspathic loess with admixtures of rhyolitic and andesitic tephra.

The Fragiaqualfs have high bulk density, impeded drainage in winter, degraded chlorite, argillic horizons, halloysite and vermiculite. The Dystrochrepts have lower bulk density, free drainage, ferrihydrite, allophane, humus‐(Al, Fe) complexes and no argillic horizons.

An hypothesis to explain differences between these soil groups proposes that the dense horizons in the Fragiaqualfs arise largely from hydraulic suctions exerted by roots during periods of high summer water deficits. The consequent loss of porosity leads to impeded drainage in winter causing gleying and enhanced clay formation. In the Dystrochrepts the summer deficits are lower, consequently the soils have lower bulk densities and remain free draining.
Quantitative determination of calcite and dolomite in soils by X‐ray diffraction
Authors: ULAS M. , SAYIN M.
Published: July 2006

An X‐ray diffraction method using CaF2 as internal standard was applied to the carbonate‐rich soils of the ukurova and Göksu plains in Southern Turkey. Soil samples, freed from carbonates, were used as matrices and a separate calibration curve was prepared by known carbonate additions for each soil series. Statistical tests showed that one calibration curve was sufficient to determine calcite and dolomite contents of seven soil series. Particle orientation was an important factor for accurate analyses and a test, using the known addition method, should be carried out before using a matrix material other than carbonate‐free soils.
Soil structure and potassium supply. I. The release of potassium from soil aggregates to Ca‐resin
Authors: HEMING S. D. , ROWELL D. L.
Published: July 2006

Potassium release from saturated spherical aggregates of three clay soils to Ca‐resin was measured and compared with release in suspensions (Talibudeen et al., 1978). The diffusion coefficient for K was calculated from measurements of the tortuosity factor using 36Cl, volumetric water content and buffer power. Release of K is in the order: suspensions >2–3 mm > 6–8 mm aggregates. A computer model incorporating diffusion analysis and release of K shows that in the aggregates the rapidly diffusing exchangeable K, Kex, is best measured by the extrapolated intercept of a desorption isotherm (24 h equilibration), and is 8–55% less than that extracted by NH4OAc leaching. Release of K within the aggregates (Knex, a fraction approximating to Talibudeen's peripheral K) is delayed until after about 95% of Kex has been depleted which takes 1–2 days. The effective release rate of Knex inside the aggregates is ∼ 17% less than in soil suspensions. Diffusion imposes only small limitations on the release from aggregates of Knex. This rate of release depends on the frequency of resin changes.
Soil structure and potassium supply. II. The effect of ped size and root density on the supply to plants of exchangeable and non‐exchangeable potassium from a chalky boulder clay soil
Authors: HEMING S. D. , ROWELL D. L.
Published: July 2006

A model based on measurements of potassium release from spherical aggregates (Heming & Rowell, 1985, Part I) has been used to predict release from larger aggregates, for longer times, drier soils and varying diffusion coefficients. The model has been adapted to predict supply to a single root from a soil cylinder and compared with measured uptake by onions. A ‘supply index’ shows likely restrictions in the availability of exchangeable K and in the rate of supply of non‐exchangeable K resulting from diffusion limitations over a 4 week period for (i) aggregates covered with a dense roots system, and (ii) roots growing at known densities. For this period diffusion alone should not limit exchangeable K uptake in the field if the root density is at least 3.5 cm/cm3: at 0.9 cm/cm3 about 50% may be unavailable. The supply rate of non‐exchangeable K increases with root density and may be important for high‐demanding crops in dry seasons.
A basis for soil profile modelling in a geomorphic context
Authors: KIRKBY M. J.
Published: July 2006

A mathematical model for soil profile evolution is developed in three parts; respectively for the weathering profile, the organic profile and for the inorganic profile associated with nutrient cycling. Processes modelled are percolation, equilibrium solution, leaching, ionic diffusion, organic mixing, leaf fall, organic decomposition and mechanical denudation. In each sub‐model some of these processes may be neglected, and time‐scales differ, so that they are best separated. Each leads to a second‐order linear partial differential equation with non‐constant coefficients. Equilibrium profiles are derived for the simplest cases, and numerical models exemplify profile evolution in more realistic cases. Modelled weathering profiles generally show a zone of near‐constant composition at the surface, with saprolite developing in deep profiles. Nutrient‐cycling profiles show the variable development of B‐horizons, and may be classified according to the relative depths of rooting, organic soil, and organic mixing processes.
Complementary use of thermal imagery and spectral analysis of soil properties and wheat yields to reveal cyclic patterns in the Flevopolders
Authors: BURROUGH P. A. , BREGT A. K. , de HEUS M. J. , KLOOSTERMAN E. G.
Published: July 2006

The Flevopolders in the north‐west of The Netherlands are located on recently reclaimed, uniform, flat alluvial soils. Strong contrasts in soil were thought to be unlikely. Yet thermal imagery of experimental fields carried out over 4 years revealed the presence of a striped pattern with a regular wavelength of 24 m. This was remarkable considering that drainage had been carried out at a 12 m spacing. Crop yields, topographic heights, tensiometer data, penetrometer readings and soil profiles also indicated the presence of a 24m ‘wave’. Investigations into the land reclamation procedures carried out 20 years ago finally revealed the cause. The implications for management are discussed.
A comparison between the diffusivity of gases in soil cores and in soil aggregates
Authors: PRITCHARD D.T.
Published: July 2006

Gas diffusivity was measured in duplicate soil cores (10 cm long and 6 cm diameter) from depths of 0–10, 10–20 and 20–30 cm, and in beds of 1–2 mm aggregates taken from the same site at the same depths. A steady state method was used, with ethane as the diffusing gas. As the samples dried, the fractional air‐filled pore space increased, from 0. 1 to 0.45 for the cores and from 0.35 to 0.65 for the aggregates. The maximum relative diffusivity of the aggregate samples (0.38) was approximately twice that of the core samples, reflecting the difference in pore space. Equations are presented for calculating the solid, air and water fractions of the samples and for calculating the diffusivity within peds and aggregates. These calculations allowed a comparison of the diffusion/porosity relationship within aggregates and peds.
The distribution of native and labelled carbon between soil particle size fractions isolated from long‐term incubation experiments
Authors: CHRISTENSEN B. T. , SØRENSEN L. H.
Published: July 2006

Four soils with 6, 12, 23 and 46% clay were fractionated according to particle size after incubation for 5–6 years with 14C labelled straw, hemicellulose or glucose: 6–23% of the 14C was still present and the amount increased with increasing content of fine particles.

clay fractions contained 66–84% of the 14C and the silt fractions accounted for 4–19%. <2% was found in the sand fractions and 4–9% was water soluble. The distribution of the native C was: clay, 46–68%; silt, 20–31%; sand, 2–7%.

The clay fractions had higher relative proportions of 14C than of native C, the reverse being true for the silt fractions. This distribution pattern was not directly related to soil clay content or to kind of organic amendment.

The C enrichment factor of clay and silt fractions (per cent C in fraction/per cent C in whole soil) increased with decreasing fraction size for both native and 14C. However, clay enrichment factors were higher for 14C than for native C, whereas silt enrichment factors were lower.

A soil (9% clay) that had been incubated in the field for 18 years with 14C labelled straw was also analysed. Labelled C content at sampling was 9% of the initial value. In contrast to the other soils the distribution of labelled and native C was similar in the clay and silt fractions, which contained 55% and 33% of the whole soil C, respectively.

The results indicate that clay‐bound organic matter may be important in mediumterm organic matter turnover, whereas silt‐bound organic matter may participate in longer‐term organic matter cycling.
The solubility of cations in soils
Authors: BENIANS G.
Published: July 2006

Water‐soluble and exchangeable basic cations, and electrical conductivity, were measured in temperate and tropical soils. The ‘availability’ of cations in temperate soils is a function of both the amounts of exchangeable ions and the electrical conductivity of the solution, especially for divalent cations. In tropical soils the solubility of Ca and Mg seems less clear. The implications for some management problems are discussed.
Carbon/sesquioxide ratios in organic complexes and the transition albic‐spodic horizon
Authors: BUURMAN P.
Published: July 2006

Organic matter‐sesquioxide complexes in podzol B horizons are precipitated at specific carbon/sesquioxide ratios. Field data indicate that only part of the potential acidity is neutralized and that the maximum C/R2O2 ratio (minimum metal content) at which organic complexes will precipitate depends on pH of the soil and consequently on parent material and profile development. Although C/R2O3 ratios may be used regionally to predict the transition from soluble to precipitated complexes, such ratios cannot be used in soil classification or in a general definition of albic and spodic horizons.
Comparison of three field methods for measuring ammonia volatilization from urea granules broadcast on to pasture
Authors: BLACK A. S. , SHERLOCK R. R. , CAMERON K. C. , SMITH N. P. , GOH K. M.
Published: July 2006

Urea granules were broadcast on to pasture (Lolium perenne/Trifolium repens) at a rate of 100 kg N ha−1. The evolution of NH3 from the soil was measured using three methods: an enclosure system with continuous air flow (EM), an unconfined micrometeorological method (integrated horizontal flux method—IHFM) and by measuring the recovery of N as urea, NH4+ and NO3− (NRM). The cumulative loss after 96 h measured by the three methods was 24%, 25% and 30% of the N applied respectively. After 144 h the daily rate of loss was small. At this time, EM and IHFM estimated the loss at 28%, while the NRM estimated a 45% loss. The higher estimated loss by the NRM was attributed mainly to microbial immobilization of applied N.

Hourly fluxes estimated by the EM and the IHFM were very different. This was attributed to variations in the rate of urea hydrolysis which appeared to be more rapid in the confined EM system where the rate of soil drying was slower.
Annual losses of iron from moorland soils and their relation to free iron contents
Authors: GRIEVE IAN C.
Published: July 2006

The temporal pattern of iron loss from a moorland catchment was investigated by intensive stream water sampling. The total loss in 1 year was 2.11 kg ha−1 of Fe, with a pronounced autumn maximum. Iron concentrations in stream water were strongly correlated with dissolved organic matter content, but again with seasonal variation.

Free iron content measured on a number of soils in the catchment ranged from 3.1 to 8.7 kg m−2. Assuming soil development over 10 000 years, predicted loss of iron from the catchment is comparable in quantity to the amounts of free iron in the soils.
The effect of oxidation by periodate on soil carbohydrate derived from plants and microorganisms
Authors: CHESHIRE M. V. , SPARLING G. P. , MUNDIE C. M.
Published: July 2006

It has previously been shown that treatment of soil with periodate and tetraborate releases much of the carbohydrate and destroys an equivalent proportion of the soil aggregates. The residual carbohydrate is proportionately richer in glucose, arabinose and xylose, sugars characteristic of plant remains, than the whole soil.

The effect of sodium periodate (0.02 M, 6–168 h) and sodium tetraborate (0.1 M, 6 h) treatment of soil on carbohydrates of different origin was examined using 14C‐labelled soil in which the label was present in microbial products arising from 7 and 28 day incubations of 14C‐glucose in soil, or in both plant and microbial materials resulting from 12 week incubations of 14C‐labelled barley leaf and 1 year incubations of 14C‐labelled ryegrass in soil.

Arabinose and xylose were the sugars most resistant to periodate in the glucose incubated soil; in the ryegrass incubation arabinose, xylose and glucose were more persistent than galactose, mannose and rhamnose. In the barley leaf incubation arabinose was more persistent than galactose and rhamnose. Thus periodate oxidation did not distinguish between sugars of different origin in soil and it was concluded that in the case of arabinose and xylose the persistence related to differences in chemical structures rather than to physical factors such as particle size of the plant fragments.

The composition of the more stable residue can therefore not be used as an indication of polysaccharide origin in any comparison of the relative effects of plant and microbially derived material as aggregating agents.
Soil formation in the coast aeolianites and sands of Natal
Authors: MACVICAR C. N. , HUTSON J.L. , FITZPATRICK R. W.
Published: July 2006

The morphological, physical, chemical and mineralogical properties of eight prominent classes of soil developed in the coast aeolianites and sands of Natal are presented. These data and information on soil geography lead to the conclusion that: (i) losses of silica and bases and relative accumulation of iron (the ferrallitic process) have given rise to red and yellow kaolinitic materials; (ii) clay eluviation has given rise to coarse textured topsoils and to B2t horizons; and (iii) the hydromorphic process has caused grey colours in many sandy topsoils, plinthite development at some E/B horizon interfaces and gleying of some B2 horizons. In the soils on the older aeolianites, there is no evidence of either podzolization or the coarser textured topsoil being a younger geological deposit. The development of yellow soils in younger aeolianites may indicate a cooler climate than existed when red materials developed from the older aeolianites.
Incipient podzolization processes in Humic Acrisols of southern Spain
Authors: TORRENT J. , GOMEZ‐MARTIN F.
Published: July 2006

Soils with morphological evidence of podzolization occur in Sierra Morena (southern Spain). Six soils, identified as Humic Acrisols, were sampled for detailed study. Distribution of oxalate‐ and EDTA‐extractable Al in Fe in the profiles indicated that substantial amounts of both elements had been translocated from the A to the incipient podzolic B horizons. Part of the Al, but almost no Fe, was present as organic complexes, suggesting that these two elements were transported to, or remobilized in the B horizons by different mechanisms. Allophane was present, albeit in small amounts, in two soils. Both inorganic and organic theories of podzolization were able to explain the Fe and Al distribution data.
The dissolution and dispersion of dicalcium phosphate dihydrate in soils.
Authors: KIRK G. J. D. , NYE P. H.
Published: July 2006

The model described in part I is tested against concentration profiles of calcium, phosphate and pH measured in thin sections of a soil block in contact with a dissolving layer of DCPD. The soil parameters required by the model are also measured, and the major assumptions of the model discussed in view of the findings. The close agreement between the predicted and experimental profiles shows that all important processes have been accounted for in the model. These would have to be included in models of the dissolution of granular DCPD in soil.
Topographic controls of soil moisture distributions
Authors: BURT T. P. , BUTCHER D. P.
Published: July 2006

Soil moisture distributions on an instrumented hillslope at Slapton, South Devon, are compared to two topographic indices. The index a/s has been used in a computer runoff model to predict the location of zones of surface saturation on a hillslope (Beven & Kirkby, 1979), whilst the index plan curvature is derived from techniques of terrain analysis using gridded altitude data (Evans, 1980). Neither index is entirely satisfactory for predicting the changing pattern of soil moisture on the hillslope; a combined index proved most appropriate, but only at times of high soil wetness. The potential value of topographic indices as a basis for the prediction of soil moisture distributions and hillslope runoff is briefly discussed.
Effect of liming and air‐drying on the adsorption of phosphate by some acid soils
Authors: HAYNES R. J. , SWIFT R. S.
Published: July 2006

The effect of liming the A and B horizons of a number of acid soils on the subsequent adsorption of phosphate by soils retained moist or allowed to dry was investigated. Air‐drying increased the phosphate adsorption capacity but the reason was not clear.

When A horizons were maintained moist, incubation with lime for six weeks increased phosphate adsorption by four samples and had no effect on another. When A horizons were air‐dried, the effect was considerably reduced or reversed. For B horizons, which had considerably greater phosphate adsorption capacities than A horizons, liming decreased phosphate adsorption irrespective of whether the soils remained moist or were dried. The relative decrease in adsorption was, however, greater when the soils were dried.

In a more detailed study using one acid soil it was shown that incubation of the soil with lime for six weeks had no effect on phosphate adsorption by moist A and B horizons but after 36 weeks incubation liming decreased adsorption by the moist samples. If soils were dried then liming decreased phosphate adsorption after six or 36 weeks incubation. Such relative effects of liming on phosphate adsorption were confounded by the fact that air‐drying greatly increased the phosphate adsorption capacity of the unlimed soil. The drying effect was at least partially reversible following rewetting of the soil.

Results were interpreted in terms of the lime‐induced increase in soil pH causing (i) the surface charge conferred on soil oxide surfaces to become more negative (thus decreasing phosphate adsorption) and (ii) the precipitation of exchangeable Al as hydroxy‐Al polymers resulting in the formation of new, highly active, adsorbing surfaces (thus increasing phosphate adsorption). Phosphate adsorption by moist limed soils can, therefore, be increased, decreased or unaffected depending on the relative magnitudes of these two processes. It is suggested that after liming, and/or air‐drying, crystallization of amorphous materials progressively decreases their surface area and adsorbing capacity. Thus, liming tends to decrease phosphate adsorption when the soils are dried.
Iron oxides in two Oxisols from the Brazilian coastal plain
Authors: FABRIS J. D. , RESENDE M. , DA SILVA E. GALVAO , COEY J. M. D.
Published: July 2006

Two Oxisols from the B2 horizon at similar locations 2 km apart on the Brazilian coastal plain with a udic, isohyperthermic regime were practically identical in chemical composition but differed markedly in colour; one was a dark reddish brown, the other a pale ochre. Mossbauer spectra at 295 K, 80 K and 4.2 K indicated a clear difference in iron oxide mineralogy. Iron was present as aluminous hematite and goethite, with Al substitutions of approximately 20% in the two phases. However, the relative proportion of iron present in hematite and goethite was 45:55 in the first sample and 12:88 in the second. Possible reasons for these differences are discussed.