bluuebunny/crossref_metadata_2025 huggingface dataset:
OPTIMAL INTERPOLATION AND ISARITHMIC MAPPING OF SOIL PROPERTIES
Authors: BURGESS T. M. , WEBSTER R.
Published: July 2006

Kriging is a means of spatial prediction that can be used for soil properties. It is a form of weighted local averaging. It is optimal in the sense that it provides estimates of values at unrecorded places without bias and with minimum and known variance. Isarithmic maps made by kriging are alternatives to conventional soil maps where properties can be measured at close spacings.

Kriging depends on first computing an accurate semi‐variogram, which measures the nature of spatial dependence for the property. Estimates of semi‐variance are then used to determine the weights applied to the data when computing the averages, and are presented in the kriging equations.

The method is applied to three sets of data from detailed soil surveys in Central Wales and Norfolk. Sodium content at Plas Gogerddan was shown to vary isotropically with a linear semi‐variogram. Simple punctual kriging produced a map with intricate isarithms and fairly large estimation variance, attributed to a large nugget effect. Sloniness on the same land varied anisotropically with a linear semi‐variogram. and again the estimation error of punctual kriging was fairly large. At Hole Farm. Norfolk, the thickness of cover loam varied isotropically, but with a spherical semi‐variogram. Its parameters were estimated and used to krige point values and produce a map showing substantial short‐range variation.
HILL LAND STUDIES IN THE GRAMPIAN REGION OF SCOTLAND
Authors: JONES R. J. A. , TINSLEY J.
Published: July 2006

Factors affecting the growth of mixed grass swards in the Upper Don Basin were studied in two phases: in 1967–68 within the altitude range 260–440 m and in 1969–70 in the range 330–550 m O.D. In the first phase the interaction effects of altitude, aspect and soil parent material on herbage yields and mineral element contents were studied using 24 sites in a 3 × 2 × 2 factorial design, without fertilizer in 1967 and with nil, N. P and NP treatments in 1968. Total yields from 3 cuts at 2 monthly intervals averaged 4.84 tonnes D.M. ha−1 in 1968 with no overall significant altitudinal differences. Application of 75 kg N ha−1 as Nitrochalk raised the yield by over 40 per cent, slightly more in the presence of P on soils derived from mineralogically acidic parent materials. Overall, yields from soils on ‘basic’ materials were at least 25 per cent greater than from the ‘acidic’ ones. Sites with southern aspects mostly oulyielded the northern ones but not significantly so. In the second.phase 3 pairs of ‘acidic’ sites only were used, with an NPK treatment added to the 1968 treatments, and lime for the most acid soils at 550 m O.D. On these highest sites the yields were much reduced by the adverse climatic conditions.

Samples of the dry matter from each treatment, replicate and cut at each site were analysed and the offtakes of N, P, K, Ca and Mg determined as well as the apparent recoveries of N, P, K and Ca from the fertilizers. The constraints of altitude on yield and composition were strongly correlated with the prevailing air and soil temperatures. The practical implications of the findings for upland livestock production are discussed but the detailed correlation and factor analyses of the data are presented in another paper.
RELATIONSHIPS BETWEEN NET REDISTRIBUTION OF Al AND Fe AND EXTRACTABLE LEVELS IN PODZOLIC SOILS DERIVED FROM LOWER PALAEOZOIC SEDIMENTARY ROCKS
Authors: ADAMS W. A. , RAZA M. A. , EVANS L. J.
Published: July 2006

Examination of the translocation and net redistribution of Al and Fe in podzolic soils on Lower Palaeozoic sedimentary rocks has shown marked differences in behaviour between the two elements. Iron exhibits the classical pattern of eluviation and illuviation, the consequences of which are closely correlated with amounts of ‘active’ Fe extracted with pyrophosphate. On the other hand Al rarely accumulates in B horizons enriched in Fe. In addition pyrophosphate‐extractable Al is unrelated to its net redistribution pattern. Stagnopodzols on Lower Palaeozoic sediments are strongly acidic throughout and show a characteristic trend in oxidation/reduction conditions with depth. It is the differential response of Al and Fe to the combination of these properties, particularly in relation to their effect on illuviation, which accounts for the observations.
A REAPPRAISAL OF SOIL MAPPING IN AN AREA OF SOUTHERN SCOTLAND. PART I THE RELIABILITY OF FOUR SOIL MAPPING UNITS AND THE MORPHOLOCICAL VARIABILITY OF THEIR DOMINANT TAXA
Authors: RAGG J. M. , HENDERSON R.
Published: July 2006

A two stage random sample survey was made to study the composition of four common soil mapping units already mapped in the Central Lowlands of Scotland. The four mapping units were sampled at densities proportional to their mapped area. In terms of their A horizon textures, the mapping units had percentage reliabilities of 84, 96, 93 and 97 and drainage class reliability scores of 70, 80, 72 and 70. On the basis of taxonomic units within the mapping units, percentage reliabilities ranged from 43–66 but no minor constituent soil exceeded 16 per cent in any of the units studied. Although complex according to currently accepted guidelines, such mapping units should be named according to the dominant taxonomic unit. Errors of identification due to inadequate definitions of taxonomic units have contributed to some of the low levels of reliability of taxonomic units within mapping units and soil taxa should be defined more precisely in Scotland.

Means and variances of the taxonomic units, upon which the above named mapping units are based, indicate that the four taxonomic units (and hence also mapping units) under study are not equally variable in the area of investigation.
A REAPPRAISAL OF SOIL MAPPING IN AN AREA OF SOUTHERN SCOTLAND. PART II THE USEFULNESS OF SOME MORPHOLOGICAL PROPERTIES AND OF A DISCRIMINANT ANALYSIS IN DISTINGUISHING BETWEEN THE DOMINANT TAXA OF FOUR MAPPING UNITS
Authors: HENDERSON R. , RAGG J. M.
Published: July 2006

Results of a two‐stage random sample survey were used to give information about the usefulness of some soil morphological properties for distinguishing between the four taxonomic units, all gley or gleyed soils.

A multivariate logistic method of discriminant analysis was used. The classifications by soil surveyors and by the statistical analysis were mainly in good agreement, but many generally accepted B horizon criteria used for assessing hydromorphism were of little value in discriminating between the soils under study. Depth to gleying and secondary lithology, were valuable distinguishing properties while the matrix colour value, texture and structure of the B horizons were useful in some instances.

Serious consideration of the role of statistical techniques, such as discriminant analysis, is advocated both as a guide to those who design soil taxonomies and as an aid to field identification.
THEORY OF TIME RESPONSE OF TENSIOMETERS
Authors: TOWNER G. D.
Published: July 2006

The time taken for a tensiometer to reach equilibrium with the soil‐water pressure is a function not only of the tensiometer characteristics but also of the soil‐water transport properties. When. in an appropriate system of units. the numerical value of the conductance of the tensiometer cup is small compared with that of the hydraulic conductivity of the soil, and the sensitivity of the pressure ‘gauge’ is large compared with the differential water capacity of the soil. then the precision of the measurements is such that the observed response may be indistinguishable from that of a tensiometer in bulk water. referred to as ‘tensiometer limited’.

The theory developed in this paper for a hemispherical tensiometer cup shows that tensiometer‐limited conditions can be achieved in practice. Moreover. such conditions would often correspond to a rapid response system. It is suggested that it might be advantageous in the design of a field recording system to choose a tensiometer‐limited system even if it is not the fastest realisable one in order that its response is completely predictable from the known tensiometer characteristics. independent of the unknown soil properties. which may be changing.
PHYTOTOXINS IN PERIODICALLY WATERLOGGED FOREST SOILS
Authors: SANDERSON P. L. , ARMSTRONG W.
Published: July 2006

The concentration of iron(II), manganese(II), ethylene, volatile fatty acids (VFAs) and hydrogen sulphid have been determined in peaty forest soils subject to waterlogging. Although VFAs would merit further investigation, iron(II) seems to be the only toxin likely to accumulate in sufficiently large quantities to cause root damage.

The use of the ion selective electrode for sulphide measurements is criticized.
A METHOD FOR STUDYING MICROBIAL ACTIVITY IN INTACT SOIL CORES
Authors: OSBORNE G. J. , POOLE N. J. , DREW ELIZABETH A.
Published: July 2006

Carbon dioxide evolution from soil is generally considered to be an indication of actively metabolising biomass. This paper describes a method for studying carbon dioxide evolution from intact soil cores. It also introduces the possibility of using the method in studies of biomass using fumigation techniques.
WATER FLOW IN SOIL MACROPORES III. A STATISTICAL APPROACH
Authors: GERMANN P. , BEVEN K.
Published: July 2006

Two regression equations describing water movement in saturated macropores in the field are compared with a theoretical expresion of the form Qmaα e2ma where Qma is the saturated volume flux density through a macropore system of porosity ema. The theoretical exponent of 2 agrees fairly well with the analyses of two very different sets of field experiments by Burger (1922–1940) and Ehlers (1975). It is suggested that the relationship Qma= Q*e2ma may be a useful first approximation to predict macropore flow, where Q* is an empirical coefficient that is expected to depend on the hydraulic connectivity, geometrical structure, tortuosity, roughness and other properties of the macropore system.
A METHOD OF PREDICTING BULK DENSITY CHANGES IN FIELD SOILS RESULTING FROM COMPACTION BY AGRICULTURAL TRAFFIC
Authors: BLACKWELL P. S. , SOANE B. D.
Published: July 2006

A simplified soil mechanical model was constructed to predict compaction beneath agricultural wheels when running on soils of certain characteristics. Soil strength functions were developed from in situ measurements of field soils and some laboratory measurements. Soil strain was measured by surface sinkage and changes of dry bulk density by gamma‐ray transmission methods. Soil stresses were measured by deformable spherical transducers and compared to predicted stresses using equations developed by Söhne. A method of analysis was devised to identify a form of the virgin compression line from field data. Changes of the slope and intercept of this line were monitored over a range of moisture contents for two soils and used in the prediction model.

The prediction model was tested against compaction measured during independent experiments at different sites. Good prediction was found for soils of initial dry bulk density greater than 1.1 g cm−3 and cone resistance greater than 500 kPa, using a 30°, 12.9mm diameter cone. On looser and weaker soils the predicted compaction was often less than measured values.

Using the model for simulation of compaction beneath a range of wheels revealed that contact pressure alone can be a misleading guide to compaction. Increases of bulk density below 10cm are considerably influenced by wheel load. The most effective way of reducing compaction requires the use of both a minimum load and a maximum contact area.
SOME NEW EQUATIONS TO DESCRIBE PHOSPHATE SORPTION BY SOILS
Authors: SIBBESEN E.
Published: July 2006

Phosphate sorption was studied on surface and subsurface soils sampled from the old field experiments at Askov, Denmark. Two empirical three‐parameter equations, an extended Freundlich and an extended Langmuir equation are proposed and compared with the Langmuir, the Freundlich, the ‘double’ Langmuir, the Gunary, and the Fitter‐Sutton equations.

In the proposed equations the affinity parameter of the Langmuir equation and the exponent of the Freundlich equation are replaced by the term Bc −D the value of which decreases with increasing phosphate concentration, c. On average the Freundlich equation thus modified yielded the closest fit to the sorption data. This was followed by the Fitter‐Sutton, the modified Langmuir, the ‘double’ Langmuir, the Gunary, the Freundlich, and finally the Langmuir equation. Out of the three equations that yielded the closest fit to the sorption data the correlation between the parameters within the equations, furthermore, was least for the proposed extended Freundlich equation. Therefore, this equation may be generally suitable for describing phosphate sorption by soils.
TITRATIONS OF FULVIC ACID FRACTIONS I: INTERACTIONS INFLUENCING THE DISSOCIATION/REPROTONATION EQUILIBRIA
Authors: DAVIS H. , MOTT C. J. B.
Published: July 2006

Potentiometric titrations were performed on solutions of a polysaccharide fraction and a polycarboxylic acid fraction of fulvic acid. Accurate titration end points were determined by the application of Gran's equivalence point techniques.

Reverse titrations did not follow identical paths to the forward ones because hydroxyl ions were consumed after the end points of the titrations against alkali had been reached. Analyses of the dissociation and reprotonation data demonstrate that electrostatic interactions alone cannot account for the calculated equilibria. The anomalous dissociation/reprotonation equilibria can be explained by the existence of inter‐ and intramolecular hydrogen bonds among functional groups on the fractions.
TITRATIONS OF FULVIC ACID FRACTIONS II: CHEMICAL CHANGES AT HIGH PH
Authors: DAVIS H. , MOTT C. J. B.
Published: July 2006

The stability in solution of a polycarboxylic acid fraction and a polysaccharide fraction of fulvic acid was investigated by pH stat titrations. At pH 8.0 alkali‐consuming reactions occurred on the polycarboxylic acid fraction. At pH 10.0, these alkali consuming reactions were continuing steadily after 22 days. It is suggested that hydroxylation of bound Al may contribute significantly to the consumption of alkali by the fraction. The data indicated that alkali consuming reactions occurred on the polysaccharide fraction at pH 10.0, but not at pH 9.0 and below. Evidence is discussed which indicates that a ‘peeling process’, by which end reducing sugars are stripped off polysaccharide chains and transformed to saccharinic acids, could account for the alkali consumption on this fraction.
TRANSFORMATION OF 15N‐LABELLED AMMONIUM IN TWO SOILS DIFFERING IN NH+4‐FIXING CAPACITY
Authors: FISCHER W. R. , PFANNEBERG T. , NIEDERBUDDE E.‐A. , MEDINA R.
Published: July 2006

Two soils differing in ammonium fixation capacity were incubated for 127 days with 15N‐ammonium sulphate. In a gley soil with high NH+4‐fixing capacity caused by smectites with a charge up to 0.8 per formula unit, the major part of the added ammonium was first fixed by minerals and then released slowly during incubation. The proportion of labelled N in the nitrate fraction increased during the first weeks and then decreased permanently. In contrast, in a histosol with low NH+4‐fixing capacity, the exchangeable fraction contained most of the labelled NH+4, this being highly available to microorganisms and therefore subject to nitrification. About 50% of the added 15NH4 was lost from the histosol in 127 days, but only about 20 per cent was lost from the gley soil.
NITRATE LOSSES IN SOIL DRAINAGE WATERS IN RELATION TO WATER FLOW RATE ON A DECIDUOUS WOODLAND SITE
Authors: TRUDGILL S. T. , PICKLES A. M. , BURT T. P. , CRABTREE R. W.
Published: July 2006

The nitrate load in drainage water from a freely‐draining calcareous soil under deciduous woodland increased consistently as the rate of water flow increased, suggesting that nitrate was rapidly available and not readily exhausted.
CHANGES IN THE PHYSICAL AND CHEMICAL PROPERTIES OF A MINERAL TOPSOIL UNDER THE INFLUENCE OF PEAT DEBRIS
Authors: COYLE E. , COLLINS J. F.
Published: July 2006

Changes are reported of particle size distribution, organic carbon and nitrogen values, cation exchange capacity and exchangeable cation populations, and in iron and aluminium patterns as a result of adding varying rates of acid peat debris to a mineral topsoil. Up to 3 cm of peat had beneficial effects on soil chemical and physical properties but 5 to 8 cm was sufficient to cause considerable acidification, release of Fe and other ions from primary minerals and the development of an iron seam (or pan) which contains up to 7 per cent free iron. Greater thickness of peat (up to 30 cm) caused soil reaction to drop to pH 4 or less and produced so much humic acids as to inhibit iron precipitation and to facilitate its removal from the profiles. The effects of soil moisture on the pattern of peat humification in the deeper additions (20–30 cm) are also outlined.
ANALYSIS OF THE POTENTIOMETRIC TITRATION OF NATURAL AND SYNTHETIC POLYCARBOXYLATES
Authors: YOUNG S. D. , BACHE B. W. , WELCH D. , ANDERSON H. A.
Published: July 2006

Potentiomctric titrations of a variety of natural and synthetic poly‐COOH's varying in molecular weight and COOH density gave pKm values varying from 3.5 to 5.2. The pattern of carboxylic acid group dissociation is discussed in terms of purely electrostatic assumptions and of COOH group clustering. Synthetic polymaleic acid showed many of the characteristics of both fulvic and humic acids, and therefore seems to be a reasonable representation of an average, hypothetical soil organic matter polycarboxylic acid.
FORMATION OF MICROBIAL BIOMASS DURING THE DECOMPOSITION OF 14C LABELLED RYEGRASS IN SOIL
Authors: CERRI C. C. , JENKINSON D. S.
Published: July 2006

Ryegrass uniformly labelled with I4C was incubated aerobically at 25°C for 62 days in two contrasting soils, a near‐neutral (pH 6.8) palcudalf from England and a strongly acid (pH 3.6) haplorthox from Brazil. Decomposition of the labelled plant material was faster in the near‐neutral soil throughout the whole of the incubation period. In neither soil did the addition of fresh plant material significantly accelerate the evolution of CO2 from organic matter already in the soil, i.e. there was no priming action.

In the near‐neutral soil there was a rapid build up of labelled microbial biomass in the first 6 days, followed by a much slower increase that continued throughout the whole incubation period. After 62 days 22.5% of the labelled C remaining in the near‐neutral soil was in the biomass. The yield coefficient (the fraction of the incoming plant C converted to microbial C) of this stabilized or ‘resting’ biomass was 0.15.

Much less labelled microbial biomass was formed in the acid soil than in the near‐neutral soil. By the end of 62 days only 6.2% of the labelled carbon remaining in the acid soil was in the biomass. Biomass C measurements in strongly acid soils must however be treated with caution as the technique used has not yet been adequately validated for such soils.
OPTIMAL INTERPOLATION AND ISARITHMIC MAPPING OF SOIL PROPERTIES. IV SAMPLING STRATEGY
Authors: BURGESS T. M. , WEBSTER R. , McBRATNEY A. B.
Published: July 2006

A sampling strategy is presented for soil survey in which an individual soil property is of interest and can be measured. It depends on first determining accurately the semi‐variogram for the property, and this must be done in a prior reconnaissance stage of a survey. Then from the semi‐variogram estimation variances can be found for any combination of block size and sampling density by the methods of kriging. Alternatively for a given block size the sampling density needed to achieve a predetermined precision (maximum estimation variance) can be determined. The strategy is optimal in the sense that the sampling effort is the least possible to achieve the precision desired. An equilateral triangular configuration of sampling points is best where variation is isotropic, but a square grid at the same density is very nearly as good, and will usually be preferred for convenience. Where there is simple anisotropic variation optimal sampling is achieved by choosing a rectangular grid with sides in the same proportion to one another as the slopes of the semi‐variogram in the directions of maximum and minimum variation.
Variation in soil temperature with microrelief and soil depth in a newly planted forest
Authors: BOCOCK K. L. , BAILEY A. D. , HORNUNG M.
Published: July 2006

Spatial variability in exponential mean soil temperature for a full year in a newly planted forest in northern England was examined using the sucrose inversion method of temperature measurement. The exponential mean temperature decreased significantly with soil depth (P < 0.001). The rate of this decrease varied significantly between different areas of the forest with slightly different soil profiles (0.001 < P < 0.01). Exponential means for 30–50cm depth in the forest and comparable arithmetic means for the nearest meteorological stations were similar. Exponential mean temperatures at 5 cm soil depth were, on average, 1.5° higher in the ridges than in the adjacent flat areas (P < 0.001). The exponential mean for the flat areas was, on average, 0.3° higher to the south‐west of the ridge than to the north‐east (0.001 < P < 0.01). It was also 0.9°C lower than the mean at 5 cm depth in the neighbouring rides (0.001 < P < 0.01).
Distribution of carbon, nitrogen, phosphorus, sulphur, and acidity in two molecular weight fractions of organic matter in soil chronosequences
Authors: GOH K. M. , WILLIAMS MARY R.
Published: July 2006

Ten different topsoils from three soil chronosequences were pretreated with 0.1 m HCl and 0.1 m HCl: 0.3 m HF, then extracted with neutral 0.1 m Na4P207, followed by 0.5 m NaOH. Pretreatments and extracts were purified and fractionated into two nominal molecular weight (MW) fractions (> 50000 and < 50000) using gel filtration. The distribution between the two MW fractions of total carbon (C), nitrogen (N), phosphorus (P), sulphur (S), total acidity, and carboxyl (COOH) acidity and their ratios relative to C were determined. Organic matter in the > 50000 MW fraction contained lower N, P, S and acidity ratios relative to C than those of the < 50000 MW fraction. The chemical nature ofthe > 50000 MW fraction remained unaffected by soil development or vegetation, whereas that of the < 50000 MW fraction changed with soil age and appeared to be influenced by vegetation. The results strongly suggest that two chemically different extractable fractions of organic matter can be isolated from most soils, represented by the active fraction (< 50000 MW) and the relatively large (> 50000 MW) and less active (passive) fraction. A three‐phase system of organic matter is proposed comprising the two extractable fractions and the non‐extractable component.
Organic matter and water‐stable aggregates in soils
Authors: TISDALL J. M. , OADES J. M.
Published: July 2006

The water‐stability of aggregates in many soils is shown to depend on organic materials. The organic binding agents have been classified into (a) transient, mainly polysaccharides, (b), temporary, roots and fungal hyphae, and (c) persistent, resistant aromatic components associated with polyvalent metal cations, and strongly sorbed polymers. The effectiveness of various binding agents at different stages in the structural organization of aggregates is described and forms the basis of a model which illustrates the architecture of an aggregate. Roots and hyphae stabilize macro‐aggregates, defined as > 250 μm diameter; consequently, macroaggregation is controlled by soil management (i.e. crop rotations), as management influences the growth of plant roots, and the oxidation of organic carbon. The water‐stability of micro‐aggregates depends on the persistent organic binding agents and appears to be a characteristic of the soil, independent of management.
Simplification of a model for ion adsorption on oxide surfaces
Authors: POSNER A. M. , BARROW N. J.
Published: July 2006

The adsorption equation of Bowden et al. (I 977) was modified so that adsorption at a constant pH could be described by three parameters. One of these parameters represents the maximum adsorption. The second is the product of three characteristics. These are the binding constant for the adsorbing ion; the proportion of the adsorbate present as that ion; and the electrostatic potential in the plane of adsorption before adsorption had started. The third parameter indicates the rate at which the electrostatic potential in the plane of adsorption changes as adsorption increases. With these modifications, the adsorption equation may be linearized and graphs used to estimate the parameters. This simplification may be of value either when there is no data for the charge characteristics of the surface, or when there is insufficient computer expertise to fit more complex models.
A qualitative field test for locating zones of anoxic soil
Authors: BATEY T. , CHILDS C. W.
Published: July 2006

A field test for ferrous ions, based on the formation of a red complex between Fe2+ and α, α′‐dipyridyl, is shown to be useful in identifying anoxic zones in a cultivated soil. The test can be used in two ways—either a pinch of soil is added to a vial containing reagent or the reagent can be sprayed directly on to a freshly exposed soil surface. The latter way allows the location, size, and pattern of anoxic zones to be observed in situ. Soil in which Fe2+ ions were detected had higher ammoniacal‐N and lower nitrate‐N concentrations than soil which gave a negative reaction to the Fe2+test.
Comparative rates of leaching of chloride, nitrate and tritiated water under field conditions
Authors: CAMERON K. C. , WILD A.
Published: July 2006

The rate of leaching of 36Cl‐, 15NO‐3 and HTO were measured in two experiments under field conditions following the application of irrigation water (40mm and 80 mm) and under winter rainfall (71 mm and 156 mm excess over evaporation). Nitrate and chloride leached at about the same rate, which was on average 23 per cent faster than that of HTO, but with a smaller difference under winter rainfall. It is concluded that although HTO is not an accurate marker for nitrate leaching, ‘bomb’ tritium gives a rough guide to the dating of nitrate pulses in porous rock.
Some observations on the desorption and distribution behaviour of copper with soil components
Authors: McLAREN R. G. , WILLIAMS J. G. , SWIFT R. S.
Published: July 2006

The ability of copper adsorbed by soil components to desorb back into solution was studied by means of experiments using radioactive 64Cu. It was demonstrated that the amounts of copper which can be readily desorbed from soil components are very small.

A dialysis equilibration technique was used to examine the distribution of adsorbed copper between individual materials in a multi‐component system. Where only adsorption of copper was involved, the distribution of copper between soil materials was found to agree with predictions based on adsorption studies with individual materials. However, where desorption was involved, as in the experiments on the redistribution of copper between components after an initial adsorption, the results were strongly governed by the poor reversibility of copper adsorption.

It is clear that desorption or lack of desorption is very important in affecting plant availability of indigenous or added soil copper and in controlling the distribution of copper added to soils.
The influence of iron oxides on phosphate adsorption by soil
Authors: BORGGAARD O. K.
Published: July 2006

Soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite‐EDTA (DE) to dissolve crystalline iron oxides. The phosphate adsorption capacities of the extracted soils were taken as the maximum quantity of phosphate adsorbed computed from the Langmuir equation. The decreases in the phosphate adsorption capacity following EDTA extraction and DE extraction were attributed to the removal of iron oxides. Close correlations (P<0.001) were found (i) between EDTA‐extractable iron (amorphous iron oxides) and the decrease in phosphate adsorption capacity following EDTA extraction, and (ii) between the difference between DE‐extractable iron and EDTA‐extractable iron (crystalline iron oxides) and the further decrease in phosphate adsorption capacity following DE extraction.

The phosphate adsorption capacity, estimated to be approximately 2.5 μmol P m−2, was in good agreement with the capacity of various synthetic iron oxides. The calculated phosphate adsorption capacity of soil iron oxides, obtained from the contents and specific surfaces of amorphous and crystalline iron oxides together with the phosphate adsorption capacity per m2 for synthetic iron oxides, compared favourably with the measured phosphate adsorption capacity.
Denitrification loss from a grassland soil in the field receiving different rates of nitrogen as ammonium nitrate
Authors: RYDEN J.C.
Published: July 2006

Denitrification loss from a loam under a cut ryegrass sward receiving 0, 250 and 500 kg N ha−1 a−1 in four equal amounts was measured during 14 months using the acetylene‐inhibition technique. The rate of denitrification responded rapidly to changes in soil water content as affected by rain. Mean rates of denitrification exceeded 0.2 kg N ha−1 day−1 only when the soil water content was >20% (w/w) and nitrate was >5μ N g−1 in the upper 20 cm of the profile and when soil temperature at 2 cm was >5–8°C. When the soil dried to a water content <20%, denitrification decreased to <0.05 kg N ha−1 day−1. Highest rates (up to 2.0 kg N ha−1 day−1) were observed following application of fertilizer to soil at a water content of about 30% (w/w) in early spring. Denitrification in the control plot during this period was generally about a hundredth of that in plots treated with ammonium nitrate. High rates of N2O loss (up to 0.30 kg N ha−1 day‐1) were invariably associated with high rates of denitrification (> 0.2 kg N ha−1 day−1). However, within 2–3 weeks following application of fertilizer to the plot receiving 250 kg N ha−1 a−1 the soil acted as a sink for atmospheric N2O when its water content was >20% and its temperature >5–8°C. Annual N losses arising from denitrification were 1.6, 11.1 and 29.1 kg N ha−1 for the plots receiving 0, 250 and 500 kg N ha−1 a−1, respectively. More than 60% of the annual loss occurred during a period of 8 weeks when fertilizer was applied to soil with a water content >20%.
Mercury intrusion porosimetry of some New Zealand soils in relation to clay mineralogy and texture
Authors: CHURCHMAN G. J. , PAYNE D.
Published: July 2006

Pore size distributions in the 10/104 nm e.c.d. range in aggregates from three New Zealand soils with largely monomineralic clay fractions, were determined by mercury porosimetry after oven drying and also after critical point drying following methanol and then CO2 exchange from a range of water contents.

A soil containing halloysite showed considerable porosity in the fine pores (10–30 nm) regardless of the method of drying. A smectitic soil showed virtually no porosity in the 102–104 nm range when oven dry. A soil containing allophane was dominated by large pores (> 103 nm). The change from a fine (clayey) to a coarser (clay loam) texture within the profile of one soil was reflected in an increase in large pores.
Multiscale sources of spatial variation in soil. II. A non‐Brownian fractal model and its application in soil survey
Authors: BURROUGH P. A.
Published: July 2006

Stochastic fractals (for example, the fractional Brownian noises) model the often observed power law relation between the variance of a soil property and the length of transect sampled, but fail to account for abrupt changes of the mean (i.e. soil boundaries), for second‐order stationarity and for the non self‐similarity of variations at different scales that are observed in real data. This paper proposes a non‐Brownian, nested model to account for situations where differences of soil have been caused by superimposed, independently acting soil‐forming processes having different weights and acting at separate, discrete scales. The model is explained and theoretical examples of the semivariograms and confidence limits that arise from it are given. The model is applied to three sets of experimental data and is found to give a remarkably good fit where lateral mixing of soil has been negligible and soil boundaries are sharp. The implications for efficient mapping in situations where the soil results from a number of superimposed, independent causes are discussed.
Variation in yield between two similar sandy loam soils. I. Description of soils and measurement of yield differences
Authors: COSTIGAN P. A. , GREENWOOD D. J. , McBURNEY T.
Published: July 2006

Yields of seven different vegetable crops on one site were always much less than those on another nearby site despite the soils on both sites being of the same soil series and the incorporation of large quantities of fertilizer immediately before drilling.

Severe restriction of growth on the poorer site always occurred when the plants were small. Experimental evidence showed that this restriction could not be attributed to a worse aerial environment or a poorer supply of soil nitrogen. Although there were differences in soil physical conditions these seemed unlikely to be sufficient to reduce the growth of young plants.

Plants on the poorer site had much lower potassium and slightly lower phosphorus and water contents than plants on the other site.

It is argued that restricted growth results from the inability of the poorer site to supply sufficient potassium and possibly phosphorus to the crop in the early stages of growth. It was also shown that these nutrient stresses could not be significantly relieved by incorporating fertilizer in any quantity, in the usual way, before drilling.
The variability in soil particle size test results by various subsampling techniques
Authors: SMITH R. B. , PRATT D. N.
Published: July 2006

Analysis of the results of 104 personnel who determined the particle size distribution of 16 different soil‐size materials indicated that there was an effect of subsample preparation. Subsamples prepared using a chute splitter tended to be coarser than those prepared by coning and channelling. This effect was observed for material retained on 425 μm and 75 μm sieves from a variety of soil types. The results confirm those obtained on artificially prepared mixes. The conclusion is that the chute splitter is a more reliable method for obtaining the test portion than coning and channelling.
Influence of iron oxides on the non‐specific anion (chloride) adsorption by soil
Authors: BORGGAARD O. K.
Published: July 2006

Soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite‐EDTA (DE) to dissolve crystalline iron oxides. The amounts of chloride adsorbed by the extracted soils from 1 m NaCl at pH 5 and pH 7 were determined.

The differences (ΔCl) between chloride adsorption at pH 5 and pH 7, attributed to variably charged groups, decreased when iron oxides were removed by EDTA and DE extraction. Close correlations (P>0.001), with negligible intercepts, were found (i)between EDTA‐extractable iron (amorphous iron oxides) and the decrease in ΔCl following EDTA extraction, and (ii) between the difference between DE‐extracted iron and EDTA‐extractable iron (crystalline iron oxides) and the further decrease in ΔCL following DE extraction.

The difference between ΔCl for acetate‐extracted and DE‐extracted samples was calculated from the contents and specific surfaces of amorphous and crystalline iron oxides, together with ΔCl per m2 for synthetic iron oxides. Calculated and measured values were in very good agreement, indicating that soil iron oxides, in relation to chloride adsorption, may be treated as if they consist of only two fractions.
Iron oxyhydroxides in soils developed from Lower Palaeozoic sedimentary rocks in mid‐Wales and implications for some pedogenetic processes
Authors: ADAMS W. A. , KASSIM J. K.
Published: July 2006

Lepidocrocite and goethite are pedogenetic crystalline Fe oxyhydroxides in the soils of mid‐Wales. Lepidocrocite is more abundant and widespread, occurring in brown earths (Denbigh series) as well as morphological gleys. It is commonly dominant in horizons intermediate in depth. Goethite occurs in subsoils and was found to be dominant in the subsoil of surface water gleys (Cegin series). Apart from the Cegin series, a large proportion of the total free Fe occurs in non‐crystalline forms. This amounted to 50–80% of the free Fe in organic and eluvial horizons of podzols. Despite lower proportions of non‐crystalline Fe in Bs horizons, amounts were similar to those in eluvial horizons. Data on the distribution of crystalline and non‐crystalline free Fe together with correlations observed between Fe and C extracted by pyrophosphate suggest that transformation and translocation of Fe in the podzols examined are governed by its association with organic fractions.
The extraction of Fe and Al by 0.1 M pyrophosphate solutions: a comparison of some techniques
Authors: LOVELAND P. J. , DIGBY P.
Published: July 2006

Fe and Al were extracted by 0.1 M pyrophosphate solutions from six replicate samples of seven soils by different, widely‐used techniques, viz. those of the Soil Survey of England and Wales, the Canadian Soil Survey and the United States Soil Conservation Service. The effects of K‐ versus Na‐pyrophosphate solution, and of a difference in the pH of the latter were also investigated. All the techniques gave both different, and a wide spread of, values for Fe and Al in all soils. No one technique was consistently the least variable for both elements. Replicate determinations using each technique were so variable that comparison of results obtained by the different techniques cannot be made with confidence.
Soil water regimes of soils developed on Keuper Marl
Authors: McGOWAN M.
Published: July 2006

The deeper horizons of soils developed on Keuper Marl (Worcester Series) often remain unsaturated during the winter, with corresponding high tensions, even when the surface layers are waterlogged. Re‐wetting of the deeper layers is restricted because of the inherent low volume of coarse pores in the Bt horizon and because the small volume of desiccation cracks formed during the summer soon disappear on re‐swelling. It is suggested that this unexpected water regime may not be uncommon in soils developed on clay‐shale sediments and that the soil drainage (wetness) classes recognized in England and Wales may need to be modified.
The over‐estimation of clay and the under‐estimation of pores in soil thin sections
Authors: MURPHY C. P. , KEMP R. A.
Published: July 2006

The amounts of clay visible in four thin sections from paleosol horizons (clay contents 9–32%) were measured by point counting. These sections were used as references for visual estimates, without point counting, of the amounts of clay in 14 further sections. The measurements and estimates were recorded on pore‐free and gravel‐free bases so they could be related to gravimetric analyses. Amounts of clay measured and estimated by area in these thin sections were between 1.6 and 3.1 times those determined gravimetrically.

The reasons for these differences are discussed. Firstly, clay in soil thin sections contains much pore space beyond the resolution of the optical microscope and has an apparent density dependent on the amount of submicroscopic pore space. An edge effect also causes over‐estimation of clay in soil thin sections and under‐estimation of visible pore space. Components (clay, mineral grains, pores) are usually sloped at their borders with each other within the standard 25–30 μm (three‐dimensional) thin sections. Clay, for instance, may overcap a pore at its border, hiding some pore space. The need for true two‐dimensional images of soil pore patterns in image analysis is indicated.

A nomogram has been constructed, using apparent density, to allow estimation of clay in thin sections of soils with any clay content. Coarse/fine ratios can be determined more accurately and estimates of clay can also be recalculated to provide illuvial to total clay ratios that are more meaningful. It is recommended that the micromorphological identification criterion for the argillic horizon be reassessed and that 4% illuvial to total clay in a soil thin section be adopted as the diagnostic cut‐off.
The wetting and drying of a grazed and ungrazed clay soil
Authors: REID I. , PARKINSON R. J.
Published: July 2006

A 4 year field experiment clearly demonstrates the role played by desiccation cracks in the redistribution of rainfall during the autumn re‐wetting of a Windsor Series clay soil. Where topsoil structure is damaged by the trampling of grazing animals, cracks are well developed and a portion of rain water is diverted down them, by‐passing the topsoil. Redistribution takes place from two centres, the bottom of the cracks and the surface. But where structure is unaffected by trampling, the soil accommodates seasonal shrinkage without cracking and redistribution is by diffusion from the surface only. Summer evaporation is shown to be linearly related to Penman's potential evapotranspiration over a wide range of soil moisture deficits, and simple constants are provided to correct ET to obtain EA. The M.A.F.F. method of estimating evapotranspiration is shown to be too conservative and fails to identify the October maximum soil moisture deficit common in this soil.
Determination of the nitrogen composition of colliery spoil
Authors: PALMER J. P. , MORGAN A. L. , WILLIAMS P. J.
Published: July 2006

Freshly exposed unameliorated spoil and vegetated spoil were analysed for their nitrogen constituents using methods devised for soils. The main components found were non‐exchangeable ammonium (25%), hydrolysable nitrogen (33%) and unidentified non‐hydrolysable nitrogen (62%). Summation of these exceeded 100% because hydrolysis with 6 M HCI extracted much of the non‐exchangeable ammonium. Ammonium in the hydrolysate accounted for over 90% of hydrolysable nitrogen in freshly exposed unameliorated spoil and 70% of hydrolysable nitrogen in vegetated spoil. Correction for this ammonium in the hydrolysate allowed estimates of ‘recent organic’ nitrogen accumulation to be made. These estimates were significantly correlated with spoil mineralizable nitrogen levels. The nature of the nitrogen constituents of colliery spoil and the use of ‘recent organic’ nitrogen estimates in assessing site fertility are discussed.
Thermoluminescence dating of soils developed in Late Devensian loess at Pegwell Bay, Kent
Authors: WINTLE A. G. , CATT J. A.
Published: July 2006

Thermoluminescence (TL) measurements on the present organic surface soil and two buried soils in loess and colluvium derived from loess at Pegwell Bay, Kent, suggest that the signal is almost completely zeroed during soil development, mainly by optical bleaching. The technique may therefore be used to date buried soils developed in loess and possibly other terrestrial sediments. Decalcification, gleying and other soil‐forming processes may also affect the TL signal of the soil parent material, and seem to be the main reasons why the Btg horizons of the Early Holocene buried soil at Pegwell Bay give more recent TL dates than the parent calcareous loess.
Experimental simulation of the results of clay translocation in the B horizons of soils; the formation of intrapedal cutans
Authors: AKAMIGBO F.O.R. , DALRYMPLE J. B.
Published: July 2006

A series of laboratory experiments designed to simulate the formation of intrapedal cutans was carried out through repetitive leachings of undisturbed blocks of soils (6 × 3 × 4 cm3) by suspensions (0.3% concentration) of clay‐sized particles from two commonly occurring Bt horizons in southern England. After leaching, thin sections were cut and point‐counted, thus enabling the visual recognition, replication and potential quantification of newly formed intrapedal pore and grain cutans. They all exhibit morphological, physical and optical properties diagnostic of illuviation cutans, and can be differentiated from inherited cutans on these and on spatial grounds. A general relationship between numbers of newly formed cutans and increasing leaching cycles was observed, and experimental support obtained from these soils for the significance of the complex, three‐dimensional spatial pattern of tubular pores in the translocation of clay‐sized materials and the formation of these argillic, Bt horizons. This study highlights both the value and difficulties of designing laboratory‐based, soil/water/gravity studies in pedology.
Transport and deposition of dilute colloidal suspensions in soils
Authors: VINTEN A. J. A. , NYE P. H.
Published: July 2006

Transport and deposition of suspended particles occur during many soil processes. The mechanisms of removal of particles from suspension during saturated flow are described, and a simple equation of depth filtration is used to test experimental data. A method for labelling dilute clay suspensions with 14C‐paraquat is developed. Particles are removed from flowing suspension even when they are dispersed. The depth filtration equation holds only under these conditions, though the mechanisms of removal of particles from suspension by the soil are unclear. A surprisingly large reduction in flow rate accompanies passage of dilute clay suspensions through soil columns.
Losses of nitrogen by denitrification from a grassland soil fertilized with cattle slurry and calcium nitrate
Authors: EGGINTON GWEN M. , SMITH K. A.
Published: July 2006

Losses of N by denitrification from an imperfectly drained grassland soil were measured by the acetylene‐inhibition technique over a 1‐yr period, during which applications of up to 200 kg ha −1 of N as cattle slurry or calcium nitrate were made. The quantities of N lost from nitrate‐treated soil were much greater than from slurry‐treated areas, and ranged up to 21% of the N applied. The losses occurred predominantly over brief periods following fertilizer application in the spring. Ratios of N released as N2 to that released as N2O increased as denitrification rates increased. The highest ratio recorded, 24, may have been a conservative estimate because inhibition of N2O reduction may not have been complete on all occasions. Increased respiration was observed in the soil profile as a result of adding C2H2. This effect should be taken into account in interpreting experiments using the C2H2‐inhibition technique.
Structure of a silty soil in relation to management
Authors: DOUGLAS J. T. , JARVIS M. G. , HOWSE K. R. , GOSS M. J.
Published: July 2006

In the United Kingdom silty soils have been classified as unsuitable for direct drilling since these soils may produce seed‐beds that are inadequate for satisfactory crop emergence. This judgement was based on problems encountered in the first 2–3 yr of direct drilling as well as on an appreciation of soil physical properties. Longer‐term experimentation (10 yr) has indicated that, subsequent to that initial period, soil conditions after zero‐tillage are not a major limitation to growth of autumn‐sown cereals. This eventual parity between simplified and conventional tillage can be attributed largely to improvement in the surface of direct‐drilled land. In the tenth experimental year this layer comprised more strongly developed aggregates, of greater stability, than those from the annually ploughed soil. Porosity and soil strength measurements did not indicate that root growth would be severely restricted below this depth. When this soil was wet in winter it was weak and relatively unstable and so it would most likely be unsuitable for sequential direct drilling of spring‐sown crops.

At the same site soil that had been continuously under grass throughout the same 10 yr period developed better structure than that in the arable area, in part because of a greater earthworm population and an increased organic matter accumulation. In any subsequent change to arable usage this improved structure would best be conserved by avoiding soil inversion and using direct drilling or some other simplified method of cultivation.