摘要:

SummaryAerating pyritic soils causes acidification and the forrnation of acid sulphate soils, or cat‐clay. The Oxidation of pyrite in soils is associated with the deposition in tile drains of a form of ochre quite distinct from that formed by the action of filamentous iron bacteria. Pyrite‐derived ochre results from the action ofThiobacillus ferrooxidans, which, below pH 3.5–4.0, catalyses the Oxidation of Fe2+and pyrite. In soils less acid thanc.pH 4, pyrite oxidizes relatively slowly by chemical reactions to Fe2+and SO24−. Under these conditions iron enters the drains as Fe2+and is there oxidized byT. ferrooicidansand deposited as hydrated ferric oxide. Once the soil becomes acid enough forT. ferrooxidansto multiply, the rate at which pyrite oxidizes increases several‐fold, and atc.pH 3 iron appears in the drainage water in the ferric form. Liming seems to decrease the rate of

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01636.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThree 0.01mFe(ClO4)3Solutions ofR= 0, 1, and 2, respectively, were studied over a period of 8 months, whereRis referred to the HCO3−/Fe3+mole ratio in preparation. TheR= 0 solution was initially light yellow and clear but rapidly changed to a dense cloudy Suspension after a 9‐day induction period. Hydrolysed species rapidly grew from650 nm. Particles of intermediate size were not observed during the entire period of study. Settleable FeOOH precipi‐tate was first observed in 5 weeks with 23 per cent of its iron noted as precipitate at the end of 5 months. TheR= 1 andR= 2 Solutions were reddish‐brown of low turbidity. Rapid hydrolysis and polymerization were observed immediately after preparation. The hydrolysed species gradually grew in size during ageing and no settleable FeOOH precipitate was observed for at least two years. A hypo‐thesis based on Lamb and Jacques's model of Fe3+hydrolysis is proposed to interpret the reactions taking place in these three Solutions. In theR= 0 solution, the initial number of nuclei for condensation is low, whereas the poten‐tial supply of Fe(OH)3is abundant. In theR= 1 andR= 2 Solutions the number of nuclei initially formed is high, whereas a limited amount of mono‐meric Fe(OH)3is available for condensation. The initial number of nuclei relative to the concentration of monomeric species is the key factor that governs the appearance and properties of th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01637.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryGamma‐radiation, backscatter gauges, as normally employed for the determina‐tion of the bulk density of soils, use integral mode counting. They are relatively insensitive to the presence of soil moisture and hence not generally suitable for monitoring soil moisture content, particularly, if the soil type effect is minimized by counting only gamma‐photons of energy>0.400 MeV for a137Cs source. However, using differential mode counting with the window set at about 0.08 MeV, the phenomenon is one of multiple instead of single scattering. With a source‐detector Separation of the order of 20 cm, about eight Compton in‐teractions are obtained and, as a multiplying factor ofZjAis involved at each interaction, the increased response with hydrogen‐containing material is easily observable. The value ofZ/Afor hydrogen is 1.0, and for materials not containing hydrogen about 0.5; therefore for water it is 5/9. Hence under these conditions, the response for water compared with non‐hydrogen‐containing materials is [(s/9)/(1/2)]8= 2.32 times, an increase of 132 per cent. This method can therefore be exploited to measure the moisture content of soils. The sensitivity is high, and the accuracy is better than ± 5 per cent, which is not as good as can be achieved with a separate thermal neutron detector, but is useful for many purposes and, of course, only one instru

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01638.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryA method for extraction and determination of organic phosphorus based on a pretreatment with IM HC1 followed by ultrasonic Vibration in 0.5M NaOH is proposed and shown to be generally superior to two commonly used procedures in terms of efficiency and speed. Determination of organic phosphorus by the proposed technique showed that almost a third of the phosphorus applied to a red‐brown earth growing a mixed legume‐grass pasture has been incorporated into organic molecu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01639.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryTwo humic acids, extracted from widely different soils, have been fractionated with respect to molecular weight by means of gel chromatography. The resulting fractions were assayed for total nitrogen, amino acid nitrogen, phosphorus and sulphur.Nitrogen and phosphorus contents were greatest in the high molecular weight fractions and decreased considerably with decreasing humic acid molecular weight. The change in nitrogen content was accounted for mainly by the loss of amino acid nitrogen. By contrast, sulphur contents remained constant throughout the molecular weight range. These changes may reflect part of the process whereby nutrient elements, combined organically within humic acid, are made available for plant growth.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01640.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThe difficulty of illustrating soil pit detail can be overcome by using selected grey density slices of original photographs. The technique of density slicing for illustrations involves the separate printing of a particular shade of grey from the original, which picks out the detail required.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01641.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThree stages in the study of soil variation are recognized: the identification of major soil types and gradients, the establishment of the location of types on the ground and on a map, and the understanding of the causes of soil variation. Evaluation of the causes of variation may be hindered if the stages are not kept separate and a strategy is suggested to achieve this separation. Principal components analysis and numerical classification are used first to produce a rigorous description of soil variation which is presented in map form. This description is a basis for the generation of hypotheses about the causes of soil variation. This strategy is used to examine soil variation in some beech woods and farmland of the mid‐Cotswold Hills, Gloucester shire, and a hypothesis is suggested that variation in soil moisture is most important in this are

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01642.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryIsotopic exchange of phosphate ions between soil and solution was examined with particular emphasis on the slower reaction involving the incorporation of the tracer in the solid phase that follows the very fast exchange reaction between the solution and the surface of solid. Experimental data fitted both an equation composed of a sum of exponentials and a much simpler two‐constant equation. The goodness of fit was similar in each case but it was concluded that the exponential type of equation was not useful as a means of elucidating the mechanisms involved. The two‐constant equation may be derived from the kinetics of crystallization and recrystallization processes, and therefore provides an interpretation which is amenable to experimental verificat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01643.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThe way pH changes in soil are propagated by movement of acids and bases is described. In acid soils the H3O+‐H2O acid‐base pair is most important, while in alkaline soils the H2CO3‐HCO3−pair is always dominant, its effect depending directly on the pressure of CO2. In neutral and slightly acid soils, soluble organic matter and the H2PO4−‐HPO24−pair may also contribute.A soil acidity diffusion coefficient is derived, and defined as:wherevl= the volume fraction of the soil solution,fl= the impedance factor for the liquid diffusion pathway,bHS= the pH buffer capacity of the soil,bHB= the pH buffer capacity of each mobile acid‐base pair,DlHB= the diffusion coefficient of each mobile acid‐base pair in free solution,and the sum is taken over all mobile acid‐base pairs.The soil acidity diffusion coefficient may be used to predict the course of pH equilibration in practical situations. It is high in acid and alkaline soil, and at a minimum in slightly acid soil. It is little affected by variation of the ionic strength of the soil solution at concentrations less than 0.01M. When the pH buffer capacity of the soil is constant, and only the H3O+‐H2O and H2CO3‐HCO3−pairs are important, the soil acidity diffusion coefficient varies as cosh{2.303(pH—pH0)}, where pH0is the pH at which the soil‐acidity diffu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01644.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummarySamples from fifty‐eight arable topsoils in south‐eastern Scotland were analyzed for compactability, plasticity, organic matter content, particle density, and particle‐size distribution. The samples were classified by the methods employed for engineering soils and the groupings so obtained were compared with the textural classes. The criteria for the classification of engineering soils provide useful information on the likely mechanical behaviour of arable soils in the field. Tests were made for correlation between fifteen soil properties. The organic matter content, which in the samples studied ranged from 2 to 10 per cent, was shown to influence several mechanical properties, including optimum moisture content, maximum dry bulk density, liquid limit, and plastic limit.Maximum bulk density and optimum moisture content were strongly correlated with Atterberg limits and organic matter content. The liquid limit was more closely correlated with particle‐size distribution than was the plastic limit. Unlike soils encountered in engineering, the particle density of these soils was not correlated with particle‐size distribution but, like the Atterberg limits, was strongly correlated with organic matte

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1972.tb01645.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY