bluuebunny/crossref_metadata_2025 huggingface dataset:
Drop‐cone penetration in situ and on minimally disturbed soil cores
Authors: CAMPBELL D. J. , HUNTER R.
Published: July 2006

Drop‐cone penetration was measured both in situ and on minimally disturbed cores at a selection of soil matric potentials for four soils. The drop‐cone penetration/water content relation was linear in situ and, if results for very low water contents were excluded, for the cores. The slope of the line for the field data was much greater than for the core data and this raises doubts about the value of other than in situ measurements of soil strength for predicting field behaviour. Vane shear strength is negatively correlated with in situ drop‐cone penetration. The drop‐cone test is a useful strength test for small volumes of soil, but care must be taken in selecting the mass of the cone as this affects the volume of soil which will influence the test results.
A statistical study of seven curves for describing the sorption of phosphate by soil
Authors: RATKOWSKY D. A.
Published: July 2006

summary

Seven mathematical models, which have been advanced for describing phosphate sorption by soils, are studied here with respect to their statistical behaviour in estimation. These seven non‐linear regression models include the Langmuir equation and two extensions of it, the Freundlich equation and two extensions of it, and Gunary's equation. Measures of non‐linear behaviour, such as the Bates & Watts (1980) curvature measure of intrinsic non‐linearity and the Lowry & Morton (1983) asymmetry measure of non‐linearity, were calculated for each model in combination with each of six data sets. It was found that the Freundlich equation and the extension of it proposed by Sibbesen behaved best, with Gunary's equation also having acceptable statistical properties, whereas the Langmuir equation and its extensions behaved worse, exhibiting properties which indicate that the estimators of their parameters would be severely biased and non‐normal in distribution. It is believed that similar conclusions may apply to other processes involving surface adsorption.
Nitrogen in particle size fractions of soils incubated for five years with 15N‐ammonium and 14C‐hemicellulose
Authors: CHRISTENSEN B. T. , SØRENSEN L. H.
Published: July 2006

Four soils with a range of clay and silt contents were incubated for 5 a with 15N‐labelled (NH4)SO4 and 14C‐labelled hemicellulose and then fractionated according to particle size by ultrasonic dispersion and sedimentation. The distribution of labelled and native N between clay, silt and sand fractions was determined and elated to previous results on the C distributions.

Between 29% and 48% of the added N was found in organic form. The 15N atom percentage excess decreased in the order: clay > whole soil > silt > sand. For both clay and silt, the enrichment factor for labelled and native N decreased with increasing fraction weight. Clay enrichment was higher for labelled than for native N, the converse being true for silt. The distribution of whole soil labelled organic N was: clay 77–91%, silt 4–11%, and sand <0.5%. Corresponding values for native N were 69–74%, 16–22%, and 1–2%, respectively.

All soils had higher proportions of labelled than of native N in the clay, the converse was true for the silt. The C/N ratio of the native silt organic matter was higher and that of clay organic matter lower than whole soil C/N ratios. Differences between the C/N ratio distributions of native and labelled organic matter were small.

The relative distribution of labelled N and C was very similar confirming that the turnover of C and N in soil organic matter is closely interrelated.
Reclamation of colliery spoil: the effect of amendments and grass species on grass yield and soil development
Authors: RIMMER D. L. , GILDON A.
Published: July 2006

Results are presented of a field trial in which various methods for the reclamation of coarse colliery waste were tested. The site was divided into three blocks and each block received a different level of deep cultivation; however, these treatments appeared to have no long‐term significant effect on grass yield. Within each cultivation block a number of treatments were superimposed. These included: amendments of soil and organic materials, deep placement of P fertilizer, and the use of different grass seed mixtures. Grass yield was measured annually for 6 years. At the end of that period soil samples were taken for analysis and tests were conducted in the field to measure the effects of treatments on the developing soil conditions. There was a general decline in grass yields during the course of the experiment. However, the rate of decline varied with the different treatments, being lower on amended spoil (i.e. treated with soil or organic materials) and on treatments sown with a seeds mixture containing S143 cocksfoot (Dactylis glomerata). Differences in the soil conditions resulting from the use of amendments were detected; in particular, the soil‐amended plots had higher pH and exchangeable Ca and greater penetrability.
Mobile iron, aluminium and carbon in sandy coastal podzols of Fraser Island, Australia: a quantitative analysis
Authors: LITTLE I. P.
Published: July 2006

In this paper podzols of free‐draining sands in south‐eastern Queensland are examined. The 14 profiles represent a chronosequence from young incipient podzols, to ancient ‘giant podzols’ of Pleistocene age, with a spodic horizon at a depth of 8–10 m.

Carbon, Fe and Al were determined in pyrophosphate, and Fe, Al and Si in oxalate extracts. The resulting profile distributions were modelled by three expressions, fitted for each attribute, which accounted for surface accumulation, B horizon development and a phase (B/C horizon) of constant composition with depth.

The parameters may be used to characterize soil profiles. They show that there is a tendency for the accumulation of carbon in the B horizon to be reflected by Fe and particularly A1 accumulation, which supports the proposition that carbon is directly associated with the transport of A1 and Fe.

A feature of many of these soils is a deeply weathered surface with little tendency for commensurate development of an illuvial horizon. Rates of removal of Fe and Al from the A horizon were obtained by comparison of the depths of leaching with age estimates based on geomorphology, and they indicate a non‐linear rate of increase in the thickness of the A horizon.
On the fractal dimensions of some transient soil properties
Authors: ARMSTRONG A. C.
Published: July 2006

Spatial variation of soil properties can be studied by use of the concept of fractals, and the overall roughness of a surface characterized by its fractal dimension. Soil surface strength was recorded by both cone penetrometer and field shear vane, along a series of transects, at 10 cm spacings. In the natural state, such data gave fractal dimensions very close to 2, implying an almost totally random data set, and only the deliberate action of cultivations introduced an order of persistence. Microtopography, measured by a profile meter at 1 cm intervals, had fractal dimensions of 1.7 on two separate sites. Problems are identified specifically in the choice of a suitable model for fitting the semi‐variogram, and in the collection of an efficient data set.
Contributions by fungi and bacteria to aggregate stability of cultivated soils
Authors: MOLOPE M. B. , GRIEVE I. C. , PAGE E. R.
Published: July 2006

Stability changes during ageing (sterile) or incubation (non‐sterile) of both natural field aggregates and remoulded aggregates from five soils were studied for periods up to 30 days. Growth of fungal hyphae, estimated by ergosterol measurement, corresponded to temporary stability increases in both types of aggregates during the first 15 days. Thereafter, fungal hyphae disappeared and were replaced by actinomycetes and bacteria. Increased stability due to entanglement by hyphae was comparable to that due to thixotropy in remoulded aggregates. Bacterial growth accompanied the fall in stability associated with fungal decline, but had little direct effect in stabilizing soil aggregates. Destruction of polysaccharides by periodate oxidation greatly diminished aggregate stability. The role of bacterial polysaccharides in soil aggregate stability is discussed.
Torus‐shaped pedological features associated with soil microorganisms
Authors: SULLIVAN L. A. , KOPPI A. J.
Published: July 2006

Torus‐shaped features 1–7 urn in diameter were found on the smooth surfaces of the structural units of a Red Podzolic Soil (Udic Haplustalf) B horizon and on the smooth surfaces within the columnar structures of a Solodized Solonetz (Typic Natrustalf)‐SEM & EDS were used to characterize these features, and to determine their probable pedogenesis. The size range was bimodal in the Red Podzolic B horizon, being either ∼5 μm or ∼2.0 um. In the Solodized Solonetz all tori were ∼ 1.5 μm in diameter. The larger tori consisted of fine‐clay coated collapsed fungal spores, whilst the smaller tori were fine‐clay coated collapsed bacteria‐sized cells.
Composition and properties of poorly ordered minerals in Welsh soils. I. Composition
Authors: ADAMS W. A. , KARIM M. I. , GAFOOR S. N.
Published: July 2006

Eleven horizons of acidic soils in mid‐Wales developed from Lower Palaeozoic sedimentary rocks were examined. Selective extraction of Al and Si provided evidence against the occurrence of significant quantities of poorly ordered Al‐silicates. Fe0 was weakly correlated with Al0, but very closely correlated with Al0 minus Al extracted by cold 5% Na2CO3, implying that poorly ordered Al occurs in part as a substituent in Fe oxide and in part in a form unassociated with Fe oxide. Support for this was obtained by analysis of oxide fractions concentrated from aqueous suspensions by sequential ultracentrifugation and through the examination of synthetic Al‐substituted Fe oxides. Fe oxide containing Al substituted at an almost constant level was the dominant constituent of the poorly ordered fraction in four of the five Bs horizons examined. The occurrence of Al in this form is an important mechanism by which Al is retained in aerobic but highly acidic Bs horizons.
Interpretation and presentation of cone resistance data in tillage and traffic studies
Authors: O'SULLIVAN M. F. , DICKSON J. W. , CAMPBELL D. J.
Published: July 2006

Recommendations are made regarding the analysis and presentation of cone resistance data. Methods for eliminating extreme readings due to stones are compared and the effects of stones on variability and treatment comparisons are discussed. Results showed very high variability between positions, even at 100 mm separation. Measurements separated by more than 1 m were independent of each other except where trends in other soil properties influenced cone resistance. The assessment of compaction under wheels is described for cone resistance measurements made under the rut centre‐line. Parameters are derived from measurements made on two‐dimensional, vertical grids to quantify the depth, extent and intensity of compaction and loosening. The usefulness of penetrometers in tillage and traffic studies is discussed.
Gaseous diffusion through peat
Authors: KING J. A. , SMITH K. A.
Published: July 2006

Relative gas diffusivity (D/D0) was measured in peat cores equilibrated to set moisture tensions between zero and ‐ l0 kPa, using the radioactive gas 85Kr. A relationship between relative diffusivity and the air filled porosity was obtained, which showed lower values of D/D0 at air‐filled porosities above about 0.13m3m−3, and higher values at porosities below about 0.10m3m−3 than some of those found in the literature for mineral soils. The likely effects of shrinkage behaviour on drying in the field, on the relationship between D/D0 and air‐filled porosity, are discussed.
Estimating hydraulic conductivity values from ring infiltrometer measurements
Authors: YOUNGS E.G.
Published: July 2006

Infiltration from ring infiltrometers of different radii was measured into four soil materials contained in laboratory tanks. The infiltration per unit area was larger the smaller the ring size, coming to a steady state at an earlier time. Scaling based on similar media theory was applied to the results using a microscopic characteristic length defined in terms of the hydraulic conductivity of the saturated soil and a macroscopic characteristic length taken as the radius of the ring. The relationships between scaled cumulative infiltration and scaled time merged into a single relationship at small scaled times for all soil materials and for all sizes of ring, but were different for the different soils and for the various ring radii at large scaled times. The relationship at small times was used as a type curve to interpret in situ measurements with ring infiltrometers on three field soils in terms of the hydraulic conductivity of the saturated soil. These estimates of hydraulic conductivity pertained to the small volume of soil near the surface which was wetted during the measurement. Large variations in hydraulic conductivity values were found from experiments with small sized rings, but little variation was found for large sized rings. The technique provides a simple method of investigating soil structural changes near the surface.
Fate of nitrogen in cattle slurry following surface application or injection to grassland
Authors: THOMPSON R. B. , RYDEN J. C. , LOCKYER D. R.
Published: July 2006

Two field experiments commencing in winter (December) and spring (April) were conducted to determine the fate of nitrogen (N) in cattle slurry following application to grassland. In each experiment three methods of application were used: surface application, and injection ± the nitrification inhibitor, nitrapyrin. Slurry was applied at 80t ha−1, (≡248 kg total N ha−1in the winter experiment, and 262 kg N ha−1in the spring experiment). From slurry applied to the surface, total losses of N through NH3volatilization, measured using a system of wind tunnels, were 77 and 53 kg N ha−1respectively for the winter and spring experiments. Injection reduced the total NH3volatilization loss to ∼2 kg N ha−1. Following surface application, loss by denitrification, measured using an adaptation of the acetylene‐inhibition technique, was 30 and 5 kg N ha−1for the two experiments. Larger denitrification losses were observed for the injected treatments; in the winter experiment the loss from the injected slurry without nitrapyrin was 53 kgN ha−1, and with nitrapyrin 23 kgN ha−1. Total denitrification losses for the corresponding injected treatments in the spring experiment were 18 and 14 kg N ha−1. Apparent recoveries of N in grass herbage in both experiments broadly reflected the differences between treatments in total gaseous loss.
Factors affecting formation of methyl nitrite in soils
Authors: MAGALHÃES A. M. T. , CHALK P. M.
Published: July 2006

The formation of CH3ONO in 11 soils treated with HNO2or NaNO2in a closed system, was studied by measuring the concentration in the gas space above the soil and by absorbing CH3ONO in HI. The gaseous concentration of CH3ONO increased and then decreased following additions of HNO2or NaNO2, and the production of CH3ONO increased with increasing concentrations of HNO2or NaNO2added to soils.

The amounts of CH3ONO trapped in HI were 13.5 to 20.4 times higher than those determined by integrating under the net production curves. The evolved CH3ONO amounted to 0.4 to 3.5% of added NO2−, and 4.2 to 50% of the gaseous forms of N absorbed by acidic KMnO4solution. The CH3ONO evolved from soils was positively correlated with the methoxy content of the soils, and inversely related to soil pH, with negligible amounts being evolved from alkaline soils. The results show that CH3ONO is a product of NO2−decomposition in soils, and indicate that small concentrations of the gas may be produced in N–fertilized soils in which NO2−accumulates.
Modelling water movement in drained clay soil. II. Application of the model in Evesham series clay soil
Authors: JARVIS N. J. , LEEDS‐HARRISON P. B.
Published: July 2006

A two‐domain model of water movement, storage and drainage in a cracked clay soil has been applied and tested in the field by irrigating an instrumented lysimeter constructed around a 2.0 m length of mole drain. Measurements of drain outflow rates and of increases in soil water content were compared with model predictions. The model predicted satisfactorily the peak drain outflow rate and subsequent drain recession although there was a tendency for the model to underestimate the time to the start of drainage. Good agreement with the measured recharge profile was generally found.
The estimation of mineralization, immobilization and nitrification in nitrogen‐15 field experiments using computer simulation
Authors: BARRACLOUGH D. , SMITH M. J.
Published: July 2006

A combination of mathematical analysis and computer simulation, using parameters readily measured in a nitrogen‐15 field experiment, is employed to determine rates of mineralization, immobilization and nitrification under a growing crop. The procedure also yields the proportion of crop nitrogen uptake occurring as ammonium and nitrate.

When applied to ‐results from grass lysimeters receiving 250 or 900 kg N ha–1 a–1 as ammonium nitrate, the analysis suggested that at 250 kgN ha–1 a–1 64–66% of crop nitrogen uptake was as ammonium; at 900 kg N ha–1 a–1 the figure was 43–49%. Nitrification at 250kgNha–1 was only 13–19kgN ha–1 over 160d while at 900 kg N ha–1 between 191 and 232 kg N ha–1 were nitrified.

The results suggested that the apparent inhibition of nitrification in grassland soils may simply reflect poor substrate competition by nitrifying bacteria. Finally, there was a suggestion that mineralization/immobilization was lower at the high fertilizer rate.
Distribution coefficients of Cd, Co, Ni, and Zn in soils
Authors: ANDERSON P. R. , CHRISTENSEN T. H.
Published: July 2006

Batch adsorption experiments were conducted with a mixture of solutes at low equilibrium concentrations of Cd (0.7‐12.6 μg1−1), Co (18‐118μg1−1, Ni (22‐330 μg 1−1), and Zn (40‐1480 μg1−1) in 38 different soils. Statistical correlations indicated that metal sorption onto the soils was influenced by the presence of clays and hydrous oxides of Fe and Mn. Based on calculated distribution coefficients for these metals, Co will generally exhibit the highest mobility in soils, but the mobility of Zn will increase faster with decreasing pH. Two types of empirical relationships are developed from these data to estimate values for the distribution coefficients.
Two mechanisms for age‐hardening of soil
Authors: DEXTER A. R. , HORN R. , KEMPER W. D.
Published: July 2006

Soil samples from Germany, Israel and USA were moulded at water contents around the lower plastic limit and compacted with uniaxial pressures c. 20‐200 kPa. The samples were stored at constant water content. At intervals after moulding, the strengths of sub‐samples were measured with a small penetrometer.

The soils showed increases in strength with time. Two types of behaviour were observed and explained by a simplified theory for soil strength. With the German and Israel soils, penetrometer strength increased by the same absolute amount irrespective of compaction pressure. This indicates that new particle‐particle bonds were being formed at a rate which was not affected by compaction. With the USA soils, the ratio of penetrometer strength/initial strength increased with time and was independent of compaction pressure. This indicates that existing particle‐particle bonds were being reinforced by a cementation mechanism. Evidence is presented which suggests that age‐hardening by this second mechanism may be inhibited by soil organic matter.
The effect of soil texture on the dissolution of North Carolina phosphate rock
Authors: KANABO I. A. K. , GILKES R. J.
Published: July 2006

Laboratory investigations of the dissolution of North Carolina phosphate rock (PR) in soil, as affected by soil texture, were conducted using soils created by mixing various proportions of the <45 μm and >45 μm fractions of a lateritic soil. The dissolution of PR in soil, and the resulting changes in plant available P, were estimated by measuring increases in exchangeable Ca (ΔCa) and NaHCO3‐extractable P (ΔPb), respectively. The total fertilizer phosphate dissolved (ΔP) was calculated from δCa values based on the assumption that dissolution of PR released amounts of Ca and P in a constant ratio determined by the stoichiometry of the PR. δP increased with increasing content of <45 μm particles. APb also increased with the percentage of <45μ fraction, with about 20% of AP being recovered as APb. A smaller proportion of dissolved P was soluble in NaHCO3 for the soil comprising only the <45μ particles. The increase in δP with increased percentage of <45 μn soil was probably due inter alia to the greater P‐sorption, Ca‐sorption and the pH buffering capacity of the fine grained soil constituents.
Quantity/intensity and quantity/potential studies in Na–Ca exchange system in some salt‐affected soils
Authors: KOTUR S. C. , RAO T. SESHAGIRI
Published: July 2006

The Q/Icurves for Na in the Na–Ca system in some salt‐affected soils of Malaprabha and Ghataprabha river valleys lacked the curvature commonly seen in the Q/I curve for potassium. The Malaprabha soils showed lower AR0Na, NaL and BC0Na values and higher energies of replacement of calcium by sodium than the Ghataprabha soils; the latter showed a higher affinity for Na than Ca. Two distinct linear parts of the quantity/ potential curves, with different slopes, indicated that Na is held in these soils in two characteristic types of exchange sites having different affinities for sodium. The intersection of the two linear parts corresponded to ESP values in the range of 13 to 64%. The change in the affinity at such a high degree of Na saturation was attributed to the presence of chloritized smectitic clays and sodium‐selective zeolite, such as analcite, reported in these soils.
Correlations between extractable Na, K, Mg, Ca, P & N from fresh and dried samples of two Aquults
Authors: GILLIAM F. S. , RICHTER D. D.
Published: July 2006

Significant increases in extractable ions resulted from air‐drying and grinding samples of two infertile Aquults. Effects of the sample preparation differed markedly between ions and between the two soils. Regression equations were calculated to predict extractable ions in dried, ground samples from extractable ions in fresh, unground samples and the relationships were compared between the two soil series. Regressions were significantly different between soils for extractable PO34, Mg++, and K+, but not for Ca++ and Na+. Extractable NH +4 and NO‐3 in fresh, unground samples were not correlated with those in air‐dry, ground samples of either soil. Differences in response to preparation between soil types appeared to be related to the oxidative status of these soils in the field, wherein constituents of more poorly‐drained soils may be less stable to the oxidizing conditions of air‐drying and grinding. Such complexities suggest that effects of sample preparation should be considered when interpreting soil nutrient data for studies of forest nutrient cycling and forest soil fertility.
Gas diffusion, fluid flow and derived pore continuity indices in relation to vehicle traffic and tillage
Authors: BALL B. C. , O'SULLIVAN M. F. , HUNTER R.
Published: July 2006

Relative gas diffusivity, air permeability and hydraulic conductivity were measured in undisturbed soil cores from tillage and traffic experiments. Continuity indices were taken as the quotient of relative diffusivity and air‐filled porosity, and of air permeability and air‐filled porosity (and the square of air‐filled porosity). These were applied to individual measurements or to treatment means. More general continuity indices were derived from the changes in flow or diffusion with porosity, where the variations in porosity were due to both field variability and applied changes of water potential. These indices were the exponent in the relationship between relative diffusivity and air‐filled porosity and the slope of log–log plots of air permeability and air‐filled porosity or hydraulic conductivity and degree of saturation. Some physical significance was attached to the exponents by comparison with models of soil porosity. Positive intercepts of the relative diffusivity or air permeability plots on the air‐filled porosity axes were taken as porosities blocked to gas movement.

Continuity indices and flow measurements showed differences between tillage and traffic treatments which did not necessarily reflect differences in bulk density. Intrinsic permeability was better estimated from air permeability than from unsaturated hydraulic conductivity.
A micromorphometric method for estimating change in the volume of soil induced by weathering
Authors: MORAN C. J. , McBRATNEY A. B. , KOPPI A. J.
Published: July 2006

A stereological and spatial‐statistically based method for the volumetric estimation of weathering of an in situ soil profile is described. The technique uses the distances between, and size of, zircon grains in undisturbed, horizontal, thin sections. Results are presented as volume attenuation indices, describing the decrease which occurs when a volume of soil material is developed from a given volume of parent material. The method allows computation of confidence intervals for the index and precursory quantities. A soil profile developed in granodiorite, near Bathurst in New South Wales, Australia, is examined to illustrate the technique. The results appear consistent with field description of the profile, with estimates using X‐ray fluorescence analysis (20–90 um sand fraction), and with sand grain counts of the non‐magnetic heavy mineral portion of the same fraction, although the latter methods are of unknown precision.
The influence of sward species composition on the rate of organic matter decomposition in grassland soil
Authors: HOPKINS D. W. , SHIEL R.S. , O'DONNELL A.G.
Published: July 2006

To examine the influence of different plant materials on the rate of organic matter (OM) decomposition in soil, respiration and N mineralization/immobilization were measured during incubation of a test soil to which the plant materials were added. Amendments consisted of sward material either from grassland plots with different amounts of OM accumulation, or material from plants associated with soils having markedly different OM contents. Evolution of CO2from the test soil plus herbage from an experimental plot showing OM accumulation was greater than that from the same soil amended with herbage from plots without accumulation. Apparently, grass species had no significant effect on OM turnover; differences in accumulation in grassland soils must be related to other environmental factors. Decomposition of youngCalluna vulgariswas, however, slower than that of young grass material and in this case species could affect organic matter accumulation.
Inhibition of nitrate accumulation in tropical grassland soils: effect of nitrogen fertilization and soil disturbance
Authors: SYLVESTER‐BRADLEY R. , MOSQUERA D. , MÉNDEZ J. E.
Published: July 2006

In acid soils in the Eastern Plains of Colombia, forage grasses planted on land prepared before the previous dry season produced 40–50% more dry matter than when land was prepared immediately before planting. Virtually no NO3− accumulated in surface (0–10 cm) soil from three native undisturbed savanna sites. Where land was ploughed before the dry season, NO3− levels increased gradually after a 2–3 month lag, and dropped at the beginning of the rains. In samples incubated for 4 weeks, more NO3− accumulated in the wet than the dry season. A similar 2–3‐month lag occurred when land was ploughed after the dry season. NH4+ levels were higher in ploughed than savanna soils, and rose in all soils at the beginning of the rains. More NO3− and NH4+ accumulated on incubation in pots than in soil cores. Forage grasses inhibited NO3− accumulation in the soil, relative to plant‐free plots, and legumes stimulated it. N fertilization overcame this inhibition except in the case of Brachiaria humidicola.
Analysis of cone resistance data with missing observations below stones
Authors: GLASBEY C. A. , O'SULLIVAN M. F.
Published: July 2006

When stones prevent the measurement of cone resistance, and missing values below the stones are ignored, then averages can be seriously underestimated. Methods are considered for correcting this bias and an algorithm is proposed in which missing observations are replaced by their expected values. A numerical example gives results in close agreement with those obtained using the optimal, but computationally expensive, method of maximum likelihood estimation. It is recommended that data from incomplete penetrations should not be discarded but should be used, preferably with the proposed algorithm, to reduce the bias in estimates of mean values.
The macroporosity of artificial aggregates of varying texture
Authors: SHIEL R. S. , ADEY M. A. , SHANNON J. B.
Published: July 2006

Artificial soil blocks were made by mixing either ballotini or natural sand with a suspension of silt and clay (fines). The soil was allowed to dry, shrinkage was measured, and from thin sections, the type, area and size of voids in the horizontal plane were observed. As the fines content increased, from 0 to 25%, packing voids (spaces caused by a lack of sufficient small particles to fill voids between sand grains) decreased and were partly replaced by fissures (caused by shrinkage of fines leading to isolated cracks within blocks). From 25% to 50% fines, aggregate shrinkage increased rapidly resulting in the development of large inter‐aggregate voids, but packing voids and fissures decreased. There was a transfer of porosity from within the block to the inter‐aggregate spaces as the fines content increased. Blocks containing coarse sand‐size particles had larger packing voids and fissures, a greater area of fissures, but similar shrinkage to blocks containing fine sand‐size particles.
Effects of sorbed orthophosphate on zinc status in three soils of eastern Canada
Authors: XIE R. J. , MACKENZIE A. F.
Published: July 2006

P‐Zn interactions can affect fertilizer use and produce Zn deficiencies with certain crops. Phosphorus‐Zn sorption‐desorption reactions were studied in topsoil and subsoil samples from three Quebec soils. Soils were equilibrated with P solutions, then with Zn solutions, and finally with solutions containing no P or Zn. The first equilibration evaluated P sorption (Ps), the second evaluated Zn sorption (Zns) after P sorption (Ps), and the third evaluated Zn desorption (ZnD) as related to added P. Subsequently, Zn fractions were extracted sequentially with KNO3 (Znkno3), NaOH (ZnNaOH) solutions and concentrated HN03+ H202(ZnHNO,).

One mmole sorbed P resulted in increases of 0.5 to 1.0 meq (mean = 0.72) increases in cation exchange capacity (CEC). Increased Zns with added P was equivalent to 4 to 5% of the increase in CEC induced by Ps in the Uplands (sand) and St. Bernard (loam) soils, and 0.4 to 0.9% in the Dalhousie (clay) soils, while one meq increase in CEC resulted in 1.5‐3.5% decrease in ZnD. There existed positive correlations between Ps and extractable soil Fe materials. Phosphate sorption enhanced associations between Zns, ZnD or Zn fractions and soil organic or crystalline Fe contents, confirming that P addition increased specific sorption of Zn on Fe components. Other mechanisms including precipitation, P‐induced negative charge and ‘bridge’ effects are also discussed.
Nitrogen mineralization in the field at various soil depths
Authors: HADAS A. , FEIGIN A. , FEIGENBAUM S. , PORTNOY R.
Published: July 2006

The accumulation of mineral nitrogen was measured in the field in five soil‐layers between 0 and 120 cm, in two plots of a long‐term experiment contrasting high and low fertilizer inputs. Soil temperature and moisture were also determined. The total quantity of mineral N that accumulated in the 0‐120 cm soil layer during 11 weeks in the summer was 138 and 78 kg ha−1, 25% and 45% of which were found below 60cm, in the high and the low fertility plots, respectively. Nitrogen mineralization in the field was predicted by a model which takes account of changes in temperature and moisture content of the soil. The potentially mineralizable N for this model was found from laboratory incubation experiments. The measured amount of mineralized N was 13 to 26% less than the predicted amount.
Diffusion of methyl bromide in soil
Authors: MIGNARD E. , BENET J. C.
Published: July 2006

Phenomenological modelling is proposed for penetration by diffusion with aqueous dissolution of a gaseous constituent in non‐saturated soil when there is a thermodynamic imbalance between this gas phase constituent and the same constituent in solution. Non‐equilibrium experiments (Mignard & Benet, 1986) led to specifying the equation governing the kinetics of dissolution and measurement of the phenomenological coefficient for methyl bromide.

The results of the model with dissolution imbalance are compared with those of models in the literature which assume immediate dissolution equilibrium in the treatment of soil with methyl bromide applied at the surface. The model developed gives profiles of concentration of substance in the soil in both liquid and gas phases, and makes it possible to judge the extent of the soil zone treated and to forecast what will be the behaviour of the substance.
Seasonal changes in the structure of clay soils in relation to soil management and crop type. I. Effects of crop rotation at Cruden Bay, NE Scotland
Authors: MACKIE‐DAWSON L. A. , MULLINS C. E. , FITZPATRICK E. A. , COURT M. N.
Published: July 2006

Changes in soil structure and macroporosity were investigated using large thin sections and image analysis of photographs taken from fluorescent resin impregnated soil blocks. In this way porosity measurements were combined with visual assessment of the distribution and type of soil pores and aggregates. Three sites were chosen on a clay soil at Cruden Bay, Aberdeenshire, and sampled throughout two growing seasons in order to characterize various stages of a 7‐year rotation.

The seasonal pattern of structural change depended on the crop. During a dry period in April and May 1980, a system of cracks developed on the grass site but not on sites sown to spring barley. The changes in structure on the grass sites could mainly be attributed to changes in water content, and the resulting cycle of shrinking and swelling.

After cultivation, structural changes resulting from settling were evident. Earthworm activity, especially after manure spreading, also had a pronounced effect on structure. Since many of these processes are cyclic in this environment, the resulting structural states showed a pattern of cyclic recurrence.
A multiple ion uptake model
Authors: BOULDIN D. R.
Published: July 2006

A model is developed which describes uptake of Ca, Mg, K, NO3, Cl, and SO4. The electrical neutrality of plant and soil are maintained through exchange of H or OH at the root‐soil interface, constant partial pressure of CO2 and non‐exchangeable H reaction with the soil cation exchange complex.

An important innovation in this model is the inclusion of electrical neutrality as a condition for plant, soil and soil solution. The uptake of cations is a function of both concentration of anions in solution and the suite of exchangeable cations. The model emphasizes an important role for CO2 in soil chemistry and plant nutrition. Presently, the model is most useful for generating research hypotheses. Perhaps the most important hypothesis is that something about as complicated as the present model will be required to model multiple ion uptake and crop yields.
The soil solution chemistry of some Oxfordshire soils: temporal and spatial variability
Authors: CAMPBELL D. J. , KINNIBURGH D. G. , BECKETT P. H. T.
Published: July 2006

The immiscible liquid displacement method was used to displace soil solutions from a variety of Oxfordshire soils. These included grassland, arable, and woodland soils. The results of detailed chemical analyses demonstrated that for most solutes there were significant seasonal differences as well as differences both within and between soil series. The variation over time intervals of a few days or weeks appeared to be relatively small in relation to sampling errors. Median concentrations (in mmol m−3) for soil solutions derived from 21 grassland sites and six arable sites sampled six or seven times throughout 1 year were: pH 7.7, alkalinity 1810, Na 465, K 390, Mg 135, Ca 2120, Sr 1.9, Ba 0.16, Mn 0.52, Fe 3.4, Cu 0.25, TON 860, Cl 1590, S 327, P 64, Si 220, B 5.1, and DOC 4250. For many solutes, the individual soil solution concentrations spanned a range from approximately five‐times less than these median values to approximately five‐times more.
On the Akaike Information Criterion for choosing models for variograms of soil properties
Authors: WEBSTER R. , McBRATNEY A. B.
Published: July 2006

A problem in the application of geostatistics to soil is to find satisfactory models for variograms of soil properties. It is usually solved by fitting plausible models to the sample variogram by weighted least squares approximation. The residual sum of squares can always be diminished, and the fit improved in that sense, by adding parameters to the model. A satisfactory compromise between goodness of fit and parsimony can be achieved by applying the Akaike Information Criterion (AIC). For a given set of data the variable part of the AIC is estimated by
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where n is the number of experimental points on the variogram, R is the residual sum of squares and p is the number of parameters in the model. The model to choose is the one for which Â is least.

The AIC is closely related to Akaike's earlier final prediction error and the Schwarz criterion. It is also equivalent to an F test when adding parameters in nested models.
Cation type and ionic strength effects on the solution composition of an acidic subsoil
Authors: MANSON A. D. , FEY M. V.
Published: July 2006

Sodium, potassium, magnesium and calcium chloride solutions of four concentrations (0.4, 1.0, 4.0, l0.0meq dm−3) and distilled water were equilibrated with the highly weathered, acidic subsoil of a Plinthic Paleudult from Natal at a soil:solution ratio of 2.2:1, then separated by centrifugation with an immiscible liquid and analysed for inorganic solutes. With each salt, increasing ionic strength resulted in lower solution‐pH (the maximum pH was 4.95 in the distilled water equilibration) and higher aluminium concentration and activity. These effects were much less marked for sodium (maximum ΔpH of 0.47) than for the other cations (maximum ΔpH of 0.83) and both the concentration and activity of aluminium were correspondingly lower (by tenfold at the highest chloride concentration) in the sodium solutions.

Irrespective of the nature or concentration of the electrolyte added, pH and the activities of A13+ and silica in solution were consistently interrelated in a way which suggests that equilibrium with the gibbsite and poorly crystalline kaolinite in this soil had been closely approached. The results provide a basis for anticipating the effect of infiltrating solutions of fertilizer salts on subsoil acidity and suggest that a beneficial effect may accrue from the presence of sodium in the cation suite of acid soils.
Phosphorus accumulation in savanna termite mound in Venezuela
Authors: LÓPEZ‐HERNÁNDEZ D. , FARDEAU J. C. , NIÑO M. , NANNIPIERI P. , CHACON P.
Published: July 2006

Nasutitermes ephrataeare often abundant in seasonally flooded and dry Venezuelan savannas, where they play an important role in litter decomposition and nutrient cycling. Measurements were made of phosphorus forms and associated properties in 14 mounds and adjacent soils. Mounds contained on average over twice as much total phosphorus as adjacent soils. The difference was differentially distributed, mainly as inorganic forms. Mounds also display a relatively high organic matter content. ‘Available’ forms of P, especially water‐soluble P, increased several times as a result of termite activity. Concomitantly, P‐sorption was greatly reduced in mounds compared to surrounding soils.

Mounds did not display higher phosphatase activity. The elevated organic carbon content, high level of soluble P, together with very high C/P0ratios found in mounds, probably inhibited phosphatase activity.
Effects of addition of bentonite on the hydrocarbon fraction of a podzol soil (A1 Horizon)
Authors: AMBLÈS A. , MAGNOUX P. , JAMBU P. , JACQUESY R. , FUSTEC E.
Published: July 2006

Lipids generally accumulate in surface horizons of soils deficient in clay minerals. Samples from a podzol (A1 horizon–no clay) were incubated with a supply of hetero‐ or homo‐ionic (Mg)‐bentonite for 4 months at 28 °C. A significant decrease of unbound lipids was observed. A detailed study of the mainly hydrocarbon fraction revealed that several processes were involved. A transfer of lipids, particularly hydrocarbons, occurred from the free to the bound phase. Consequently, reduced toxicity of these lipids towards soil microorganisms can be expected. The addition of clay resulted in a stimulation of oxidation processes, the extent of which varied with the exchangeable cations; heteroionic bentonite led to increased mineralization, whereas Mg‐bentonite promoted mild oxidation reactions. The increased microbial activity also produced short‐chain hydrocarbons; with Mg‐bentonite, unusual C21‐C35 n‐alkanes were detected. All of these microbial hydrocarbons were found in the bound phase.
Effects of pre‐sowing compaction on soil physical properties, soil atmosphere and growth of oats on a clay soil
Authors: McAFEE M. , LINDSTRÖM J. , JOHANSSON W.
Published: July 2006

The effects on a number of soil physical and aeration parameters of compaction during spring pre‐sowing operations were measured on a clay soil (49% clay). A soil‐tyre contact stress of 200 kPa was applied by tractor tyres.

Yield of an oat crop was reduced by 30% as a result of compaction. Total porosity of the soil was reduced by 6% v/v owing to loss of pores > 60 μm, and water retention was increased. The resultant decrease in air‐filled porosity greatly reduced gas diffusion and air permeability coefficients of the soil, and, for a time, O2 content of the soil atmosphere was significantly lowered in the compacted treatment. Penetrometer resistance after sowing was 3.5 MPa in the control and 4.5 MPa in the compacted treatment; in the latter, root growth was inhibited until the soil dried and cracked. By the end of June, canopy temperature measurements indicated water stress in the oat crop on compacted soil but not in that on the control.

The results obtained indicated that air permeability, measured in the field, of 1 mm s−1 provides a satisfactory single value below which crop growth is likely to be reduced.
Aeration changes after irrigation in a clay soil
Authors: McAFEE M. , LINDSTRÖM J. , JOHANSSON W.
Published: July 2006

The effects on soil aeration of varying both the intensity and quantity of water applied per irrigation were investigated in a field experiment on a clay soil. Soil physical and soil aeration parameters were measured before, and for up to 7 days after irrigation. Irrigation increased the volumetric water content of the surface layer by approximately 8% v/v. However, periods of waterlogging were short on this soil. Significant decreases in soil oxygen content in the days after irrigation were caused by increased soil and root respiration. In terms of subsequent crop growth, the practice of applying 30 mm irrigation water at an intensity of 5 mm h−1 was shown to be superior to irrigations providing half this quantity (15 mm) or double this intensity (10 mm h −1). The lower intensity irrigations decreased soil permeability by homogeneous wetting and swelling, and thus more of the water applied was recovered in the soil. Approximately one third of the water applied at the higher intensity was lost through cracks, and wetting of the soil was less uniform.
Scaling the saturated hydraulic conductivity of an alfisol
Authors: BONSU M. , LARYEA K. B.
Published: July 2006

Alfisols exhibit a high degree of spatial variability in their physical properties. As a result, it is difficult to use information on physical parameters measured at one location to model larger‐scale hydrologic processes. In this study, the saturated hydraulic conductivity, KS, of an Alfisol was determined on 109 undisturbed monoliths using the falling‐head permeameter method. The model developed by Arya & Paris (1981) was used to calculate the pore volume from sand and clay fractions. Scaling factors were calculated from the measured Ks, sand pore‐volume, clay pore‐volume, clay content and effective porosity, using the similar media concept. Prediction of Ks of gravelly Alfisol using clay pore‐volume is confounded by high gravel content which, when discounted, improves the prediction remarkably. The scaled mean saturated hydraulic conductivity K* for all horizons of the Alfisol was approximately l.0x 10−5ms−1.
A comparison between acetone and dioxane and explanation of their role in water replacement in undisturbed soil samples
Authors: CHARTRES C. J. , RINGROSE‐VOASE A. J. , RAUPACH M.
Published: July 2006

Undisturbed, moist samples from the A horizon of a swelling grey clay were treated with acetone or dioxane with or without para‐dichlorobenzene to replace soil water. They were then either impregnated with polyester resin whilst still solvent‐wet or after drying. Structural changes in samples treated with dioxane and then impregnated while solvent‐wet indicated little evidence of either disintegration or shrinkage resulting from the treatment. However, samples treated with acetone were prone to disintegration, but this was mitigated somewhat by the addition of para‐dichlorobenzene. Allowing either solvent to evaporate before impregnation caused shrinkage.

X‐ray diffraction and infra‐red studies of treated clay separates indicated that dioxane prevented the marked swelling and potential dispersion found with acetone. It was concluded that dioxane breaks structural bonds within clay interlayers and between soil crumbs, thus limiting both collapse of clay minerals and sample shrinkage on drying. No changes to plasmic fabrics could be seen under a petrological microscope. Because of their appropriate size and shape, dioxane molecules could also enter clay interlayers so preventing marked shrink/swell movements. There is some indication that they may also form epoxide‐like compounds that themselves form structural ‘cements’.
Directional strength in aggregates as affected by aggregate volume and by a wet/dry cycle
Authors: HADAS A.
Published: July 2006

Reduction of aggregate size in the upper, tilled soil layer as a result of one wet/dry cycle was observed for sandy soil and clay soils. Bulk density of aggregates tended to increase as their size diminished for the clay after the wet/dry cycle, whereas similar changes in bulk density for the loam were observed only for aggregates smaller than 5.6 cm. Slaking and water‐drop impact seem to be the major factors in reducing the aggregate size of the sandy loam, while swelling and shrinkage affect clay aggregates of all size groups, but only aggregates smaller than 4.0 mm for the sandy loam.

Tensile strength of the sandy loam aggregates was related to the axis along which the stresses were applied. A definite directional dependence of tensile strength was observed, e.g. the shorter the axis, the larger the tensile strength. The directional strength dependence was apparently not affected by one wet/dry cycle.