摘要:

SummaryThe magnetic susceptibility of soil minerals is discussed, and in particular that of the ferrimagnetic minerals, maghemite, magnetite, and the titanomagnetites since one or more of these usually dominates soil magnetic properties. The magnetic susceptibility of soil depends on the shape, size, and concentration of these minerals as well as on the method of measurement. Measurements performed in a weak alternating magnetic field are the most reliable.The identification, formation, and occurrence of soil maghemite is considered in detail since it is usually of pedogenic origin and occurs in (magnetically) detectable amounts in most soils. Moderate concentrations (>1 per cent) of magnetite or titanomagnetite in soils may be accurately measured if some of the material is first magnetically separated and its susceptibility determined. An example is given of the use of susceptibility measurements. Pedogenic maghemite may be determined in soils developed from parent materials of low susceptibility. A very rough value of 8.8 × 10−4m3kg−1is suggested for the mass susceptibility of such maghemite (excluding magnetic concretions).Although susceptibility has been suggested as an indicator of soil forming processes, this is only possible within an area containing fairly uniform parent mate

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02232.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe stress produced by raindrop impact, calculated as the rate of change of momentum divided by area of contact, was found to be only partly satisfactory in studies of breakdown of paper tissue and soil crumbs. The calculated stresses for failure did not agree closely with values found by other methods, and varied systematically with raindrop size. The differences were related to the effect of duration of application of stress, and to the concentration of stress around the periphery of the drop.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02233.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe rates of extraction of Na, K, Mg, Ca, and Al with 1M NH4NO3from the mineral‐and organic‐rich layers of some Park Grass (Rothamsted) soils were measured at the pH of the soil. Below pH 3.7 exchangeable Al, derived from the kinetics curve, increases with decreasing soil pH and is less in the organic‐rich layer. The sum of the basic exchangeable cations, ∑(Na + K + Mg + Ca), increases with increasing soil pH and is more in the organic‐rich layer.The extraction of exchangeable Al obeys first order kinetics, the rate constant being similar for all the soils (mean value 36 ± 7 × 10−6|s−1), which implies that exchangeable Al is released from surfaces with similar properties for the adsorption of Al, and that the rate is not affected by soil pH and organic matter. The rate of extraction of non‐exchangeable Al is the same in the mineral‐and organic‐rich layers of each soil, and is maximal at about pH 3.7, decreasing sharply at more an

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02234.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryIn some alkaline soils of Punjab (India) the adsorption, desorption and solubility relationships of lead and cadmium were investigated and the results analysed by the Langmuir equation.Both the metals are retained in soils by adsorption on mineral interfaces and interaction with organic matter and calcium carbonate. At high concentrations, these probably precipitate as hydroxides. Sequential desorption of Pb and Cd with 1 MKCI and 0.05 MCu(CH3COO)2provided a measure of their exchangeable and chelated form.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02235.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummarySodium‐calcium exchange equilibria in soils with a range of cation exchange capacity (CEC) and surface charge density (SCD), showed calcium preference whether the results were interpreted by a thermodynamic treatment, by an electric diffuse double layer equation, or by an empirical approach. Surface soils preferred Ca more than the corresponding sub‐soils, which was mainly attributed to their higher SCDs and organic carbon contents (OC). Significant correlations between OC and (ΔGo)ca→Na, and OC and SCD, suggest the effect of OC on Ca preference to be mainly through increased SCD rather than to specific ion exchange sites.Significant correlations between ΔGoand SCD, ΔGoand KG(the Capon constant), and between corrected SCD and KG, suggest that all three approaches can be used to describe Na:Ca exchange equilibria in these soils, and that the equilibria are related to intrinsic soil pr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02236.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryAdsorption isotherms were obtained for fulvic and humic acids on synthetic gibbsite and goethite and on a natural imogolite. The results were interpreted with the help of spectra of the adsorption complexes, and measurements of hydroxyl displaced. The mechanism of adsorption involved ligand exchange with the surface hydroxyl groups and hydrogen bonding. The hydroxyl groups displaced included singly coordinated species on the (100) face of goethite and on the edge faces of gibbsite. The doubly coordinated hydroxyl groups on the (001) face of gibbsite were not replaced, and this face adsorbed only un‐ionized fulvic acid probably by a hydrogen bonding mechanism. Imogolite adsorbed most fulvic acid because of its high porosity. Only isolated places on its surface reacted with fulvic acid to form carboxylate group

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02237.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryInfrared spectroscopy has been used to investigate the complexes that are formed when acids are evaporated onto goethite. It is probable that, like HPO2−4, the anions SO2−4, SeO2−3, and oxalate are adsorbed by ligand exchange and form binuclear bridging complexes where two singly coordinated A‐type OH groups are replaced by two oxygen atoms of one ligand. There is evidence that HPO2−4and oxalate are likely to be present in this form in wet environments, and this is probably also true for SO2−4and SeO2−3.Fluoride ions can completely replace the singly coordinated A‐type OH groups but do not replace C‐ or B‐type OH groups that are coordinated, respectively, to two and three Fe3+ions. The other halides, nitrate, and benzoate partially replace the A‐type OH groups, benzoate being adsorbed as a monodentate ligand.Copper ions do not appear to react with A‐type OH but zinc ions are probably adsorbed on the goethite (100) face in conjunction with c

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02238.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryAn explanation is put forward for the shape of adsorption envelopes found for phosphate adsorption by various metallic oxides. The equationxm= C1(μH3PO4+μ∑anions) is proposed, where μH3pO4is the chemical potential of undissociated H3PO4; μ∑anions is the chemical potential of all phosphate anions considered as one. component;C1is a constant that includes influences of surface charge, chemical affinity of the metal for phosphate, specific surface area, etc., andxmis the calculated Langmuir maximum adsorption of P at each pH. The dependence of C1on the metal present in the oxide i

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02239.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryAdsorption‐desorption and isotopic‐exchange isotherms for acids soils of known clay mineralogy indicated that when all the surfaœ P accessible to the solution was considered, the bonding energy for phosphate decreased exponentially with site coverage. The soils differed markedly in the quantities of surface P held at sites of very high bonding energy, defined as those in equilibrium with a solution concentration1mM), and the use of soils that are naturally in dis‐equilibrium because of recent fertilizer additions or severe depletion of P by

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02240.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryAn estimate is given of nitrogen losses which could occur through chemical decomposition of nitrite formed by nitrification of ammonium in acid tropical soils. Experiments on the rate of disappearance of nitrite were carried out in acid buffers as well as in soil samples. Numerical solutions of a system of differential equations describe the nitrification process and the chemical denitrification reaction. Up to 50 per cent of added ammonium nitrogen may be lost in an acid soil when nitrification occurs at temperatures prevailing in the humid tropics.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02241.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY