摘要:

SUMMARYSome kaolinitic soils derived from basaltic material contain 2:1 minerals as a discrete phase and/or interstratified with kaolin as determined by X‐ray diffraction (XRD) and by chemical analysis of DCB‐treated clays, while others show little or no evidence of 2:1 minerals. Mineral impurities were not detected by electron diffraction in the latter group. There is good agreement between the interpretation of XRD traces and the SiO2/Al2O3ratio given by chemical analysis. Some kaolin is seen by electron microscopy to be of very small particle size, and two distinct morphological types have been recognized. High surface area measurements are consistent with fine particular size. These profiles contain kaolin with higher than normal CEC and permanent negative charges which cannot be accounted for by the presence of 2:1 clay minerals alone and which are attributed to a degree of isomorphous substitution. This substitution and/or mineral impurities may have limited kaolin crystal growth during neoformat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02274.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYFive soil pedons–two aquic and two udic Haplustalfs and one petrocalcic Natrustalf–from the Indo‐Gangetic alluvial plain of Western Uttar Pradesh were investigated to evaluate the pedogenetic processes. Sand/silt ratios indicate that parent material discontinuities are insignificant. Higher K content and lower SiO2/R2O3ratios of the non‐clay fractions in Bt, rather than in the A, horizons suggest maximum weathering at or near the surface.An almost linear relationship between decrease in molar SiO2/R2O3and % increase in clay to about 100cm depth in all the pedons, presence of clay argillans in Bt horizons (where % clay, fine/coarse clay ratio and bulk density values are greatest), all indicate that the development of argillic horizons in these soils was due, at least partly, to lessivage of clay. Fe in clay fractions decreases with depth whilst Al increases, but in the fine earth both increase steadily with depth. This, together with crystalline iron concretions in the lower Bt horizons, suggests that in Haplustalfs these horizons are gaining clay by neoformation/ reorganization of illuviated constituents, especiall

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02275.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYA method for the analysis of NO3‐N in a 2mKCL soil extract, using ion chromatography, is discussed. It involves the treatment of the KCl extract with Ag+‐activated cation exchange resin to remove excess Cl–, followed by analysis using a Dionex ion chromatograph. The results of NO3‐N in soil extracts agreed closely with those obtained by steam distillation. The method was linear up to 20 mg N dm–3with a detection limit of 0.1 mg Ndm–3. Quantitative recovery of NO3‐N added to soil extracts over the linear range were observed.Standard deviations of samples containing 2.57 and 15.11 mgN dm–3were found to be 0.06 and 0.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02276.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYSoil samples taken by soil auger to a depth of 150 mm from randomly selected agricultural fields throughout England and Wales were analysed for total As, B, Cd, Co, Cr, Cu, Hg, Ni, Pb, Se and Zn, acetic acid‐extractable Cd, Co, Cu, Ni, Pb and Zn, EDTA‐extractable Cd, Co, Cu, Ni, Pb, Se and Zn, ammonium oxalate extractable Ni and Mo and hot water‐extractable B. Median, log‐derived mean and range data are given for each element. Median values are given also by parent material and textural g

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02277.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAn important factor in plant availability of copper is its anomalous binding to soil humic substances, for which aggregation phenomena have been implicated. Two alternative models of copper‐induced humate aggregation are theoretically explored to characterize binding behaviour. In the first model the copper modifies the humic acid so that it self‐associates indefinitely. Copper binding is found to be dramatically enhanced, except at the very low concentrations corresponding to copper‐deficiency. In the second model bivalent copper forms bridges between different humate molecules to yield an array of large cross‐linked complexes. In the latter cross‐linking model, binding of copper is markedly enhanced at low copper concentrations, a behaviour still found when only relatively few sites sterically permit cross‐linking. The cross‐linking model accounts, at least in part, for the low availability and immobility of copper in some problem soils and is consistent with several items of experime

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02278.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe cation composition of solutions and leachates from small‐diameter laboratory soil columns was examined over a 23‐week period after the addition of lime (0, 3 and 6 t ha–1) and/or nitrogen fertilizer (0 or 200 kg N ha–1) to an acid soil (pH 4.2). Water was applied at regular intervals to the surface of the columns and 17 leachate samples collected. Initially, the pH of the leachate was high (6.6) in all treatments (including those without lime) but fell rapidly to approach a steady value of 3.8. Large losses of calcium occurred from all columns; the total equivalent amounts of lime lost ranged from 0.88 (no addition) to 2.38 (with added lime) t CaCO3ha–1High concentrations of aluminium (181–325 μM) were present in leachates from all treatments; the addition of 200 kg N ha–1increased the leaching of Al by 94%; addition of lime also increased the amounts of Al leached (by 52%).The pH of the soil solution (separated by centrifugation) was influenced by treatment, especially in the top 0–40 mm of the column. Aluminium concentration was related to pH, but the form of the relationship differed amongs

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02279.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYZinc sorption curves were obtained after treatment of a soil with several rates of phosphate and with two rates of lime. The lime permitted evaluation of the effects of phosphate on Zn sorption via its effects on pH. The phosphate was either incubated with the soil at a high temperature before reaction with Zn or was supplied at the same time as the Zn. This produced treatments with similar concentration of phosphate in solution but different amounts of sorbed phosphate.Two distinct effects of phosphate addition on Zn sorption were detected. One arose from effects of phosphate on pH. This effect could be large and could either increase or decrease Zn sorption depending on the direction of the pH effect. A second effect was correlated with the amount of sorbed phosphate and was assumed to operate through the effects of phosphate on charge. The effects were small at low levels of Zn but larger at higher levels. This suggested that Zn and phosphate were sorbed at opposite ends of a spectrum of electrostatic potentials and overlap only occurred when the level of application was high. A third possible effect, due to reaction of the soil with zinc phosphate complexes in solution, was not proved.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02280.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYTo characterize the fabric of a wet soil sample two sets of experiments were performed. In one, water retention and shrinkage curves were determined with samples stored at the field water content, and in the other, pore size distribution curves and microscopic observations were made as samples progressively dried. The experiments were performed with soil samples of different aggregate sizes to determine the contribution of each class of pores to porosity.Data were analysed by comparing (i) the amount of water extracted from the sample, (ii) the air‐filled porosity of the sample and (iii) the accumulated pore volume by mercury injection, each in relation to the equivalent pore radius. This gives information on the geometry of pores developed during the drying process. It has shown that micrometric cracks in dried soils are not artefacts but the result of a more severe drying never reached by the material in the fiel

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02281.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYAutumnal recharge of water in a clay soil is prolonged, taking>3 months. Once thoroughly re‐wetted, mean winter water contents lie within 0.5% v/v year by year at each site, and variability during the winter period is low, with SE = 0.2%. The uniformity of winter soil water content reflects the important part played by macropores as rapid transmission pathways for the disposal of rainwater. Weekly changes in water content are small but are inversely related to antecedent levels and the soil may become marginally drier from one week to the next despite substantial falls of rain if the soil begins the period at moisture contents higher than the seasonal mean. This behaviour has been observed in other clays and in lighter textured soils. The constancy of the mean winter soil water content provides a practical measure of the upper limit of plant‐available water, i.e. field capacity. It can be established by field sampling on as few as six occasions, and is free from the problems associated with plot irrigation and tension table methods of determining field capac

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02282.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

SUMMARYThe two‐parameter model In φ= a+b ln θis widely accepted in the literature as providing a good fit to the soil moisture characteristic for a wide variety of soil types. This model is examined and it is shown that the parametersaandbare not independent, and hence that the SMC may be represented by a one‐parameter model with little loss of accuracy. Thus it is possible to define the SMC from one paired measurement of soil water content against potential. Because this single paired measurement is all that is required it also avoids the necessity of classification of the soil type–indeed it may provide an additional means of soil identif

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1987.tb02283.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY