bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTRIC CHARGE CHARACTERISTICS OF ANDO A, AND BURIED A, HORIZON SOILS
Authors: WADA KOJI , OKAMURA YUTAKA
Published: July 2006

The electric charge characteristics of four Ando soils (A1 and μA1) and a Chernozemic soil (Ap) were studied by measuring retention of NH4+ and Cl– at different pH values and NH4Cl concentrations. No positive charge appeared in the Ando soils at pH values 5 to 8.5 except for one containing allophane and imogolite. The magnitude of their negative charge (CEC; meq/l00g soil) was dependent on pH and NH4Cl concentration (C; N) as represented by a regression equation: log CEC =a pH +b log C +c, where the values of a and b were 0.113–0.342 and 0.101–0.315, respectively. Unlike the Chernozemic soil, Ando soils containing allophane, imogolite, and/or 2:1–2:1:1 layer silicate intergrades and humus showed a marked reduction of cation retention as pH decreased from 7 to 5. This was attributed to the charge characteristics of the clay minerals and to the carboxyl groups in humus being blocked by Al and Fe.
WET AND DRY PORE SIZE DISTRIBUTION IN A KAOLINITIC SOIL BEFORE AND AFTER REMOVAL OF IRON AND QUARTZ
Authors: HOMSHAW L. G. , CAMBIER P.
Published: July 2006

A kaolinitic soil was treated chemically to remove iron and quartz. Before and after treatment the properties of the soil were, respectively: iron content, 7 and 1%; quartz content, 21 and 0%: water content at saturation (water/kaolin content, g/g), 0.40 for both, of which 0.34 was in pores for which the Kelvin radius rj, was ≤35 nm. Porosity and pore size distribution (PSD) up to this pore size were studied using nitrogen sorption, mercury injection, pressure membrane equilibration and low temperature scanning microcalorimetry (DSC). These analyses justified interpretation in terms of kaolinite content alone. The PSD was unaffected by the removal of iron or quartz or the moisture content of this soil.

New DSC techniques show that the pore spaces within the treated samples (rj≤ 35 nm) are largely unconstricted, and thus, an experimental curve relating temperature depression for melting to pore size is possible using only one sample.
WEATHERING IN TERTIARY GRAVELS IN N.E. SCOTLAND
Authors: KOPPI A. J. , FITZPATRICK E. A.
Published: July 2006

The weathering of highly quartzose flint‐containing gravels, believed to be the remnants of Tertiary beach deposits in N.E. Scotland, has been studied in detail. The deposits also contain infrequent boulders of granite, quartz schists and granulites which are largely kaolinised, but the kaolin varies in crystallinity between the two sites investigated. Quartz, alkali feldspars, muscovite and biotite‐like mica have been variously altered, and the weathering products include fine grained silica and leucoxene.
EFFECT OF VESICULAR‐ARBUSCULAR MYCORRHIZAL FUNGI ON THE RELATIONS OF PLANT GROWTH, INTERNAL PHOSPHORUS CONCENTRATION AND SOIL PHOSPHATE ANALYSES
Authors: STRIBLEY D. P. , TINKER P. B. , SNELLGROVE R. C.
Published: July 2006

The effect of infection by vesicular‐arbuscular mycorrhiza on the predictive value of soil analysis for available P was tested in a glasshouse experiment. Leeks (Allium porrum) were grown on ten Rothamsted soils with a wide range of initial NaHCO3‐soluble P, each of which also received 5 levels of added P. Soils were partially sterilized with 1 Mrad of γ‐radiation, or left untreated; plants on sterilized soil were infected with yellow‐vacuolate endophyte (Glomus mosseae) or left non‐mycorrhizal. The NaHCO3‐soluble P in the soils was measured 5 days after phosphate addition.

Yields from all P levels on all soils were plotted against soil NaHCO3‐soluble P content and separate smooth response curves were obtained for non‐infected and artificially‐infected plants. Infection increased yield only on soils with less than 100 mg P kg−1. In contrast, naturally‐infected plants gave no clearly defined response curve to P, and on three soils the yields were consistently low. These soils gave very low natural infections and had low spore densities probably due to the cropping history of the sites.

Artificially‐infected plants had much higher shoot P concentrations than did uninfected plants of similar dry weight, over a large range of soil phosphate levels; this effect was also noted with the endophyte G. fasciculatus. Naturally‐infected plants showed a poor relationship between shoot P concentration and yield.
SOILS OF THE STATE OF BAHRAIN
Authors: BRIDGES E. M. , BURNHAM C. P.
Published: July 2006

The State of Bahrain lies in the arid zone on the southern side of the Arabian Gulf. The factors influencing soil formation on the Islands are examined and an account given of the soils. These can be placed in four groups: Solonchaks, Regosols, Yermosols and Fluvisols. The Solonchaks of the northern plain contain unprecedented amounts of gypsum which, in the absence of leaching, give rise to a variety of morphological features. The distribution of Regosols, Yermosols and Fluvisols can be related closely to physiographical location throughout the country.
DENITRIFICATION IN A VERY ACID TROPICAL SOIL
Authors: WICKRAMASINGHE K. N. , TALIBUDEEN O.
Published: July 2006

In a very acid upland clay surface soil and with glucose added to give initial C/N weight ratios (added glucose‐C: NO3‐N) in the soil of 0, 2 and 5, the rates of evolution of N2 and N2O were maximum at C/N = 2 but were significantly less at 0 and 5. The total N2 and N2O production was highest at C/N = 0, confirming that increasing amounts of glucose immobilised more nitrate into the biomass.

As with added NO−3‐N, the time lag, preceding a maximum ‘steady state’ rate of N20 evolution, increased regularly with increasing glucose. Within this ‘steady state’ period, the gaseous CO2‐C/(N2+ N2O)‐N weight ratio in the effluent gas are between 1.0 and 1.3, which corresponds well with the stoichiometric ratios of 1.07 and 1.29 for the reduction of NO−3 to N2O and N2 respectively. Before and after this period, this gaseous C/N ratio was much higher.

Denitrification was not observed in subsurface soil even after adding 100 mg kg−1glucose‐C although it contained 4 times as much indigenous nitrate as the surface soil. Inoculating this soil with increasing amounts of the surface soil, up to 15 per cent by weight, induced substantial increases in the rates and amounts of denitrification.

The effects of increasing the soil pH. of introducing increasing oxygen concentrations in the influent gas. and the fate of added NH+4‐N, are briefly reported here. In these experiments. NO−2‐N did not accumulate in the incubated soil nor was there any NH3in the effluent gas. Evolution of N2 only occurred when N2O evolution was in its final stages.
TILTH MELLOWING
Authors: UTOMO W. H. , DEXTER A. R.
Published: July 2006

Effects of weathering action, mainly wetting and drying cycles, on the strength of the clods produced by tillage are studied. Experiments were carried out on sandy loam soils at two sites in South Australia, and on silt loam and clay soils at Wye College, England.

It is found that tillage increases the amplitude of soil water content fluctuations. These bigger soil water content fluctuations resulted in a decrease in the clod strength and this in turn modified the size distribution of the clods produced by tillage in the South Australian soils. The decrease in clod strength, as measured by the drop shatter test, was followed by an increase in the proportion of the smaller aggregate size fraction produced by a second implement pass.

It is suggested that, for soils in which the increase in the soil water content fluctuations after the first tillage implement pass decreases clod strength, a further implement pass should be delayed for several days. By doing this, the soil can be tilled with minimum energy and cost to produce a good seed bed.
THE EFFECT OF SOIL TYPE, SLOPE, RAIN INTENSITY AND THEIR INTERACTIONS ON SPLASH DETACHMENT AND TRANSPORT
Authors: QUANSAH C.
Published: July 2006

From a factorial experiment using a graded sand and three soils (sand, clay loam, and clay), five slopes (0.0, 3.5, 7.0, and 14.0 per cent) and four intensities (50, 80, 110, and 140 mm h−1), splash detachment and splash transport are described in terms of the direct effects and the first and second order interactions of these variables.

The graded sand and three soils tested are significantly different in the mean weight of soil detached and transported. They can be placed in rank order of graded sand, sand, clay, and clay loam with increasing resistance to splash detachment. The amount of material transported is in the order of graded sand > clay > sand > clay loam. For each soil there are significant increases in splash detachment and splash transport with increasing rainfall intensity. Both splash parameters are significantly correlated with slope steepness.

The most important interactions that influence splash detachment and splash transport are soil × intensity and slope × intensity respectively. Significant interactions show that the factors are not independent of each other; the simple effects of a factor differ, and the magnitude of any simple effect varies according to the level of the other factors of the interaction term. These interactions have not been explicitly studied in previous research on splash erosion.

Power equations are established between splash activity and the above variables and reasonable working ranges for the exponents are suggested.
STRUCTURE FORMATION UPON MIXING Na‐MONTMORILLONITE WITH BI‐ AND TRIVALENT ION‐CLAYS1
Authors: FRENKEL H. , SHAINBERG I.
Published: July 2006

The light transmittance of montmorillonite suspensions saturated with Na+, Mg++, Ca++, Al+++, Fe+++ or La+++ and with known mixtures of these ions was investigated. Also, the kinetics of bi‐ and trivalent ion montmorillonite tactoid formation and breakdown was followed by recording changes in light transmission as a function of time when M‐montmorillonite suspensions (M = Mg++, Ca++, Al+++, Pe+++ or La+++) were added to Na‐montmorillonite suspensions of the same concentration in a titrating vessel placed in the light path of a spectrophotometer. Introduction of a small fraction of Na+ onto the exchange complex of M‐clay had no effect on the size of the M‐tactoids. The breakdown of Mg++ and Ca++ tactoids occurred as the equivalent fraction of adsorbed Na+ increased from 0.2 to 0.5, with mixed Na‐M montmorillonite particles having an equivalent fraction of adsorbed Mg++and Ca++ less than 0.3 remaining as single platelets. Conversely, introducing even a small fraction (<10%) of trivalent onto the exchange complex of Na‐montmorillonite caused the formation of tactoids.

Instantaneous formation of an intermediate unstable structure occurred upon mixing Na‐montmorillonite with M‐montmorillonite. It is proposed that edge‐to‐face association stabilizes this intermediate structure, whereas face‐to‐face association stabilizes the eventual tactoids.
A LABORATORY METHOD TO MEASURE GAS DIFFUSION AND FLOW IN SOIL AND OTHER POROUS MATERIALS
Authors: BALL B. C. , HARRIS W. , BURFORD J. R.
Published: July 2006

An apparatus was constructed to measure diffusivity of krypton‐85 and gas permeability in an enclosed core of soil of field structure or in other porous material. Sample enclosure decreased water loss by evaporation, reduced mass flow caused by changes in ambient temperature and pressure during diffusion measurement, and allowed subsequent measurement of gas permeability without further sample disturbance. When a bundle of tubes was used as a test sample to calibrate the apparatus, the resistances to diffusion and viscous flow agreed approximately with those calculated from the tube size and number. Gas movement was measured in dry sieved soil and in undisturbed cores of silty loam soil to illustrate the practical value of the method. In the dry cores, diffusivity relative to free air (DA/Do) was greater in ploughed soil, 0.18, than in direct drilled soil, 0.14, nearly in proportion to the greater air porosity in the ploughed soil, but air permeability in ploughed soil was four times greater than in direct drilled soil and was about 1 000 times greater than in compacted sieved soil.
A PARTIAL MODEL FOR THE RATE OF ADSORPTION AND DESORPTION OF PHOSPHATE BY GOETHITE
Authors: BARROW N. J. , MADRID L. , POSNER A. M.
Published: July 2006

It was assumed that the reaction between phosphate and goethite consisted of a second order forward reaction between phosphate molecules and adsorption sites, opposed by a first order desorption reaction. Because adsorption occurs at a charged surface, it was assumed that the rates were affected by the electrostatic potentials at the surface. A mixed analytic and numeric approach was used in which the rate equation was integrated over small time steps and a computer programme was used to generate the effect of many small steps.

Comparison between the model and results for rate of adsorption suggested that the rate‐determining step preceded the electron transfer steps and did not, of itself, involve electron transfer. With this assumption, rate of adsorption could be modelled with the estimation of only one parameter beyond those needed to model the equilibrium values for adsorption. The model gave a good description of the rate of adsorption at three pH values for times up to one hour. It did not describe the slow adsorption over longer periods and this suggested that a different mechanism was involved. Although the main features were reproduced, description of desorption was less satisfactory. This deficiency of the model may occur because it was restricted to the reaction with phosphate and did not model the rate component for the other changes in charge that accompany adsorption.
SELECTIVE EXTRACTION OF AMORPHOUS IRON OXIDES BY EDTA FROM SOILS FROM DENMARK AND TANZANIA
Authors: BORGGAARD O. K.
Published: July 2006

Soils from Denmark and Tanzania were extracted with EDTA solutions of different concentrations and pH. After extraction for 3 months there was no significant (95% level) further increase in amounts of iron (and aluminium, calcium, and magnesium) during longer extraction periods. X‐ray diffraction showed no change of the crystalline minerals caused by the extraction, which is believed to be specific for amorphous iron oxides. The EDTA method may thus serve as a reference method for the determination of amorphous iron oxides in soils.

Although the difference between EDTA‐extractable iron and that extracted during 2 h by ammonium oxalate at pH 3.0 in the dark may be high, the ammonium oxalate method is considered to give a fast and often fair estimate of amorphous iron oxides.
MODELLING OF SOIL PORES AS TUBES USING GAS PERMEABILITIES, GAS DIFFUSIVITIES AND WATER RELEASE
Authors: BALL B. C.
Published: July 2006

Two models are presented describing the air‐filled continuous pores in soil and how they change with soil water potential. In the first model (A), the pores are represented by tortuous tubes of uniform radius. The radius, length and number are calculated from air permeability, relative diffusivity and air‐filled porosity measured at each soil water potential. In the second model (B), the pores are represented by tortuous tubes of three radii joined at random in series. The radii and total lengths of the tube sections are estimated by comparison of air permeability, diffusion coefficient and air‐filled porosity at each water potential with values calculated for a large number of theoretical systems.

The models were applied to the results from undisturbed cores of a silt loam taken from 30 to 80 mm depth. For both models, the sequences of continuous pores were estimated to be 2 to 7 times as long as the sample but shortened as the sample dried. From the second model the average pore radius in direct drilled soil, 0.3 mm, was half that in ploughed soil and the minimum radius, 0.1 mm, was one‐quarter that in ploughed soil.
MOISTURE RELEASE CHARACTERISTICS AND POROSITY OF TWELVE SCOTTISH SOIL SERIES AND THEIR VARIABILITY
Authors: BACHE B. W. , FROST C. A. , INKSON R. H. E.
Published: July 2006

Moisture release characteristics were measured in triplicate at nine sites for each of twelve soil series. Water content was linearly related to log suction for loamy soils, but a strongly curved relationship was found for dominantly sandy or clayey soils. Some series were highly variable, due mainly to textural variations within series, but texturally uniform series were less variable. The largest significant differences between series were given by the drainable pore space of B horizons, a useful property for drainage design advice; for some series drainable pore space indicated a different permeability than might have been expected from natural profile morphology.
PHOSPHATE ADSORPTION IN ALLOPHANIC SOILS
Authors: IMAI H. , GOULDING K. W. T. , TALIBUDEEN O.
Published: July 2006

The kinetics and heats of phosphate adsorption were measured on the <2 μm Na‐saturated fractions of three allophanc‐rich soils from Japan. Between 50 and 2250 μmol P g−1 as sodium phosphate were added to the soil fractions at pH 5 and pH 7, and at initial concentrations of 5 and 25 × 10−4m to avoid aluminium phosphate precipitation.

An initial ‘instantaneous’ adsorption associated with exposed sites and, simultaneously, two inverse exponential rates of adsorption on internal and freshly forming external sites were observed. These rates are attributed to changes in the microstructure of allophane and to the desorption of organic matter held on allophanic surfaces. This interpretation is strongly supported by corresponding changes in the heats of adsorption with time. Calorimetry clearly indicates that when very large amounts of phosphate are added, new and very reactive surfaces are progressively exposed.

More phosphate was adsorbed when the soil was acid and when the soil contained less organic matter.
COPPER ADSORPTION BY ALKALINE SOILS
Authors: DHILLON S. K. , SIDHU P. S. , SINHA M. K.
Published: July 2006

The adsorption of copper by four alkaline soils of northwest India was investigated using 0.05m CaCI2 as supporting electrolyte. The adsorption data conformed to the competitive Langmuir adsorption equation although there was possibliity of copper hydroxide or carbonate precipitation at higher concentrations of added copper. The adsorption capacities of soils were related to CEC, clay content and CaCO3 equivalent of soil. The free energy changes for adsorption and for interaction were negative and positive respectively.
THE 40K and 214BI (FROM 238U) CONTENTS OF ROTHAMSTED SOILS DETERMINED BY GAMMA SPECTROMETRY
Authors: SMITH G. J. , TALIBUDEEN O.
Published: July 2006

The gamma spectra of 17 surface soils from the Rothamsted Classical Experiments, selected for contrasting potassium and phosphate fertiliser treatments, were obtained to measure their contents of K and 214Bi (from 238U accumulated from phosphate fertilisers) contents, using the 40K and 214Bi photopeaks. The fate of the fertiliser residues are discussed for each Experiment, related to differences in fertiliser treatment and period of application. In 1978, potassium fertilisers increased soil K content by about 20% in Hoosfield (since 1852) and Barnfield (since 1843), and by about 7% in Broadbalk (since 1843). The K contents of the P and PNaMg plots in Barnfield suggest that Na substituted significantly for K in crop uptake. In Hoosfield and Barnfield (except the PK and PNaMg plots) phosphate fertilisers increased 2l4Bi contents, but did not affect it in Broadbalk.

A new method for the quantitative determination of the content of any radionuclide emitting gamma radiation, and whose photopeak can be clearly resolved in the gamma spectrum of the soil, is described. This involves measurements on the soil and on the calibration samples containing radionuclides other than those to be assayed, using the same ‘sample:detector’ geometry, and the establishment of a calibration curve with reference sources in an energy range suitable for interpolating the results for the energy of the radionuclide. The values thus obtained are shown to compare very favourably with a direct method in which standards containing various amounts of the test radionuclide are used to calibrate the equipment. By using 1 kg samples of < 2 mm soil non‐destructively, both methods avoid sampling errors and the need for finely ground (< 0.15 mm) soil inherent in conventional chemical analysis.
THE KINETICS OF STRAW DECOMPOSITION IN RELATION TO ITS POTENTIAL TO PRODUCE THE PHYTOTOXIN ACETIC ACID
Authors: HARPER S. H. T. , LYNCH J. M.
Published: July 2006

The losses of total weight and of the individual components of oat straw were followed under field conditions over one cropping season. Decomposition rates of cellulose and hemicellulose were closely similar, and together these polysaccharides accounted for most of the weight losses. Losses of lignin were small, and total weight loss can be calculated from the increase in percentage lignin in recovered samples. Straw retained the potential to produce phytotoxic concentrations of acetic acid only during the early stages of decomposition. Both the water soluble components and the readily available polysaccharides are probably substrates for the production of acetic acid. Early incorporation of straw minimised the potential for toxin production during winter.
SOIL KAOLINS AND THEIR GENETIC RELATIONSHIPS IN SOUTHEAST QUEENSLAND, AUSTRALIA
Authors: KOPPI A. J. , SKJEMSTAD J. O.
Published: July 2006

Kaolin clays from soils in southeast Queensland give diffraction patterns which vary, particularly in the shape and position of the 00l reflections. To identify reasons for this variability, the kaolins in samples from forty soils were analysed for type, crystallinity, crystal size, and interstratification. Instrumental techniques used include X‐ray diffraction, infrared spectroscopy, and electron microscopy. Tiron‐extractable material was also determined.

Properties of the clays are related to factors of soil formation; poor crystallinity of the kaolin and different amounts of Tiron‐extractable material are related to parent material. Kaolin of very small particle size (<0. 1 μm), is the main cause of broad 00l peaks and high basal spacing.
Thermodynamics of K‐Ni and Ca‐Ni exchange reactions on kaolinite clay
Authors: BANSAL O. P.
Published: July 2006

Exchange equilibria involving nickel ions on potassium and calcium kaolinites were studied using exchange isotherms and derived thermodynamic parameters. The equilibrium was attained within 3 h and maximum adsorption occurred at pH 5.5. The exchange at pH 5.5 and an equilibrium time of 3 h yielded isotherms, equilibrium constants and standard fne energy values indicating a higher preference for nickel ions on the kaolinite surface. A stronger binding of nickel ions on the kaolinite surface was suggested by the enthalpy changes and the entropy changes indicate an increase in order of the system which may be due to changes in hydration states of nickel, potassium and calcium ions. The surface‐phase activity coefficients of the cations showed that with increasing nickel saturation, in the Ca‐Ni system fNi continuously increased while fCa decreased; in the K‐Ni system fK first increased and then decreased while fNi first decreased and then increasad, which may be attributed to differences in the distribution of ions in the Gouy‐Stem layer. The excess thermodynamic functions showed that the exchange reactions were non‐ideal: that is the mixture of cations oh the kaolinite surface was more stable and more tightly bound than the homo‐ionic forms.
Effect of barley plants on the decomposition of 14C‐labelled soil organic matter
Authors: SPARLING G. P. , CHESHIRE M. V. , MUNDIE C. M.
Published: July 2006

The effect of barley plants on the rate of decomposition of soil organic matter over a 6‐week period was studied using soil that had been previously labelled by incubation with 14C‐labelled ryegrass for 1 year. The plants reduced the loss of 14CO2, from soil by 70 per cent over 42 days. About half of the reduction was accounted for by the uptake of labelled C by the plant roots, very little 14C label being associated with the shoot. Chemical fractionation of the root showed that the 14C was chemically incorporated into cell wall materials such as cellulose and holocellulose. The reduction in organic matter decomposition in the presence of plants has been explained by earlier workers in terms ofa reduction in microbial activity as a result of a soil moisture deficit caused by plant transpiration. This explanation does not account for all the reduction in decomposition noted in the present experiments. Control soil (without a plant, but amended with glucose or

yeast extract to simulate the effect of root exudates) showed a small positive priming effect, the release of 14CO2, being increased. Thus the mechanism by which plants conserve organic matter is complex and cannot be explained merely by analogy to an increased level of nutrients available for microbial metabolism.
Effects of acetylene on nitrification and denitrification in two soils during incubation with ammonium nitrate
Authors: RYDEN J. C.
Published: July 2006

A loam from the Frilsham and one from the Wickham Series were incubated at 50 and 90 per cent of their water contents at saturation with 100 μg NH4NO3‐Ng−1 soil in the presence and absence of C2H2 (0.5 per cent, v/v). Acetylene inhibited nitrification in both soils, but had no effect on mineralization of N. No denitrification (measured as the production of N2O in the presence of C2H2) occurred during incubation at 50 per cent saturation. At 90 per cent saturation, denitrification resulted in a loss of 28.4 and 36.7 μg Ng−1 after 48 h from the Frilsham and Wickham soils, respectively. The concurrent inhibition of nitrification had no effect on the extent of denitrification at this time. In the Wickham soil, NO3− was exhausted after 168 h incubation in the presence of C2H2 and denitrification was underestimated by 13 μg Ng−. The data suggested that concurrent inhibition of nitrification during measurement of denitrification using the C2H2 inhibition technique is most likely to affect the estimate of denitrification loss when NO3−supply is limited by the inhibition of nitrification.
The use of land form‐soil associations in irrigation soil surveys in northern Nigeria
Authors: CHARTRES C. J.
Published: July 2006

The problems of soil mapping for irrigated agriculture on the savanna landscapes near Kano are discussed. Using data from a detailed soil survey, the possibility of establishing the major variations in soil properties relevant to irrigation by landform‐soil association mapping is considered. In the landform classes identified, some soil textural and colour properties have within‐class variances somewhat lower than their between‐class variances, and moderate interclass correlations. The magnitude of the between‐class differences in these properties is great enough to indicate whether the soils can be irrigated successfully and to help determine the irrigation method. Other soil properties including infiltration rate and topsoil available water capacity also differ significantly between landform classes, but their within‐class variabdity is still relatively high, indicating the need for further investigations. The variability of most soil chemical properties across the area is not successfully accounted for by landform‐soil association mapping. The results suggest that landform‐soil association mapping can be a useful means of establishing imgability a feasibility survey level.
Predicting bare soil temperature. III. Extension to single‐day variation
Authors: BUCHAN G. D.
Published: July 2006

The theory developed earlier to describe the averaged diurnal wave of bare soil temperature for a many‐day interval is extended to single‐day variation. This gives a new analytic model for the soil thermal ‘weather’(as opposed to ‘climate’) under typical temperate seedbed conditions, with input meteorological data in standard time‐series form. The model incorporates (i) a ‘ramp’ term to account for overall linear ascent or descent (i.e. non‐cyclic change) in the surface temperature, TO; and (ii) the actual initial condition, θ(z), of the temperature profile, which expresses its effect through a transient term. Soil temperature T(z, t) thus has three distinct components‐periodic, ramp, and transient.

The model is tested against data from a field site for I day each in spring and autumn.
Relationship between the decreases in soil stability effected by the growth of maize roots and changes in organically bound iron and aluminium
Authors: REID J. B. , GOSS M. J. , ROBERTSON P. D.
Published: July 2006

The growth of maize roots decreased fresh soil aggregate stability. Chemical pretreatment with sodium periodate (to assess the importance of polysaccharides) and acetylacetone (to assess the importance of organically bound Fe and Al) before measuring stability suggested that destruction of (organic matter)‐(Fe or Al)‐(mineral particle) linkages largely accounts for the effect. Removal of the Fe and Al cations by chelating agents released in the rhizosphere is the most likely mechanism. Changes in soil particle size distribution and the concentrations of water‐extractable cations around maize roots did not appear to be implicated.

Concentrations of water‐extractable Mg and K were sometimes greater in fresh soil which had supported maize than in fallow controls, which may reflect both release of bicarbonate or organic anions by the roots and the slaking of aggregates, reducing stability of the fresh maize soils.
The potentiometric measurement of stability constants of soil polycar boxy late‐Cu2+ chelates
Authors: YOUNG S. D. , BACHE B. W. , LINEMAN D. J.
Published: July 2006

Stability constants describing Cu2+ combination with three natural and one synthetic polycarboxylates were calculated from pH measurements alone, and using a Cu2+ ion selective electrode. Good agreement between the two methods justified the theory for polymer‐cation association. The results were consistent with the formation of a single complex CuL2 over a fairly wide range of metal‐ligand (L) ratios. The stability constant (βHCu) that was independent of polymer charge allowed the prediction of copper speciation in soil solution as a function of pH and soluble organic matter.
High gradient magnetic separation of some soil clays from Nigeria, Brazil and Colombia.
Authors: HUGHES J. C. , LE MARE P. H.
Published: July 2006

Phosphate sorption characteristics of the tropical soil clays described in Part I were determined. Estimates of native labile phosphate in the clays were similar to those calculated from whole soil data but under similar experimental conditions clays tended to sorb more exchangeable and less non‐exchangeable phosphate than whole soils. This may imply that short‐term measurements in soil underestimate the proportion of added phosphate that is labile and hence underestimate potential residual responses to fertilizer.

Relationships of sorbed phosphate with iron (Feox) and aluminium (Alox) extracted by acid‐ammonium oxalate and with carbon differed between clays from Nigerian soils and those from South America. Exchangeable phosphate was related to Alox in both groups and to Feox in the Nigerian clays. In both groups of clays non‐exchangeable phosphate was related positively to Alox but its relationship with carbon was negative in the South American clays and positive in those from Nigeria. These relationships are compared with those in whole soils in which the ratio of metal to carbon in organic‐metal complexes is important.
Microscopical aspects of garnet weathering in a humid tropical environment
Authors: EMBRECHTS J. , STOOPS G.
Published: July 2006

A sequence of different weathering stages of garnet under humid tropical conditions (Yaounde area, Cameroon) is described micromorphologically and mineralogically. The fissures, already observed in ‘fresh’ garnet in the rock, increase in number and size in the saprolite, and tend to get filled with well crystallized goethite. In this way a boxwork structure is formed. The isolated garnet fragments undergo a congruent dissolution, and the created space may be filled by gibbsite and/or globular Fe‐oxihydrates. In the A and B horizons a further dissolution of garnet and gibbsite takes place and all available space is filled with microcrystalline Fe‐oxihydrates. In this way a nodule, pseudomorph after garnet and with still recognizable boxwork‐structure, is formed. Near the soil surface these nodules may be transformed to haematite and/or undergo physical decay.

Fresh garnets entering directly into the soil environment mainly undergo a physical decay and transformation to amorphous or microcrystalline Fe‐oxihydrates, without formation of a pseudomorph.
Modification of soil physical properties by addition of Fe (III) polycations: influence on plant growth
Authors: SHANMUGANATHAN R. T. , OADES J. M.
Published: July 2006

The addition of 0.07 per cent Fe or more in the form of polycations decreased the total area of cracks and increased the number of transmissive pores of soils after simulated rainfall and drying. This resulted in increased per cent emergence and lower mean day of emergence of wheat plants. Per cent emergence (.v) was negatively correlated with penetrometer resistance (x).

The increased germination was followed by greater plant growth, including increased plant height and yield. The Fe polycation treatments had no significant effect on root length measured at harvest.
Variability of selected soil micronutrients in a single soil series in Berkshire, England
Authors: KHAN MOHAMMAD AFZAL , NORTCLIFF STEPHEN
Published: July 2006

The spatial variability of the concentrations of readily extractable iron, manganese, copper and zinc was examined in three 1 ha grids in close proximity within a single soil series. Estimates are given for the number of samples required to reach predetermined levels of precision. There were large contrasts between the grids and between the micronutrients. Iron and manganese showed greatest spatial variability and hence require the largest sample sizes, copper and zinc are less spatially variable.
The contribution of physics to land drainage
Authors: YOUNGS E. G.
Published: July 2006

The physics of land drainage is developed from the application of Darey's law to the water movement produced as a result of the conditions at the boundaries of the groundwater region in a given drainage situation. The physical understanding of the groundwater problem so obtained allows land drainage to be considered as an engineering operation founded on rational scientific principles and allows recommendations to be made concerning the design of installations. However, for theory to be applied in many field situations, a greater understanding of the soil‐water physics of heterogeneous soils, of fissured soils and of swelling soils is required.
The nitrogen content of particle size fractions separated from peat and its rate of mineralization during incubation
Authors: WILLIAMS B. L.
Published: July 2006

Particle size fractions, varying from 5 to 0.005 mm, were separated from samples of several peat types using a wet sieving technique. In all types, nitrogen content of fractions increased as particle size decreased, the fine fractions (0.15–0.005 mm) accounting for around 43–64% of the total nitrogen. During incubation, fractions from two blanket peats showed a net release of mineral nitrogen, whereas those from raised bog peats were characterized, for the most part, by net immobilization. Amounts of mineral nitrogen released in fractions from any one peat after 28 days incubation at 30°C did not always correlate with either total nitrogen content or C:N ratio. However, better correlations between mineral nitrogen production and total N were obtained for fractions of similar particle size. The proportion of the total nitrogen that was mineralized tended to be higher in coarse fractions > 0.15 mm, blanket peats giving much higher values than samples from raised bogs. Carbon dioxide release also varied with particle size, being highest in large particles and fibres and least in the size range 0.15–0.5 mm. Smaller particles < 0.15 mm, gave intermediate values that were higher in blanket than in raised bog peat.
Geochemical mapping in Oxfordshire: a comparison of stream sediment and soil sampling
Authors: KINNIBURGH D. G. , BECKETT P. H. T.
Published: July 2006

352 stream sediments and 429 topsoils were sampled from 1000 km2 of SW Oxfordshire. These were analysed by direct reading emission spectrometry, and simple geochemical maps were prepared for ten elements (Ca, Sr, Ba, V, Cr, Mn, Fe, Co, Cu and Pb). The maps showed that (i) the unsmoothed data were very ‘noisy’, (ii) there was a weak overall similarity between stream sediment and soil maps for some elements (Ca, Cu, Fe, Mn, Sr and Co) but little if any for the others; and (iii) removing some of the short‐range (less than 3 km) variability from the data by smoothing increased the overall similarity in some cases, but not in others.

Stream sediment and soil maps based on a more detailed sampling (topsoil and subsoil) of the area covered by map sheet SP30 did not show better agreement. The stream sediment maps generally agreed better with the subsoil maps than with the topsoil maps. Of the elements studied, Ca consistently showed the best agreement between stream sediment maps and soils. The agreement shown by the other elements was variable and unpredictable so that stream sediment data are unlikely to be useful for predicting local element concentrations in soils of areas without mineralization such as Oxfordshire.
Chloride dispersion in packed columns during saturated steady flow
Authors: RAUNSØ JENS
Published: July 2006

Chloride transport was investigated in four columns packed with glass spheres, spheres of a cation exchange resin, a loamy sand and a sandy loam, respectively. Using step input, vertical downward flow and relatively high flow‐rates, 0.01 m KCl displaced water in the column packed with glass spheres, otherwise 3.33 × 10−4m CaCl2 displaced or was displaced by 3.33 × 10−3m CaCl2. The breakthrough curves of chloride were analysed to give dispersion coefficients and mobile volumes. It was found that (i) chloride exchanged between mobile and immobile region in the sandy loam, (ii) the dispersion coefficient (K) was linearly related to pore flow velocity (U) for the individual columns, and that (iii) the ratio of dispersivity (dK/dU) to median grain diameter increased with increasing standard deviation of the logarithmicnormal grain size distribution.
The self diffusion of sodium in a naturally aggregated soil
Authors: STAUNTON S. , NYE P. H.
Published: July 2006

The self diffusion coefficient, in a naturally aggregated soil, of a solute which exists in both liquid and sorbed phases, was measured using a pulse labelling technique. This technique could have given evidence of slow equilibration between the two phases, but none was found. The magnitude of the self diffusion coefficient indicated that the solute is mobile in the sorbed phase. The mobility in the sorbed phase is described by a ‘virtual mobile fraction’. Within the limits set by the heterogeneity of natural aggregates, this was independent of both the volumetric moisture content and the bulk density.
Measurements of aeration in waterlogged soils: some improvements of techniques and their application to experiments using lysimeters
Authors: BLACKWELL P. S.
Published: July 2006

The techniques of measuring oxygen concentrations, oxygen flux and redox potential have been adapted for use in lysimeters. The accuracy and precision of the measurements have been improved, as well as their convenience for use in the limited soil volume of lysimeters.

Concentrations of dissolved and gaseous oxygen are measured with a membrane covered polarographic electrode. The analysis is made on samples of air or solution carefully extracted from collection vessels permanently in the soil.

Oxygen flux is measured with bare platinum electrodes. Careful choice is made of effective voltage for the measurement of equilibrium oxygen related currents.

Redox potential is measured by the same platinum electrode and the reproducibility of measurements from permanently installed electrodes was assessed.

The effect of soil structure upon the three kinds of measurement was seen and attributed to differences between the volumes of soil sampled by the different instruments.
Estimation of microbial biomass and activity in soil using microcalorimetry
Authors: SPARLING G. P.
Published: July 2006

Relationships between the rate of heat output from soil, the rate of respiration and the soil microbial biomass were investigated for 25 soils from northern Britain. The rate of heat output, measured in a Calvet microcalorimeter at 22°C, correlated well with the rate of carbon dioxide respiration. The average amount of heat evolved per cm3 of gas respired. 21.1 J cm−3, suggests that the biomass metabolism was largely aerobic.

The rate of heat output per unit of total microbial biomass was remarkably uniform over a wide range of soils, but showed differences depending upon whether the soil had been stored or amended. Mineral soils that had been stored at 4°C had the lowest heat output, 12.0 mW g−1 biomass C, compared with a mean of 20.4 mW g−1 biomass C for freshly‐collected soils. Amendment with glucose (0.5% w/w) caused an immediate increase in respiration and heat output, up to 59.4 mW g−1 biomass C for stored soils and 188.2 mW g−1 biomass C for freshly collected soils.

There was a consistent relationship between the biomass and the rate of heat output from freshly collected and amended mineral and organic soils which gave a linear fit using log transformed data: y= 0.6970+ 1.025x (r= 0.98, P < 0.001) (y=log10 biomass C, μgC g−1; x=log10 rate of heat output at 22°C, μW g−1).

The overall relationship between biomass and the rate of heat output for all the amended samples was: 1 g biomass C= 180.05 ± 34.61 mW.
Hypothesis on the pedogenesis of the ‘gley podzols’ of the west coast of South Island, New Zealand
Authors: FARMER V. C. , MEW G. , CLAYDEN B. , LEE R.
Published: July 2006

The gley podzols of the west coast of South Island, New Zealand, typically exhibit permanent waterlogging extending from the surface to depths of 1–3 m. Their formation is explained by a continuation of processes which give rise to Peaty Podzols with thin iron pan (Ironpan Stagnopodzols; Placaquods). Iron pans initially formed within the upper B horizon are breached by acidic reducing waters and reform at a succession of lower levels down to 3 m or more below the surface.
Sampling and bulking strategies for estimating soil properties in small regions
Authors: WEBSTER R. , BURGESS T. M.
Published: July 2006

Estimates of mean values of soil properties within small rectangular blocks of land can be obtained by kriging provided the semi‐variogram is known. This paper describes optimal rectangular grid sampling configurations whereby estimation variances can be minimized. For linear semi‐variograms square blocks are best estimated by sampling at the nodes of a centrally placed grid with its interval equal to the block side divided by the square root of the sample size. For spherical semi‐variograms the same configuration is almost optimal. The estimation variance of a bulked sample can be identical with that of a kriged estimate where the semi‐variogram is linear and equal portions of soil are taken from each node on the optimally configured grid and provided the soil property is additive. For spherical semi‐variograms the above is approximately true. Comparisons with estimates that take no account of known spatial dependence show that the true variances can be much less than those apparent using classical theory, and the necessary sampling effort much less. Within block‐variances are often needed for planning, and an appendix gives two‐dimensional auxiliary functions from which they can be calculated for linear and spherical semi‐variograms.
A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on shallow soil overlying Chalk: crop uptake and leaching losses
Authors: DOWDELL R. J. , WEBSTER C. P. , HILL D. , MERCER E. R.
Published: July 2006

The objective of this work was to determine the fate of fertilizer nitrogen (labelled with nitrogen‐15) applied to an undisturbed shallow soil overlying Chalk contained in 10 lysimeters (80 cm diameter, 135 cm deep). Measurements are reported of the nitrogen uptake by four spring barley crops and the rate and extent of leaching of nitrate beyond the roots. The crops were fertilized with 0, 80 or 120 kg N ha−1 in each of four years, but only the first application in 1977 was labelled with nitrogen −15. Rainfall and irrigation approximated to the long‐term average, but in two treatments dry or wet spring conditions were imposed for the 10 weeks after sowing the first crop in 1977. The dry matter and grain yields of the spring barley crops varied from year to year in the ranges 8.7–14.0 t ha−1 and 3.5–6.1 t ha−1 respectively. The total nitrogen harvested in the crop approximated to the amount of nitrogen applied in each year with an apparent recovery of fertilizer in the range 38–76%. The recovery of nitrogen derived from fertilizer (labelled with nitrogen‐15) was 46–54% in the first crop and after 2 years rapidly declined to below 1%. The total amount of nitrogen‐15 labelled fertilizer recovered in four barley crops was 49–57% of that applied.

Mean annual nitrate concentrations in water draining from the base of the lysimeters were in the range 11.8–26.7 mg N 1−1 and did not differ significantly between nitrogen fertilizer treatments (0, 80 and 120 kg N ha−1 a−1). In all treatments nitrate concentrations varied considerably within each growing season, with a cycle of peaks and troughs. Annual losses of nitrate were in the range 39–128 kg N ha−1, and the mean annual losses over the 4 years varied between lysimeters from 65 to 83 kg N ha−1. Nitrogen‐15 labelled nitrate was detected in the first drainage water collected in autumn following its spring application, 5 months earlier. Recovery of fertilizer‐derived nitrogen in drainage water was greatest during the winter following the second barley crop, and was 3.4–3.7% of the nitrogen‐15 applied. Over the 4 years of the experiment 6.3–6.6% of labelled fertilizer was accounted for in drainage water, representing 2–3% of the total nitrogen lost by leaching.
Decomposition kinetics of straw saccharides and synthesis of microbial saccharides under field conditions
Authors: MURAYAMA S.
Published: July 2006

The decomposition of rice and barley straw saccharides under field conditions was well represented by the first‐order kinetics model of Yt=C1e−k1t+C2e−k2t, where Yt is the remaining amount at time t, k1 and k2 are the decomposition rate constants (time−1) for the labile fraction (C1) and the non‐labile fraction (C2), respectively. About 82% of the total saccharide content of the rice straw was in the labile fraction with a rate constant 0.64–0.81, the values for the barley straw being 70–92% and 0.50–0.61, respectively. The non‐labile fraction appeared to persist for a long time, with a half‐value period of 9–59 months. Barley straw and its saccharides decomposed at a slower rate than rice straw. Much more favourable initial decomposition was observed in a paddy field than in an upland field.

Mannose, fucose, rhamnose and ribose were synthesized in parallel with the flush of decomposition of straw saccharides.