bluuebunny/crossref_metadata_2025_split huggingface dataset:
THE DISTRIBUTION OF LABELLED SUGARS IN SOIL PARTICLE SIZE FRACTIONS AS A MEANS OF DISTINGUISHING PLANT AND MICROBIAL CARBOHYDRATE RESIDUES
Authors: CHESHIRE M. V. , MUNDIE C. M. 
Published: July 2006

SummarySoils of the Countesswells and Insch series incubated with 14C labelled glucose or plant materials have been separated into clay (< 2 μm), silt, (2–20 μm), fine sand (20–250 μm) and coarse sand (>250μm) fractions and the distribution of individual labelled and unlabelled sugars was determined in each fraction.Both soils contained about 10–15 per cent clay, 18–23 per cent silt and about 60 per cent fine and coarse sand. For all soil samples the concentrations of sugars were usually greatest in the clay, slightly less in the silt, with values in the sand fractions being five or ten times lower, except when fresh plant material was present.In 14C glucose amended Insch soil, 55 per cent of the radioactivity in sugars (predominantly hexoses) occurred in the clay, 36 per cent in the silt, 3 per cent in the fine sand and 6 per cent in the coarse sand after 28 days incubation. For the Countesswells soil the values were 55, 42, 2 and 1 per cent respectively. In 14C ryegrass amended soil before incubation. 77 per cent of the radioactivity in sugars (predominantly glucose, arabinose and xylose) was in the coarse sand. After one year's incubation this had fallen to 59 per cent. In soil amended with 14C cereal rye straw the distribution of radioactivity in sugars after four years incubation was: clay, 21 per cent; silt, 43 per cent; fine sand, 21 per cent; coarse sand, 4 per cent.These distributions were compared with that of the naturally occurring sugars: clay, 31–42 per cent; silt, 40–43 per cent; fine sand, 3–11 per cent; coarse sand, 12–20 per cent.
The measurement of the variation with depth of the hydraulic conductivity of saturated soil monoliths
Authors: YOUNGS E.G. 
Published: July 2006

SummaryHydraulic conductivity profiles of saturated composite porous columns were obtained in two ways: first, from measurements of the hydraulic potential profiles with uniform vertical flow; and second, by making use of a potential theorem concerning the flow between sources and sinks, from measurements of the hydraulic potential difference between the ponded surface and the base when the flow was intercepted in turn by successive drains located at intervals down the column. Both techniques gave the same results. The hydraulic conductivity profile of a structurally unstable column changed significantly with time, suggesting that such measurements might be used to monitor soil structural changes and root development in lysimeter studies.
Trimethylsilylation of commonly occurring primary and secondary minerals in soils
Authors: SMITH B. F. L. , PATERSON E. , MITCHELL B. D. 
Published: July 2006

SummarySoil is formed through the weathering of minerals—mainly silicates—and the manner in which these materials weather is related to some extent to the arrangement of silica units within their structures. This has been termed the degree of polymerizafion of the silica and can be quantitatively assessed by preparing organic (trimethylsilyl) derivatives which can be separated and identified. This procedure has been applied to a number of primary and secondary (including clay and highly disordered) minerals occurring in soils and has indicated that: (a) of the primary minerals, the ferro‐magnesian are the most susceptible to acid attack; (b) inorganic gels, particularly those high in alumina, are reactive; and (c) crystalline clay minerals, especially kaolinite and illite, are relatively stable.
Composition and development of some soils on glauconitic Cretaceous (Upper Greensand) rocks in southern England
Authors: LOVELAND P. J. , FINDLAY D. C. 
Published: July 2006

SummaryThree soils developed in glauconitic parent materials and differing in water regime have been examined. Particle size distribution and mineralogical data show them to be free of additions of extraneous material and major lithological discontinuities. The principal soil‐forming processes have been physical disaggregation of glauconite grains, translocation of clay, removal of Fe II from the glauconite structure due to charge imbalance following loss of structural K, and oxidation of this Fe II to form hydrous Fe oxides. A randomly interstratified illit‐mectite has also formed by weathering of the glauconite. The evidence of void argillan formation at considerable depth in the coarser textured soils is difficult to reconcile with conventional ideas regarding the formation of such features. The glauconite in these soil parent materials has an unusually low Fe II content, which confers considerable stability on the glauconite surface. As a consequence, the glauconite in these soils is relatively resistant to weathering.
Soil water behaviour in response to changes in soil structure
Authors: HAMBLIN A. P. 
Published: July 2006

SummarySurface horizons of two Australian alfisols which had been cropped for 3 years to wheat by zero, minimum and ploughed tillage were compared for differences in structure. Total porosities and pore size distributions differed between treatments, but values for water and air permeability, sorptivity, diffusivity and evaporation rate were not necessarily ranked in the same order. The stability of soil structure was usefully described by the ratio of water to air permeability (kw/ka), which indicated the relatively fragile nature of the ploughed structures, despite their initially greater proportion of coarse porosity. Time of sampling after seeding also influenced hydraulic properties which were found to vary significantly over a 10‐week period. Variations in vertical distribution of organic matter between tillage treatments is postulated as influencing the differences in structural stability.
Suppression of decomposition of 14C‐labelled plant roots in the presence of living roots of maize and perennial ryegrass
Authors: REID J. B. , GOSS M. J. 
Published: July 2006

SummaryThe rates of decomposition of barley roots labelled with 14C were investigated in soil planted with maize or perennial ryegrass and in fallow controls. Evolution of 14CO2 was significantly less from the planted soils than from fallow controls.Roots of maize and ryegrass appeared to compete substantially with soil microbes for 14C‐labelled materials. Simple competitive effects were, however, insufficient to explain all of the observed effects of root growth on soil organic matter decomposition.There was no indication that the detrimental effects of maize roots on aggregate stability could be associated with increased degradation of native soil organic materials; the broader significance of the results is also discussed.
Soil physical conditions on reclaimed colliery spoil heaps
Authors: RIMMER D. L. 
Published: July 2006

SummarySoil physical conditions are inherently poor and lead to summer droughtiness and winter waterlogging on many spoil heaps. The high stone content makes soil physical measurement difficult. The development of appropriate field and laboratory methods, which allow the calculation of sample composition, bulk density, total porosity, air‐ and water‐filled porosities and available water capacity are described.A survey of 12 reclaimed colliery spoil heaps of varying age showed that, apart from an increase in organic matter in the surface layer (0–5 cm) with increasing age of site, there were no consistent trends with age and this is attributed to initial between‐site variability. General trends with depth down the profile to 30 cm were obtained by combining the data from all 12 sites. With increasing depth the bulk density increased and the porosity decreased. A higher porosity in the 0–5 cm layer was associated with (i) lower stone content (>2 mm) due to weathering and (ii) organic matter accumulation. In the subsurface layers (>5 cm) the stone content was essentially constant and the decreasing porosity with depth is explained as being due to settling. Overall there was a strong negative correlation between porosity of samples and stone content, which in turn was determined by the weatherability of the material.
Changes in soil aggregate water stability induced by wetting and drying cycles in non‐saturated soil
Authors: UTOMO W. H. , DEXTER A. R. 
Published: July 2006

SummaryWetting and drying of remoulded soil resulted in water stable aggregation. The greatest proportions of water stable aggregates arose from wetting and drying in the −1 to −100 kPa range of matric water potential. The effect occurred with sterile and non‐sterile soil. but the proportion of water stable aggregates was less with sterile soil.The application of wetting and drying cycles in the laboratory to non‐tilled soil resulted in a steady decrease in the proportion of water stable aggregates. With tilled soil, the proportion of water stable aggregates first increased to a maximum and then decreased steadily with further wetting and drying cycles. However. with sterilized, tilled soil, only a steady decrease in the proportion of water stable aggregates was observed.Natural water content fluctuations in the field after tillage gave an increase in water stability to a maximum after a few days followed by a steady decrease. The similarity of this result to that obtained in the laboratory for tilled. non‐sterilized soil indicates that micro‐organisms were probably contributing to the observed short‐term changes in the water stability of aggregates in the field.
A comparative study of three methods of water removal prior to resin impregnation of two soils
Authors: MURPHY C. P. 
Published: July 2006

SummaryThe water in replicate samples from sub‐surface horizons of a clayey and a fine‐silty soil was removed either by oven‐drying, freeze‐drying or by acetone‐replacement prior to resin impregnation. Pore space photograms (pores >60 μm diam.) from thin sections were analysed on a Quantimet 720 image analysing computer following each drying technique. During oven‐ and freeze‐drying the clayey soil contracted considerably and subsequently satisfactory impregnation of these samples was either difficult or impossible. This macro‐shrinkage caused a decrease in number and lengths of most planar pores and a decrease in size and number of all intra‐aggregate pores. The loss in pore space and continuity obviously affected resin impregnation. The clayey samples in which water was replaced by acetone, and all samples of the silty soil, however pretreated, showed no measurable macro‐shrinkage and all impregnated well. Oven‐drying the silty soil appears to increase the porosity, causing an increase in size of all pores. A mechanism for this apparent enlargement is proposed. It is evident that acetone‐replacement of the soil water prior to resin impregnation is the best of the three methods used here and should be seriously considered when image analysis is to be carried out on resin‐impregnated blocks from soils of similar or related textures.
Pyrite and siderite oxidation in swamp sediments
Authors: POSTMA DIEKE 
Published: July 2006

SummaryDifferences in the processes of pyrite and siderite oxidation, in reclaimed swamp sediments of the Skjernå delta (Denmark), are described from sediment chemistry, mineralogy and pore water chemistry.Pyrite oxidation leads to extreme soil acidification, with pH dropping to about 2, the release of large amounts of weathering products to the pore water, and the precipitation ofiron oxides, jarosite and gypsum.Siderite oxidation results only in moderate soil acidification where the pH does not drop below 3.5, while part of the acidification is due to the oxidation of small amounts of sulphur compounds together with siderite. The release of weathering products to the pore water is limited and only iron oxide is precipitated.Calculations indicate that equilibrium with amorphous FeOOH, gypsum and amorphous Al(OH)3 sets an upper limit to the Fe3+, SO4 and Al concentrations in the pore water.
Gas diffusion through soil crumbs: the effects of wetting and swelling
Authors: CURRIE J. A. 
Published: July 2006

SummaryGas diffusion coefficients for hydrogen through air in packings of 1–2 mm crumbs from a clay loam (both under grass and under arable) and from a sandy loam were measured over a range of water contents as the soils were wetted. Diffusion coefficients decreased with increasing water content (decreasing air content) in three stages: in the first, to specific water contents of 0.08–0.10 gg1, decreases were small indicating the filling of pores less effective for diffusion; in the second, to crumb saturation, decreases were greater, and in the third, to complete saturation, decreases were greatest. Two of these stages are related to swelling: in the first, any slight swelling is contained within the crumb and there is loss to the gas of crumb pores only; in the second, the crumbs swell and there is simultaneous loss of crumb pore space and, more important, inter‐crumb space; in the third, swelling is complete, so, as in nonswelling soil, there is loss of inter‐crumb space only. Pore size and pore shape in the three soils, and pore distribution (intra‐crumb structure) in the grassland clay loam, may also affect diffusion but to a lesser extent: these influences are discussed. On subsequent drying there was little evidence of hysteresis in diffusion with water content, and only a slight indication in the arable clay loam of decreases due to structural degradation during the measurements.
A field study of effects of contrasting methods of cultivation on soil nitrate content during autumn, winter and spring
Authors: DOWDELL R. J. , CREES R. , CANNELL R. Q. 
Published: July 2006

SummaryThe nitrate content of three heavy clay soils (Evesham, Denchworth and Lawford series) was examined after direct drilling or ploughing, and of another clay soil (Denchworth series) with or without mole drainage and after tine cultivation. Autumn‐sown crops were grown at all these sites during the years 1973–80. Except in 1974–75, the nitrate concentration of the soil solution sampled from direct‐drilled plots was less than from the ploughed plots, particularly in late autumn and early winter. By January the plots which had been ploughed contained 12–65 kg N ha−1 more mineral nitrogen than direct‐drilled plots, but differences between cultivation treatments disappeared rapidly and had gone by early March. After tine cultivation, the nitrate content of the soil profile was not affected by the contrasting drainage status of the plots with or without mole drainage. These results support the view that although denitrification can be greater in direct‐drilled soil, the larger nitrate concentrations present in ploughed soil result from the soil disturbance exposing less accessible substrates to mineralization by microbes. By this means, considerable amounts of mineral nitrogen are made available at the beginning of the winter, during the establishment of autumn‐sown crops.
Water and oxygen regimes of four soil types at Newcastleton Forest, south Scotland
Authors: PYATT D. G. , SMITH K. A. 
Published: July 2006

SummaryThe water and oxygen status of four upland soils under Sitka spruce plantations was studied for 2 years. In a brown earth, waterlogging only occurred ephemerally in the subsoil and oxgen concentrations were generally high. In contrast, waterlogged and near‐anaerobic conditions persisted for much of the year in stagnogley and stagnohumic gley soils. In a peaty stagnopodzol moist conditions occurred above and below the thin ironpan, but while high oxygen concentrations generally persisted in the subsoil, low concentrations were common in the soil above. In the brown earth, healthy roots of Sitka spruce were present at a depth of 85 cm, but in the gley soils rooting was mainly limited to 25 cm and many roots were dead. In the peaty stagnopodzol, roots penetrated the ironpan and grew in the subsoil to 75 cm depth.
Fulvic acids: structure and metal binding. I. A random molecular model
Authors: MURRAY K. , LINDER P. W. 
Published: July 2006

SummaryWe have investigated a model of fulvic acid based on randomized positioning of functional groups and aromatic rings which can be used to deduce the types of metal chelating sites and provide statistical estimates of their concentrations. A FORTRAN program ‘RANDOM’ has been written which generates random molecules of fulvic acid. For each molecule generated the program also searches for and counts 14 types of binding site and calculates average concentrations over one thousand such molecules. A formula relating percentage aromatic carbon to the molar hydrogen/carbon ratio is also derived. The results show that the predominant bidentate sites are likely to be phthalate‐ and salicylate‐type sites with a significant proportion of aromatic carboxyl and phenolic hydroxyl not participating in chelating sites.
Diffusion coefficients of nitrate, chloride, sulphate and water in cracked and uncracked Chalk
Authors: HILL D. 
Published: July 2006

SUMMARYThe rates of diffusion of chloride, sulphate and water, labelled respectively with 36Cl, 35S and 3H, and unlabelled nitrate, were measured in small cylindrical Chalk monoliths. Using a simple mathematical model, diffusion coefficients were calculated to provide a basis for comparing the movement of these substances through Chalk rock in the absence of hydrostatic pressure gradients. The diffusion coefficients of chloride and nitrate were similar, with a range of values (0.52–3.23 × 10−6 cm2 s−1) and (0.53–3.20 × 10−6 cm2 s−1) respectively. These were slightly less than for tritiated water (0.60–3.51 × 10−6 cm2 s−1), while the coefficient for sulphate was about half that of the others (0.28–1.47 × 10−6 cm2 s−1). The coefficients indicate the absence of any interaction with the Chalk surfaces.
Gel permeation chromatography studies on the speciation of lead in solutions of heavily polluted soils
Authors: GREGSON SUSANK. , ALLOWAY B. J. 
Published: July 2006

SUMMARYSamples of solutions from soils contaminated with lead as a result of three different processes: natural weathering and dispersion from an ore body, mining and smelting, and sewage sludge‐amendment to land, were fractionated on Sephadex gels. Solutions from the sludge‐amended soil, dried sludge and calcareous mine soils were found to contain a proportion of lead eluted at the exclusion limit of the gel, accompanied by a peak in U.V. absorbance, implying the occurrence of a high molecular weight organo‐lead complex. This fraction was proportionally highest in the solution from the dried sludge sample; however, low molecular weight organic peaks were also accompanied by elution of Pb in all samples except that from the low pH, naturally contaminated site. Association of Pb with organic matter was observed to be greater in samples of soil solution with a higher initial pH and this may be related to increased stability constants for Pb‐organo complexes at higher pH.
Highly weathered soils in the east coast hinterland of Southern Africa with thick, humus‐rich A1 horizons
Authors: MACVICAR C. N. , FITZPATRICK R. W. , SOBCZYK M. E. 
Published: July 2006

SUMMARYStrongly weathered red and yellow soils with thick (490–900 mm) humic Al horizons (Haplohumox and Palchumults) derived from sandstones and basic igneous rocks, and occurring near the east coast of Southern Africa, are described and discussed in terms of their distribution, morphology, texture, mineralogy, chemistry, genesis and classification. The high organic matter content (2–5%C) of the Al contributes significantly to a high pH‐dependent negative charge, probably to poorer crystallinity of goethite and kaolinite and to the transformation of haematite to goethite. Varying proportions of kaolinite and gibbsite reflect different soil ages within these old landscapes. The yellow colour of aluminous goethite, the main pedogenic iron oxide, is masked in the Al by organic matter and in red B2 horizons by haematite. Temperature may have influenced the broad pattern of occurrence of red and yellow B2 horizons. These soils need not, as previously suggested, have developed from the weathering products of an ancient laterite. Neither Soil Taxonomy nor the South African soil classification system accommodates the soils entirely satisfactorily and possible improvements to the latter are discussed.
A lysimeter study of the fate of fertilizer nitrogen in spring barley crops grown on a shallow soil overlying Chalk: denitrification losses and the nitrogen balance
Authors: DOWDELL R. J. , WEBSTER C. P. 
Published: July 2006

SUMMARYFour successive spring barley crops were grown in monoliths of a shallow soil overlying Chalk, contained in lysimeters. After harvest of the fourth crop, 25% of the nitrogen‐15 labelled fertilizer applied 4 years earlier was found remaining in the roots and soil. Of this, 73% was present in the upper 30cm of the profile. From the amounts of fertilizer derived nitrogen that remained at the beginning of each cropping season we estimate that 5–6% of the residual nitrogen‐15 turned over each year, representing a net release of 20% of the labelled nitrogen contained in the microbial biomass. Mineralization of the total biomass at the same fractional rate would release 120 kg N ha−1 a−1. This estimate is supported by the difference between input and outputs of total nitrogen during the experiment of 76–94 kg N ha−1 a−1 in fertilized lysimeters and 129kg N ha−1 a−1 in unfertilized control lysimeters. The total recovery of the applied labelled nitrogen was 81–87%. The nitrogen not accounted for was taken to be lost by denitrification of nitrate to dinitrogen, as no nitrous oxide emissions were detected during the experiment. Laboratory studies in aerobic and anaerobic conditions in presence of acetylene confirmed that 10–20% of the applied nitrogen‐15 could have been transformed to dinitrogen.
Modelling the effects of pH on phosphate sorption by soils
Authors: BARROW N. J. 
Published: July 2006

SUMMARYSamples of six soils were incubated at 60°C for 24 h with several levels of either calcium carbonate or hydrochloric acid. Phosphate sorption was then measured on sub‐samples of the treated soils over 24 h at 25°C. In one set of measurements on all soils, 0.01 M calcium chloride was used as the background electrolyte. In another set, on two soils, 0.01 M sodium chloride was used. An interpolation method was used to give points on the three‐dimensional surface relating the final pH of the suspensions to sorption of phosphate at specified solution concentrations of phosphate.The effects of pH on phosphate sorption differed between soils. For unfertilized soils, increases in pH up to about pH 5.5 decreased sorption. Further increases in pH decreased sorption further in one soil and increased it in three others. For fertilized soils, measured sorption increased with pH. When sodium chloride was used instead of calcium chloride, there was a more marked trend for sorption to decrease as pH increased.Differences between the soils were ascribed to differences in two soil properties. One was the rate at which the electrostatic potential in the plane of adsorption decreased as pH increased. Only small differences in the rate of change of potential were needed to reproduce the observed differences between soils. The electrostatic potential would decrease more quickly in solutions of a sodium salt than in solutions of a calcium salt and this explains the observed differences between these media. The other soil property that affected observed sorption was the release of phosphate from the soil. The amount released was largest at low pH. Consequently, for fertilized soils, measured sorption increased with pH.