bluuebunny/crossref_metadata_2025 huggingface dataset:
A lysimeter study of the fate of nitrogen applied to perennial ryegrass swards: soil analyses and the final balance sheet
Authors: WEBSTER C. P. , DOWDELL R. J.
Published: July 2006

Labelled fertilizer nitrogen was applied at a rate of 40 g N m−2 to grass swards growing in lysimeters containing monoliths of a sandy loam soil. After 5–7 years, during which time crop uptake and drainage losses of tracer nitrogen were measured, the soils were analysed to quantify the labelled nitrogen remaining. Approximately one‐third (range 31–35%) of the applied labelled nitrogen remained, with over 70% of this residue located in the top 20 cm of soil. The rate of mineralization of immobilized tracer nitrogen declined exponentially; after four years the release rate was almost constant, and was equivalent to 2% of the residual labelled nitrogen. Total labelled nitrogen measured in crop, drainage and soil amounted to 93–98%. That unaccounted for was presumed lost by denitrification, largely in the form of dinitrogen, as measured rates of nitrous oxide emission were negligible. The recovery was greatest (and by implication, the gaseous loss smallest) when fertilizer was applied in 1975 during a particularly warm and dry summer.
Compaction of a swelling clay soil by agricultural traffic; effects upon conditions for growth of winter cereals and evidence for some recovery of structure
Authors: BLACKWELL P. S. , WARD M. A. , LEFEVRE R. N. , COWAN D. J.
Published: July 2006

A swelling stagnogley soil remained unwheeled or was uniformly wheeled by a combine harvester and a tractor in two successive autumns before direct drilling winter cereals. Combine wheeling of the soil at its wettest condition caused the largest loss of soil porosity.

The autumn and spring of the second growing season for the winter cereals were wetter than long term average. The smaller porosity in the wheeled soil, created lower soil redox potential and smaller oxygen flux as well as greater soil strength and larger amounts of available water, but little difference in soil temperature. The crop in the wheeled soil had fewer plants, less root and a lighter yield than in the unwheeled soil.

The wheeled soil recovered some porosity and lost strength after wetting and drying during the second growing season, whereas soil freezing had very little effect. This restructuring was sufficient to reverse some of the detrimental effects of compacting the soil.
A model of ammonia volatilization from applied urea. I. Development of the model
Authors: RACHHPAL‐SINGH  , NYE P. H.
Published: July 2006

Urea application to soil raises the pH and ammonium concentration, thus providing ideal conditions for ammonia volatilization. A mechanistic model is presented, which combines the process of ammonia volatilization with the simultaneous transformation and movement of urea and its products in soil, for predicting the concentration profiles of urea, ammoniacal‐nitrogen and soil pH, and ammonia losses, following application of urea.

The model consists of continuity equations describing the diffusion and reaction of urea, ammoniacal‐nitrogen and soil base; it takes into account the volatilization of ammonia and the concurrent acidification of the soil surface; and considers a variable PCo2 profile due to soil respiration and urea hydrolysis. The derivation of the continuity equations and their boundary conditions, calculations of ammonia volatilization, and appropriate methods for numerical solutions are described.
A model of ammonia volatilization from applied urea. II. Experimental testing
Authors: RACHHPAL‐SINGH  , NYE P. H.
Published: July 2006

Experimental methods for the measurement of the transfer coefficient for ammonia volatilization from the soil surface to the atmosphere, the gaseous diffusion impedance factor in soil, and other parameters required by the predictive model are described. Following surface application of urea to soil columns, the measured concentration profiles of urea, ammoniacal‐nitrogen and soil pH, and the losses of ammonia by volatilization, were compared with the model predictions. The very good agreement between the measured and the predicted results suggested that all important processes have been accounted for in the model.
On the limitations of the simplified Elovich equation in describing the kinetics of phosphate sorption and release from soils
Authors: POLYZOPOULOS N. A. , KERAMIDAS V. Z. , PAVLATOU ATHENA
Published: July 2006

The kinetics of phosphate sorption and release from soils are often described by a simplified form of the Elovich equation. However, examination of data obtained with three soils from Greece as well as of published data, based on a modified version of the Elovich equation, showed that the assumptions underlying derivation of the simplified form are not valid in all cases. This modified version is free from any a priori assumptions, describes the kinetics of phosphate reactions with soils in a realistic manner and points out to the existence of more than one stage in the process.
Profile characteristics, and form and surface activity of inorganic phosphorus in a deep red Kenya coffee soil (Nitosol)
Authors: KETER J. K. A. , AHN PETER M.
Published: July 2006

The paper examines some of the physical and chemical properties of a deep red friable clay profile (Nitosol) developed in the Kenya highlands over trachyte. This soil is widely planted to coffee. The profile is remarkable for the depth and uniformity of the B horizon and for its stable microaggregation. Despite a clay content of 50–60% throughout the deep solum, the soil feels and handles like a loam.

Work with radioactive phosphorus on samples from the profile and from nearby experimental plots under coffee showed that the activity, and the amounts, of surface phosphate fractions decreased in the order Fe‐P, Al‐P and Ca‐P, but the order of decrease of specific surface activity was Al‐P, Fe‐P, Ca‐P. The relative availabilities of these forms is discussed.
Cadmium accumulation in soils from long‐continued applications of superphosphate
Authors: ROTHBAUM H. P. , GOGUEL R. L. , JOHNSTON A. E. , MATTINGLY G. E. G.
Published: July 2006

A simple, sensitive method developed for the analysis of geostandards was used to measure the accumulation of Cd in soils from superphosphate applied annually to grass‐land and arable soils for many years. Rates of application were equivalent to 33 kg P and 5 g Cd ha−1 yr−1 for 95 yr in three experiments in England and to 37 kg P and 20 g Cd ha−1 yr −1 for 30 yr in one experiment in New Zealand. Very little Cd accumulated in the surface horizons (0–22.5cm) of either of the arable soils from England; about one‐quarter of the applied Cd was detected in the sub‐soil (22.5–45.0 cm) of one experiment (Broadbalk) but none in the second (Barnfield). About one‐half of the applied Cd was retained in the 0–22.5 cm horizon of grassland soils from both England and New Zealand. The light (<2.2 gcm−3) organic‐rich fraction of Park Grass soil from Éngland contained about three times as much Cd as the heavier, mineral‐rich fraction. This suggests that when Cd is incorporated into organic matter its mobility is decreased and soil pH then has smaller effects on its mobility. Uptake of Cd by grass‐clover pasture in New Zealand averaged only 0.4 g Cd ha−1 yr−1 or 2% of the amount applied.
A comparison of measured and theoretical soil acidity diffusion coefficients over a wide range of pH
Authors: NYE P. H. , AMELOKO A.
Published: July 2006

The soil acidity diffusion coefficients have been measured at two Pco2 levels with values in the range 2–70 × 10−9 cm2 s−1. The coefficient passed through an ill‐defined minimum in the pH range 5–6.5. Theoretical values, calculated on the basis that the only significant acid‐base carriers in the soil were the H3O+ ‐H2O and H2CO3‐HCO−3 pairs, agreed well with the experimental values over the whole pH range at Pco2= 0.005 atm. Agreement was not so good however at a CO2 pressure of 0.0003 atm., especially in the neutralalkaline pH range. This was thought to be due to difficulties in maintaining this level of CO2 throughout the soil samples.
Competitive adsorption of humus acids and phosphate on goethite, gibbsite and two tropical soils
Authors: SIBANDA H. M. , YOUNG S. D.
Published: July 2006

Competition in adsorption between humic acid (HA) or fulvic acid (FA) and phosphate on synthetic goethite, gibbsite and two tropical soils was studied. The results for both goethite and gibbsite showed that HA and FA competed strongly with phosphate for adsorption sites at low pH values. The soils showed a similar result with a reduction in phosphate adsorption resulting from the addition of HA at the pH of the soils. The competition between HA and phosphate at different pH levels is illustrated by comparing the adsorption envelopes for phosphate on goethite, gibbsite and the two soils in the presence and absence of HA. The trends observed may be explained by the relative positions of the maximum buffer‐power (buffer capacity) of the organic acids and of phosphoric acid which are shown to lie in different pH ranges.
Forms of aluminium in some acid permanent grassland soils
Authors: JARVIS S. C.
Published: July 2006

The more labile forms of aluminium in a range of soils from areas of permanent grassland were determined with a number of selective extractants. The amounts of exchangeable A1 extracted with molar KCl were dependent upon pH, while the amounts exchangeable with 0.3 M LaCl3, although much greater, were not well correlated with pH. There were good correlations between soil organic C content and A1 extracted by (i) 0.5 M EDTA and (ii) 0.1 M potassium pyrophosphate. Pyrophosphate extracted greater amounts than any of the other extractants (sodium citrate/dithionite, ammonium oxalate (dark), acid oxalate (UV radiation), as well as those already mentioned). It was concluded that much of the extractable A1 in soils was associated with organic matter. Addition of lime to one of the soils reduced the amount of A1 extracted by all reagents except dithionite and acid oxalate solutions. There were considerable differences between soils in their release of A1 to continuous leaching with 0.01 M CaCl2. Despite these differences between the soils in organically bound extractable Al, the differences in the amounts and patterns of release of A1 with CaCl2did not appear to be related to organic matter contents, nor to the other determined properties.
The forms of cobalt in some Scottish soils as determined by extraction and isotopic exchange
Authors: McLAREN R. G. , LAWSON D. M. , SWIFT S.
Published: July 2006

The results of fractionation and correlation studies provided evidence that cobalt in soils is associated predominantly with the soil oxide fraction, particularly the manganese oxides. Only a small proportion of the total cobalt present in soils was extracted by acetic acid, EDTA, pyrophosphate or hydroxylamine. Cobalt extracted with these reagents was considered to be derived principally from easily reducible manganese oxides, although the origin of the cobalt extracted by acetic acid in particular was not well defined. The bulk of the cobalt present in soils appeared to be occluded by more highly crystalline oxide materials or was present in the structures of primary and secondary minerals.

Labile cobalt in soil was assessed by extraction with acetic acid and EDTA and by determination of isotopically exchangeable cobalt. The amounts of cobalt extracted by both EDTA and acetic acid were highly dependent on the length of extraction period and on the temperature of extraction. Neither of these reagents appeared likely to give good estimates of the quantity or intensity factors of soil cobalt supply to plants as defined by the isotopic exchange determinations.
Anisotropic shrinkage of clay cores, and the interpretation of field observations of vertical soil movement
Authors: TOWNER G. D.
Published: July 2006

An anisotropic state was induced in saturated clay cores by unidirectional compression. The cores were allowed to dry slowly in the laboratory and the resulting linear shrinkage was measured in all three dimensions. The rate of shrinkage was less in the precom‐pressed direction than in the other directions. An analysis is given for characterizing the anisotropic shrinkage.

An analysis is made of the vertical soil movement occurring in response to wetting or drying within the profile in which volume changes are anisotropic. It is shown that for saturated clays the ratio of added water (expressed as a depth) to the vertical soil displacement is greater than or equal to unity, though it is unlikely to exceed 5. When the soil volume properties are isotropic, the ratio has one of two integer values: 1 when the soil is constrained to move only vertically, and 3 when it is free to change volume in three dimensions. The measured value should be used for modelling changes in crack geometry.
The self‐diffusion of sodium in soil: factors affecting the surface mobility
Authors: STAUTON S.
Published: July 2006

A study is presented of the self‐diffusion of sodium in a sub‐soil. Impedance factors (fs)associated with the surface phase have been derived, representing the mobility of sorbed sodium ions relative to mobility in an ideal solution. Effects of drying, of cationic com‐position and of enrichment with either native clay fraction or ‘pure’ clay minerals were investigated. The liquid phase impedance factor (fL) without added clay was 0.29: clay enrichment affected soil structure and hence fL. Values of fs were in the range 0.19–0.05, and were about one‐third of fL. The value off, decreased as clay content increased, being halved when 50% native clay or 10% clay mineral was added. In a sodium saturated soil fs was 0.06, less than half that in a calcium saturated soil.
Water and oxygen regimes under conifer plantations and native vegetation on upland peaty gley soil and deep peat soils
Authors: KING J. A. , SMITH K. A. , PYATT D. G.
Published: July 2006

Concentrations of oxygen and carbon dioxide were measured in an upland peaty gley soil during two growing seasons and a deep peat during one season. Measurements were compared with the soil water regimes on both soils. Comparison was also made between planted areas of Sitka spruce and Lodgepole pine, and areas of the native vegetation (Molinia grassland on the peaty gley, and Calluna heath on the deep peat). In 13 m tall pure stands of the pine and spruce on the peaty gley soil about 28% of the rainfall was intercepted by the canopy and evaporated without reaching the soil, and the watertable was deeper and matric potentials were lower than under grass. When the matric potential fell below −5 kPa in the upper soil layers, high oxygen concentrations prevailed. In undisturbed peat, waterlogged conditions produced an anaerobic regime virtually to the surface, but a 1 m deep drainage ditch lowered the watertable and created an aerobic regime within the top 0.3 m of peat. The presence of tree crops on drained plots increased the depth of drying during the summer months, and aerobic conditions reached 0.4 m depth under Sitka spruce and 0.5m under Lodgepole pine. On the peaty gley also, Lodgepole pine dried and aerated the soil to a greater depth than Sitka spruce during the summer, but no difference in water regime was evident in the winter.
Use of the Kubelka—Munk theory to study the influence of iron oxides on soil colour
Authors: BARRON V. , TORRENT J.
Published: July 2006

The Kubelka–Munk theory, which is commonly applied to ‘pigment mixtures’, adequately predicted the colour of mixtures of synthetic haematite, synthetic goethite and deferrated soil powders. The theory illustrated the higher pigmenting effect of haematite compared with goethite. In mixtures containing haematite the calculated colour coordinates could be combined into simple ‘redness’ indices that were highly correlated with haematite content and were not appreciably influenced by goethite.

The theory was also applied to the study of the chromatic characteristics of 98 soils, differing widely in their origin but having an organic matter content <2% in which haematite or goethite was the dominant Fe oxide. The theory showed that the average ‘soil’ haematite and ‘soil’ goethite had colours similar to those of their synthetic counter‐parts, whereas the rest of the soil components could be considered as an essentially ‘grey’ matrix. It was also useful in predicting the haematite and goethite contents of soils either from several reflectance measurements of soil‐white standard mixtures or from the indices of redness developed for the synthetic mixtures.
A simple model for predicting the rates of dissolution of sparingly soluble calcium phosphates in soil
Authors: KIRK G. J. D. , NYE P. H.
Published: July 2006

The effect of non‐uniform distribution of particles in the soil on the rate of dissolution of calcium phosphate particles was investigated, using a negative binomial distribution to describe the degree of clumping of the particles. A randomly distributed sample dissolved about 10% more slowly than a regularly distributed one. For a degree of clumping in which the sum of the spherical volumes influenced by particles was about 10% of the whole soil volume, the predicted rate of dissolution was reduced by about 85%. The effect of a range of particle sizes in the applied material was also investigated. Typical grades of commercial rock phosphate contain a high proportion of fine particles, resulting in a rapid initial rate of dissolution of the applied material, but the rate trails off as the small particles are exhausted.

The effect of the presence of plant roots was also considered, using average root characteristics and assuming the root effects to be spread over the whole soil volume. The rate of calcium phosphate dissolution was increased by root uptake of dissolved phosphate ions, by an amount depending on the rooting density and the rate of calcium phosphate application, and by secretion of acid by the roots. In many circumstances where rock phosphates are applied as fertilizers, plants are likely to be rhizosphere acidifiers; sufficient acid may be secreted to render rock phosphates soluble where they would other‐wise be insoluble. Generally, calcium uptake will not greatly affect the rate of calcium phosphate dissolution.
The fractionation of soil polysaccharide by electrofocusing
Authors: CHESHIRE M. V. , MUNDIE C. M.
Published: July 2006

Soil polysaccharide isolated from alkali extracts of Countesswells and Insch series soils has been submitted to electrofocusing with ampholyte in dextran gel. To aid detection, polysaccharide which had been dyed with either Procion Red or fluorescein or labelled 14C by prior incubation of the soil with 14C‐labelled substrates, was also used.

After electrofocusing, polysaccharide was distributed in the gel over the entire range of pH used, 1.9–10, with the greatest concentration occurring within the pH 1.9–4 region. The distribution was partly the result of adsorption and diffusion. Re‐electrofocusing of material isolated from particular regions of the bed located most of it in the original position, although considerable dispersion occurred, particularly with the less strongly charged material and there was evidence for association/dissociation reactions. This was also observed in a medium containing 8 M urea.

The proportion of uronic acid was greatest in the polysaccharides fractions from the pH 3.0–4.0 region of the bed. The increased acidity of the fraction nearest to the anode appeared to relate to the presence of other organic acids, such as succinic, fumaric and levulinic acids. No difference could be detected between the separation of polysaccharide from the two different soils or between the labelled polysaccharides derived from an incubation of 14C‐glucose with soil and those from an incubation of 14C‐plant material.
Effects of season and management on the vane shear strength of a clay topsoil
Authors: DOUGLAS J. T.
Published: July 2006

Vane shear strength, water status and bulk density were measured at various times in a growing season at two depths in a swelling clay topsoil. The site comprised experimental plots that had been ploughed annually, or direct‐drilled for 10 years; short‐term fallow areas, created on adjacent long‐term grassland, were compared with the arable plots. In the middle of the topsoil layer (nominally 120 mm depth) of all three treatments shear strength was linearly related to water content, and similarly to bulk density in the direct‐drilled and ploughed soils. Closer to the soil surface (nominally 40 mm), relationships between strength and wetness or density were less distinct, particularly in the spring, when drying was not accompanied by an increase in strength; possible reasons for this anomaly are considered. The shear strength of the untilled soils was greater, at both depths, than that of the ploughed soil. Other factors including density, water potential, soil structure and organic constituents, differed with time or between treatments, and their contribution to variations in shear strength are discussed.
The preparation of soil thin sections for biological studies
Authors: TIPPKÖTTER R. , RITZ K. , DARBYSHIRE J. F.
Published: July 2006

A method is described that permits the preparation of soil thin sections up to 6 × 8 cm in approximately 14 days without any discernable artefact. Soil samples are fixed in buffered glutaraldehyde, dehydrated rapidly in a graded series of acetone: water mixtures and impregnated with a polyester resin. The method effectively preserves biological material, such as delicate protozoan cells and root tissues. A range of stains were tested for staining roots in soil blocks and in soil thin sections.
Interaction forces between soil particles: shear moduli of the < 2 μm size fraction
Authors: PIPER J.
Published: July 2006

The shear moduli of the < 2 μm size fraction of three soils have been measured for samples of 10–35% w/w solid. Samples were thixotropic, the shear modulus increasing with time. This increase can be described by simple models and visualized in terms of the formation of links between particles. For a given soil the shear modulus increases with ionic form in the order Ca2+∼Mg2+ <K+ <Na+ < Li+ and varies in a complex manner with electrolyte concentration.
Adsorption of sulphate and fluoride by variable charge soils
Authors: ZHANG G. Y. , ZHANG X. N. , YU T. R.
Published: July 2006

The adsorption of sulphate and fluoride by three variable charge soils was studied. Adsorption increased with increase in the amount of sulphate added at constant pH, and decreased with increase of pH.

The ratios of the amount of released OH−to that of the adsorbed SO2‐4 at pH 5–0 were 0.12, 0.14 and 0.20 for the three soils, respectively, much lower than the corresponding OH−/F− ratios which ranged from 0.3 to 1.0. For a ferric acrisol the OH− released accounted, on average, for only 15% of the SO2‐4 adsorbed, leaving more than 60% to be explained by the decrease in positive charge and the increase in negative charge carried by the soil.
The solution chemistry of podzolic soils from the eastern Canadian shield: a thermodynamic interpretation of the mineral phases controlling soluble Al3+andH4SiO4
Authors: MANLEY E. P. , CHESWORTH W. , EVANS L. J.
Published: July 2006

Thirty‐one soil solutions were extracted by immiscible displacement with CCl4 under high speed centrifugation from sub‐horizons of three podzolic soils from north‐eastern Ontario, Canada. The solutions were analysed for major cations and anions and a speciation of dissolved Fe and Al was attempted to distinguish ‘free’, ‘organically bound’ and ‘inorganically bound’ species. Results indicated that the Ae (E) horizon solutions were of low pH and contained mainly organically bound Fe and Al. With depth, pHs increased, ionic strengths decreased and the relative proportion of inorganically bound Fe and Al increased. Although application of phase diagrams permitted only a semi‐quantitative interpretation of the data, all horizon solutions, with the exception of some Ae solutions, appeared supersaturated with respect to likely occurring crystalline and amorphous aluminosilicates [kaolinite, halloysite, allophane (Al:Si=l) and imogolite]. Of the phases considered, reactions involving imogolite‐allophane, gibbsite‐halloysite, gibbsite‐allophane and gibbsite‐imogolite all appeared reasonable in controlling the content of Al3+ and H4SiO4 in solution, although the presence of gibbsite and imogolite could not be definitely confirmed in these soils.
Plant uptake of exchangeable and non‐exchangeable potassium. II. Influence of soil type on uptake by onion roots
Authors: MITSIOS I. K. , ROWELL D. L.
Published: July 2006

Measurements and predictions of uptake of non‐exchangeable K have been made for three soils. Exchangeable K is important in controlling the extent to which non‐exchangeable K is used; rate of diffusion of exchangeable K seems less important. Rate of release of non‐exchangeable K did not vary much between soils, but critical release concentrations in solution varied from 33 to 85 μM with little obvious effect on the extent of use of non‐exchangeable K.
Composition and properties of poorly ordered minerals in Welsh soils. II. Phosphate adsorption and reactivity towards NaF solution
Authors: ADAMS W. A. , GAFOOR S. N. , KARIM M. I.
Published: July 2006

Eleven horizons of acidic soils developed from Lower Palaeozoic sedimentary rocks in mid Wales contained varying amounts of poorly ordered minerals. In nine of these over 70% of the phosphate adsorption capacity was attributed to poorly ordered minerals. Iron oxide with substituted Al, and a separate Al oxide, together accounted for the phosphate adsorption of the poorly ordered fraction. Aluminium‐substitution had no major effect on the adsorption capacity of Fe oxide, but since Al occurred in both active minerals it masked the effect of Fe on phosphate adsorption in simple correlations. The relative contribution of the two mineral forms to phosphate adsorption varied widely between soils. Aluminium as a substituent in Fe oxide and in ‘free’ oxide form was responsible for the soils’ reactivity towards NaF, but no distinction could be made between these poorly ordered forms. For certain horizons both poorly ordered Al and Si were correlated with OH− release, but Al oxides were more important than silicates.
The effect of the frequency of sampling on the observed concentration of oxygen in an afforested peat soil
Authors: RAY D. , PYATT D. G. , WHITE I. M. S.
Published: July 2006

Samples of air or water were extracted daily from porous pots buried within the rooting zone of trees planted on a deep peat soil. For most pots, the O2 concentration in the fluid increased with the number of samples taken each day, presumably because air was drawn into the pot from shallower depths. Sampling frequency should therefore be chosen as a compromise between the needs to increase precision and to minimize introduced bias.
Weathering of a mica introduced into four acidic forest soils
Authors: HATTON A. , RANGER J. , ROBERT M. , NYS C. , BONNAUD P.
Published: July 2006

A mica was inserted into the soil at four sites to try to identify, in situ, the physico‐chemical changes in the soil caused by the introduction of different tree species, and especially conifers. Changes in the chemistry and mineralogy of the mixed‐layered mica, mica‐chlorite, vermiculite, after 1 1/2 and 31/2 years in the soil, showed good differentiation between soil horizons and between soil types. Differences due to tree species were present, but small. The mechanisms of mineral evolution can be defined with reference to experimental data obtained in the laboratory. In litter layers, the mica‐chlorite sheet was transformed into a mica‐vermiculite, and exchangeable cations predominated on the exchange sites. In the organo‐mineral horizons, changes varied depending on the soil type: in the podzol, transformation was similar to that in the litter layers, but in the sol brun acide, changes were dominated by the Al fixation on the exchange sites and its rapid hydroxylation which blocks these sites, leading to the formation of Al intergrade minerals.

Different tree species produced deviations linked to their ability to cycle cations, and also to the different organic materials produced which can attack the mineral.

The method has the potential to define the present soil environment and weathering processes, but it needs a more complete experimental design and the use of statistics to clarify the effects of the parameters and their interactions.
A constant potential titration method for studying the kinetics of Cu2+ desorption from soil and clay minerals
Authors: JOPONY M. , YOUNG S. D.
Published: July 2006

The kinetics of Cu2+ desorption from a contaminated Malaysian padi soil, English Supreme kaolinite and Wyoming bentonite are studied using a constant potential titration method. This technique involves maintaining a constant Cu2+‐sensitive electrode potential corresponding to a Cu2+ ion activity below that which would naturally be supported by the soil in suspension. This is achieved by the controlled addition of complexing agent. Desorption occurs in response to the artificially reduced solution activity and the rate of the desorption reaction is revealed by the rate of addition of the complexing agent.

The desorption results were fitted to three established kinetic equations, all of which showed reasonable agreement with the data. In particular, a two‐constant rate equation demonstrated some consistency between different materials. Both first‐order and ‘diffusion’ kinetic equations appeared to apply within specific titration conditions. Each equation is discussed in terms of its implied desorption mechanism and the inconclusive nature of such mechanisms for short term (< 1 hour) desorption reactions is illustrated.
The fate at several time intervals of 15N‐labelled ammonium nitrate applied to an established grass sward
Authors: BRISTOW A. W. , RYDEN J. C. , WHITEHEAD D. C.
Published: July 2006

15N‐labelled ammonium nitrate solution was applied in late April to circular, enclosed micro‐plots prepared by pressing open‐ended polypropylene cylinders into an established sward of perennial ryegrass. Cylinders were removed from the ground at intervals between 2 and 370 days after the application and assessments made of the distribution of 15N in plant and soil components. Of the added labelled N, 54.7% was recovered in the herbage which was cut four times during the growing season and again at the final sampling date. After two days, 37% of the labelled N was recovered in the soil microbial biomass. Large fluctuations occurred in the amount of 15N recovered in the soil microbial biomass over the next 14 days suggesting that rapid cycling of 15N occurred between this fraction and the mineral N fraction. After the first cut in late May, translocation of15N occurred more slowly from the roots into the stubble than from stubble into new herbage, so that the amount in the stubble declined more rapidly than did that in the roots. During the winter, there was no net transfer of N from the roots to above‐ground components of the sward. By the end of the growing season, half the 15N remaining in the sward was immobilized in the humified fraction of the soil organic matter; some of this was mineralized in the following spring.
Concentration of phosphorus and sulphur at soil ped surfaces
Authors: QURESHI R. H. , JENKINS D. A.
Published: July 2006

Pedogenesis involves reorganization of a soil's components and thus relocation of nutrients within the microfabric. This has particular relevance to P which, being relatively immobile, is needed within the immediate root environment. The spatial distribution of P and S in four profiles (haplaquepts, eutrochrept, ochraqalf) with well developed prismatic structure has been investigated at the 1 mm scale, by physical sampling of successive ped surface zones, and at the 1 μm scale by electron probe microanalysis. Results reveal distinct though variable patterns of concentration of P and S at ped surfaces (0.1–3 mm depth) in certain profile horizons; correlation with extractable Ca, Al & Fe proved obscure by macroanalysis, but microanalysis showed specific associations variously interpreted as detrital grains (apatite, monazite, etc.), organic debris or adsorbed phosphate. Such heterogeneity in distribution is mostly consistent with the microfabric seen in thin‐section, although some remains cryptic. This is important since plant roots selectively sample the differentiated ped surfaces and not the bulk homogenized soil analysed in the routine assessment of nutrient availability.
Design of a database for Scottish soils
Authors: BROWN K. W. M. , GAULD J. H. , SMITH B. F. L. , BAIN D. C. , BURRIDGE J. C. , INKSON R. H. E.
Published: July 2006

The factors involved in the design and structure of a database for Scottish soils are described. Codes were extensively used for data entry, which though restrictive, minimized entry errors, reduced file space and make subsequent statistical analysis easier. The database contains records of soil profile descriptions, systematic chemical and physical analyses for all profiles sampled, as well as mineralogical and spectrochemical trace element analyses for a limited number of selected soils. Query and report writer facilities are described and were used for the production of reports, tables and maps.
Causes of crop patterns in eastern England
Authors: EVANS R. , CATT J. A.
Published: July 2006

Growth and yield of cereals were measured at four sites in eastern England where crop patterns have been repeatedly observed on aerial photographs. The patterns were related to archaeological features, infilled river channels, interbedding of lithologically diverse pre‐Quaternary sediments, periglacial disturbance of shallow loamy soil over Chalk, and the occurrence of minor valleys incised into chalky till. They resulted from differential germination and growth rates, which were in turn related to differences in (a) available water in the soil, (b) the inhibition of root extension by hard chalk, (c) soil temperature and (d) the workability of soils during drilling of spring‐sown crops. Yield losses resulting from the patterns ranged from 15 to 51 %.
Predicting the rate of dissolution of lime in soil
Authors: NYE P. H. , AMELOKO A. Y.
Published: July 2006

A disc of CaCO3 was brought into contact with a column of moist acid soil, incubated for 6 days, the soil cut into thin sections, and the pH measured. The pH profile suggested that the rate of dissolution was controlled by the rate of acid‐base diffusion in the soil near the interface of the soil and the CaCO3 disc.

A mechanistic model was developed, containing no arbitrary assumptions or fitting parameters, to predict the rate of neutralization of acid soil by CaCO3 particles of different size grades and at different application rates. The course of neutralization of soil at pH 3.0 and 4.9 with fine, medium and coarse grades of CaCO3 was measured and compared with the model predictions. The agreement was satisfactory within the limits imposed by experimental difficulties.
Distribution of 14C between particle size fractions and carbohydrates separated from a peat incubated with 14C‐glycine
Authors: WILLIAMS B. L. , CHESHIRE M. V. , SPARLING G. P.
Published: July 2006

Samples of fresh Sphagnum peat from a raised bog were amended with 14C‐labelled glycine. The distribution of 14C between particle size fractions obtained by wet sieving (sieve sizes 1, 0.5, 0.25, 0.15 and 0.05mm) was determined immediately on control (unincubated) samples and after 1, 6 and 12 months incubation at 10°C. The recovery of glycine in solution was almost 100%. During the incubation with 14C‐glycine, 14CO2 was released within the first 20 weeks, equivalent to 51.5% of the added 14C, but thereafter very little 14CO2 was evolved. After 26 weeks a substantial amount of 14C was distributed amongst all the fractions, but the greatest incorporation (4.47%) occurred in the finest fraction (0.005–0.05 mm). Labelling of the other particle size fractions was <2.3% of added 14C. Carbohydrate accounted for 23% of 14C in the finest fraction and the sugars, rhamnose, arabinose, xylose, mannose, galactose and glucose all became labelled. Rhamnose showed the greatest, and arabinose, galactose and xylose the least, increase in specific activity; glucose and mannose had intermediate values. It was concluded that the finest fraction in peat contains a significant proportion of the microbially‐synthesized material.
The importance of exchangeable cations and resin‐sink characteristics in the release of soil phosphorus
Authors: CURTIN D. , SYERS J. K. , SMILLIE G. W.
Published: July 2006

The significance of exchangeable cations in the release of phosphorus by sequential extraction with water was evaluated in 11 acid (pH 5.0–6.3) New Zealand soils contrasting in P status and P retention. The release of P from Na‐saturated soil exceeded that from the original Ca‐dominated soils by up to four‐fold. Possible explanations for the larger P release in the Na system include: (i) desorption of P induced by increased surface negative potential associated with the exchange of Na for Ca/Mg, and/or (ii) accelerated dissolution of Ca phosphate compounds or complexes resulting from the creation of a sink for Ca.

The potential of a series of anion‐ and cation‐exchange resin systems (AER and CER, respectively) as sinks for labile soil P was also examined. For all soils studied, P extracted by AER‐HCO3 <AER‐OH/CER‐Na< AER‐OH/CER‐H. The success of the AER‐OH/ CER‐H system in extracting P is attributed to its ability to remove exchangeable Ca and Mg, and to reduce the ionic strength of the equilibrating solution. A high correlation (r= 0.99**) was obtained between P extracted by AER‐HCO3 and that removed by sequential extraction with water. Also, the amounts of P extracted by AER‐OH/CER‐H and NaCl/ H2O were closely correlated (r= 0.95**), suggesting similar release mechanisms. The results obtained indicate that charge‐balancing cations, particularly Ca which is the predominant exchangeable cation in the majority of soils, exerts a more significant control on soil P equilibria in acid soils than is commonly recognized.
Total and extractable trace element contents of soils in England and Wales
Authors: ARCHER F. C. , HODGSON I. H.
Published: July 2006

Soil samples taken by soil auger to a depth of 150 mm from randomly selected agricultural fields throughout England and Wales were analysed for total As, B, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se and Zn, acetic acid‐extractable Cd, Co, Cu, Ni, Pb and Zn, EDTA‐extractable Cd, Co, Cu, Ni, Pb, Se and Zn, ammonium oxalate extractable Ni and Mo and hot water‐extractable B. Median, log‐derived mean and range data are given for each element. Median values are given also by parent material and textural grouping.
Effect of water content on the fabric of a soil material: an experimental approach
Authors: BRUAND A. , PROST R.
Published: July 2006

To characterize the fabric of a wet soil sample two sets of experiments were performed. In one, water retention and shrinkage curves were determined with samples stored at the field water content, and in the other, pore size distribution curves and microscopic observations were made as samples progressively dried. The experiments were performed with soil samples of different aggregate sizes to determine the contribution of each class of pores to porosity.

Data were analysed by comparing (i) the amount of water extracted from the sample, (ii) the air‐filled porosity of the sample and (iii) the accumulated pore volume by mercury injection, each in relation to the equivalent pore radius. This gives information on the geometry of pores developed during the drying process. It has shown that micrometric cracks in dried soils are not artefacts but the result of a more severe drying never reached by the material in the field.
Denitrification in drained and undrained arable clay soil
Authors: COLBOURN P. , HARPER I. W.
Published: July 2006

Emissions of nitrous oxide (N2O) and nitrogen gas (N2) from denitrification were measured using the acetylene inhibition method on drained and undrained clay soil during November 1980‐June 1981. Drainage limited denitrification to about 65% of losses from undrained soil. Emissions from the undrained soil were in the range 1 to 12 g N ha–1 h–1 while those from the drained soil ranged from 0.5 to 6 g N ha–1 h–1 giving estimated total losses (N2O + N2) of 14 and 9 kgN ha–1.

Drainage also changed the fraction of nitrous oxide in the total denitrification product. During December, emissions from the drained soil (1.8±0.6 gN ha–1 h–1) were composed entirely of nitrous oxide, but losses from the undrained soil (2.7 ± 1.1 g N ha–1 h–1) were almost entirely in the form of nitrogen gas (the fraction of N2O in the total loss was 0.02). In February denitrification declined in colder conditions and the emission of nitrous oxide from drained soil declined relative to nitrogen gas so that the fraction of N2O was 0.03 on both drainage treatments. The delayed onset of N2O reduction in the drained soil was related to oxygen and nitrate concentrations. Fertilizer applications in the spring gave rise to maximum rates of emission (5–12g N ha–1 h–1) with the balance shifting towards nitrous oxide production, so that the fraction of N2O was 0.2–0.8 in April and May.
The reactions of cadmium with calcium carbonate surfaces
Authors: PAPADOPOULOS P. , ROWELL D. L.
Published: July 2006

The reaction of cadmium with calcite was studied with 10−6–10−2M Cd2+ using 4g CaCO3 and 50 ml solution. The calcite‐water suspension was equilibrated for 2 d before adding Cd(NO3)2. The CaCO3 surface has a high affinity for Cd and at < 1 μmol g−1 a linear adsorption isotherm (C‐type) describes the reaction, whereas precipitation of CdCO3 on calcite predominates at higher Cd additions. In the latter case pH decreased and solutions were undersaturated with respect to CaCO3 indicating that CdCO3 prevented the CaCO3 surface from reacting with the acidity generated from CdCO3 precipitation. The data for low Cd additions suggests that an ideal surface solid solution is formed between CdCO3 and CaCO3 and the Thorstenson and Plummer equation expressing the pIAP values of surface solid solutions is valid. Equilibrium was attained for low Cd additions in several minutes, whereas precipitation was a slow process; at the changeover point distinction between the two processes is difficult. The reacting surface area calculated from the maximum adsorption of Cd is 0.5‐1.0 times that measured by the BET method.

The Cd‐reacting surface areas of four natural calcareous minerals were much less than those found by the BET method which includes the surfaces of other minerals present. The Thorstenson and Plummer equation may be a useful way to relate solution composition and carbonate‐adsorbed Cd in contaminated soils.
Reaction kinetics of the adsorption and desorption of nickel, zinc and cadmium by goethite. I. Adsorption and diffusion of metals
Authors: BRUEMMER G. W. , GERTH J. , TILLER K. G.
Published: July 2006

The reactions of Ni, Zn and Cd with goethite were studied over a range of initial metal concentrations (10−6 to 10−4M), pH values (4 to 8), reaction times (2h to 42d) and temperatures (5 to 35°C). The adsorption of metals increased with pH, reaction time and temperature. Adsorption of Ni increased relative to Zn and Cd with increasing time and temperature. The initially rapid adsorption of metals within a few hours was followed by a much slower reaction linearly related to time1/2, interpreted as diffusion–controlled penetration of goethite. The pH–dependent relative diffusion rates (Ni > Zn > Cd) were influenced by both affinity for goethite surfaces and by ionic radius. Diffusion coefficients of the three metals ranged from about 10−19to 10−20cm2s−1. The corresponding activation energies of diffusion were also calculated (Ni 35, Cd 55, Zn 90 kJ mol−1). Our view about the reactions of heavy metals with goethite involves (i) adsorption of metals on external surfaces, (ii) solid–state diffusion of metals from external to internal binding sites, and (iii) metal binding and fixation at positions inside the goethite particles. The general parameters of these processes are related to the hydrolytic properties (pK values) and the ionic radii of the metals. The results show that goethite may be an efficient sink for trace metals.
The determination of the macroporosity of impregnated blocks of a clay soil and its relation to volumetric water content
Authors: MACKIE‐DAWSON L. A. , MULLINS C. E. , KIRKLAND J. A. , FITZPATRICK E. A.
Published: July 2006

The bulk density of slices cut from resin impregnated soil blocks was obtained by immersion in paraffin. Total porosity was then calculated using measured density of soil solids and the density of the resin. Macroporosity (> 350 μm) was obtained by image analysis and microporosity was derived as the difference between total porosity and macroporosity. On four separate sampling occasions throughout the year, there was a good agreement between values of microporosity obtained in this way and volumetric water contents measured at the time of sampling.
Transformation of poorly‐crystalline oxides during boiling with NaOH to concentrate iron oxides from soils
Authors: GOODMAN B. A. , BERROW M.L. , RUSSELL J. D.
Published: July 2006

The effect of boiling 5 M NaOH on the nature of poorly crystalline iron oxides in some iron pans from Scottish soils has been investigated by IR and Mössbauer spectroscopy in conjunction with XRD. In samples that contained goethite and other crystalline oxides there was substantial production of goethite from the less well‐defined phases as a result of the alkali treatment. Neither kaolinite nor humic acid, when added to the samples, was effective in preventing this transformation, although some inhibition was observed. There was, however, no goethite production with a pan that had no crystalline iron oxides, although this could be stimulated by the addition of small amounts of either goethite or haematite. The practice of using the boiling alkali method routinely for the concentration of crystalline iron oxides in soils should, therefore, be considered carefully, since any co‐existing crystalline and non‐crystalline phases are likely to lead to the transformation of the latter to goethite.
The genesis and classification of soils on wet terraces and moraines in New Zealand
Authors: MEW G. , LEE R.
Published: July 2006

Six soils on glacial outwash terraces and one on moraine are discussed; four are formed partly in loess of unknown age. Evidence of podzolization is apparent in all profiles, but the vertical drainage under very high rainfall is insufficient to remove surplus water. Gley processes appear to dominate, in a perched‐water environment.

Podzolic B horizons were identified in the same five profiles following both the Canadian system and that used by the Soil Survey of England and Wales. However, only three of these profiles could be allocated to existing podzolic subgroups in the latter system. Spodic horizons were identified in a different group of five profiles. Differences in classification are discussed with reference to the criteria used and in relation to proposals for revision of the New Zealand Soil Classification.