摘要:

SUMMARYBreakthrough curves have been determined using an analytic solution of the dispersion equation for constant water content—set equal to the mean water content—and compared with those obtained for the actual water distribution using an analysis developed by Wilson&Gelhar (1981). Numerical analysis of selected examples confirmed the validity and accuracy of the latter method.The error in using the mean water content could become unacceptably large when the water content range was large or changed abruptly with distance, but was other‐wise small and probably negligible for many applications. It was not possible to devise simple criteria, but the method of Wilson&Gelhar is simple to apply, and it is unnecessary to consider alternative approximate me

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00291.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYESR—SAR relationships of 623 soil samples from arid and semi‐arid zones in Israel were found to depend on soil salinity and cation exchange capacity as reflected crudely by the saturation percentage. The Gapon constant decreased as salinity increased and, for a given salinity level, it also decreased as the soil saturation percentage (SP) increased. There was no relationship between ESR and SAR for soils with low SP values (20–40) or low salinity levels (0.2–2 dSm−1). Regression equations are presented for different salinity and saturation percenta

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00292.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYSurface charge of mixtures of lepidocrocite and illite determined by adsorption of potential‐determining and electrolyte ions is studied as a function of pH and NaCl concentration. Deviations between results obtained by both methods were a function of the illite content of the mixtures, and can be mainly attributed to coatings of hydroxyaluminium complexes on the constant charge surfaces of the clay mineral, which can react with H+ions or release exchange sites by precipitation of well‐formed hydroxides. These coatings of aluminium complexes can cause H+consumptions similar to those due to lepidocrocite.Some ideas are put forward for modelling charge properties of mixed syst

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00293.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYInfrared spectroscopy was used to show that arsenate is adsorbed on the surface of synthetic goethite (α‐FeOOH) as the acidic HAsO42‐ ion, replacing singly coordinated surface OH groups. In this respect, arsenate is analogous to phosphate, but its larger size apparently causes it to interact more strongly with some of the OH groups that remain on the surface. This has suggested an alternative assignment for the absorption bands of these OH gr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00294.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe retention of NH4+ and Ca2+ on soil and weathered pumice samples containing constant and/or variable charge components was measured in different NH4CI‐CaCl2solutions. The NH4+/Ca2+ selectivity of each sample was evaluated using a quotient of the partition of NH4+ on the exchange sites and in the solution relative to that of Ca2+. It increased with decreasing pH and increasing NH4Cl‐CaCl2concentration for a given equivalent fraction of NH4+ in the solution. These effects were quantitatively explained in terms of the changes of NH4+ and Ca2+ concentrations in the solution and in the diffuse double‐layer of the ion‐exchange material as predicted by the law of mass action and the electric double layer theory. The NH4+/Ca2+ selectivity of different exchange materials showed a similar variation among their exchange sites and increased in the order humus, allophane and imogolite (Si/Al ratio 0.5)

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00295.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe standard and differential thermodynamic properties of K‐Ca exchange in soils from the Broadbalk (Batcombe series) and Saxmundham Rotation I (Beccles series) Experiments were evaluated for selected manurial treatments, using exchange isotherms and calorimetric measurements. The Beccles soil had a greater preference for K than the Batcombe soil in all the comparable treatments (Nil, PK and FYM). In all the soils, enthalpic forces favoured K preference but entropic forces Ca preference; in all but two cases the magnitude of the enthalpic forces were greater, resulting in K preference (positive ‐ΔGo). The ‐ΔHovalues of the soils did not vary greatly, and the main cause of variation in ‐ΔGovalues was that in ‐TΔSovalues. Residual fertilizer K and FYM residues decreased preference for K at both locations, but more so at Broadbalk than at Saxmundham, presumably because of the greater duration and amount of K manuring at Broadbalk. FYM residues had a very complex effect on the exchange characteristics of Broadbalk soil. It is suggested that these differences are caused by the different pH values of the surface soils before they came into arable usage, which reflect their contrasting parent materials and pedogenic histories, and by the different durations and extents of manuring in the tw

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00296.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYSurface soils from six ADAS long‐term experiments, including two on Andover series, were examined for K‐Ca exchange by exchange isotherm and calorimetric methods. Preference for K decreased in the order Worcester>Clwyd>Newport. The latter two acid soils showed ‘no preference’ and Ca preference respectively. Preference for K decreased with decreasing surface area and increasing surface charge density. The enthalpic factor favoured K preference in every soil, but the entropic factor favoured Ca preference in all but one soil. The magnitude of the enthalpic factor was greater than that of the entropic factor, resulting in K preference, in the Andover, Hanslope and Worcester soils, while the reverse was the case in the Newport soil. In the Clwyd soil, enthalpic and entropic forces were counterbalanced. These relative contributions were related to the interactions between clay mineralogy, pH and manurial history.Differential heat measurements, ‐d (ΔHx)/dxrevealed exchange site heterogeneity in five of the soils. Five regions of constant ‐d (ΔHx)/dxwere found, ranging from 6 to 12 kJ eq−1, a maximum of three occurring in any one soil. These were assigned to montmorillonite (two regions), mica, hydrous mica and vermiculitic mica surfaces. The 2: 1 phyllosilicate contents of the clay fractions of the whole soils calculated thus differed from those determined by XRD analysis of the clay fractions.Residual K decreased the cation exchange capacity of some of the soils but did not alter their surface areas. Its effect on K preference, K binding strength and the arrangement of the components of the system (the entropic fact

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00297.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe forms of occurrence of Mn were examined in some acidic surface and sub‐soils from areas of permanent grassland using chemical extractants. Despite high total contents of Mn in some of the soils and low pH, only minor proportions occurred as exchangeable Mn2+. Much larger proportions were present as reducible hydrous oxides, e.g. up to 38% and 54% of the total contents in surface and subsoils, respectively, were present as hydroquinone extractable, or easily reducible, Mn. Reducible forms of Mn were poorly correlated with other more mobile forms. Large proportions of the total Mn contents were accounted for when estimates of different fractions were calculated from differences in amounts extracted by different individual extractants, i.e. M NH4OAc, 0.2% hydroquinone, 0.1 M pyrophosphate, and ammonium oxalate. The distribution of Mn amongst the different fractions as determined by a sequential fractionation scheme differed markedly from the distribution calculated by differences. In particular, there was a marked change in form after extraction with pyrophosphat

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00298.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe association of cobalt with manganese oxides was examined in some surface and sub‐soils from areas of permanent grassland in England. Hydroquinone (0.2% in ammonium acetate at pH 7.0) was used to extract easily reducible Mn oxides from the soils. Two sequential extractions with this reagent removed significant proportions of the total Co along with the Mn; no significant amounts of iron were extracted. Mn‐rich iron concretions were isolated from two of the soils and these contained from 230 to 880 μg g−1Co. Approximately 30% of the Co in the concretions was dissolved by two sequential extractions with hydroquinone with concurrent release of considerable amounts of Mn, but, as with the soils, not of Fe. The concretions contained 20–41 mg g−1Mn and 62–171 mg g−1Fe that were soluble in acidified H2O2. It was concluded that significant proportions of the Co in soils is associated with Mn oxides, and will show the same sensitivity to changes in acidity and redox p

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00299.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

SUMMARYThe additional nutrient absorbed by a surface releasing a solubilizing agent is predicted. The ‘solubilizing effect’ is defined. The nutrient solubilized may diffuse away from the surface as well as towards it. If the change in solution concentration of nutrient and solubilizing agent at the surface are abrupt, the fraction of nutrient solubilized that is absorbed at a planar surface equals 1/(1 +√DY/DX), where DY, DXare the diffusion coefficients of the solubilizing agent and the nutrient. At a spherical surface this fraction has to be multiplied by 1/(1 +√πDY/t2a), and at a cylindrical surface, appropriate for a root, by approximately 1/(1 +√πDY/t4a), whereais

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1984.tb00300.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY