摘要:

SummaryPore size distributions obtained from the relationship between moisture content and suction are not dependable in fine‐textured soils because of shrinkage. To overcome this problem, methods such as nitrogen sorption, mercury intrusion porosimetry, non‐polar liquid desorption and thin sectioning have been used. In order to pre‐dry samples without changes in the pore system, freeze‐drying, organic liquid replacement of soil water, and critical point drying techniques have been employed. These methods of soil drying and pore size measurement are described and compared, and the validity of their use in soil studies is examined. The measurement of pore sizes by water desorption is also di

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02261.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe frictional behaviour of soil‐steel interfaces has been investigated under controlled conditions in the laboratory. The description of the behaviour by a Coulomb‐type expression has been verified in the normal stress range 10–280 kPa. However the effect of normal stress on density and hence on adhesion must be considered. Soil moisture content can change interface friction by up to 50%, the effect increasing as sliding speed is reduced. These effects have been explained by considering inter‐particle c

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02262.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryA layer model for the movement of solutes in soil has been developed in which, as a working approximation, the soil solution is partitioned into mobile and retained phases. Only the mobile solution is displaced during water movement, and equilibrium is assumed to be established between the mobile and retained phases when flow ceases, giving holdback of solute. The model permits the displacement of the mobile solution through an indefinite number of layers when large amounts of rain fall. It can be assumed either that water and solute are stored in the bottom layer and can be withdrawn up the profile by evaporation or that they drain from the bottom layer. Predicted soil nitrate concentrations agreed reasonably well with those measured in a field experiment and indicated some sensitivity to layer thickness. The capacity of the model to predict concentrations in drainage is demonstrated.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02263.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryFourteen surface and 6 subsurface horizons of Illinois soils adsorbed significant amounts of F−with release of OH−. At low concentrations, adsorption was described by both Langmuir and Freundlich isotherms. The calculated Langmuir adsorption capacities were related to pH, clay, organic carbon, and amorphous aluminum contents.Two soils with different gross chemical properties behaved in essentially the same manner, with adsorption maxima occuring between pH 5.5 and 6.5. The similarity between adsorption at different pH values for the soils and those for bauxite, allophane and synthesized ‘soil chlorite’, and the lack of adsorption maxima between pH 5.5 and 6.5 for pure kaolinite and montmorillonite, suggest that F−adsorption in the soils is due primarily to the presence of amorphous aluminum oxyhydroxides which are common weathering products in th

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02264.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryParameters of the exchange equilibria for three pairs of cations of agricultural interest (K/NH4 – Ca/Mg – K/Ca) were experimentally determined. The selectivity coefficient of the two homovalent pairs was found to be constant, whereas that of the mono‐divalent pair depended on the total concentration of cations in the solution and on the exchange capacity. Equations are given which describe the exchange equilibria in peat, which take into account its pH‐dependent exchange c

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02265.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe sorption of inorganic phosphate (P) by soils and hydrous ferric oxides was studied at times up to 192h. An initially rapid decrease in solution P concentration was followed by a much slower decrease between 48 and 192h with soils, Fe gel. and natural goethite, whereas synthetic goethite gave a well‐defined equilibrium condition after only 48h. Resolution of the sorption isotherms showed that the increase in P sorption with time involved an appreciable shift of P from a more‐physically sorbed form to a chemisorbed form. This was supported by chemical fractionation which showed that NaOH‐extractable P was fairly constant with increasing sorption time, whereas the additional sorbed P was extracted by citrate‐dithionite‐bicarbonate from soils, and by HC1 from Fe gel and natural goethite. These sorbents contained short‐range (amorphous) material, whereas synthetic goethite, from which all sorbed P was NaOH –extractable. did not. It is proposed that the time‐dependent sorption of P and the associated shift of P to chemisorbed forms, involves the diffusion of P into “structurally porous”, short

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02266.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummarySorption of added inorganic phosphate (P) was irreversible in four contrasting soils and hydrous ferric oxide gel during 16 h desorption after 40 h sorption at the same (iso)pH. Irreversibility increased with increasing time of desorption above 30 h. When the amount of P which was chemisorbed during the sorption step was subtracted from the amount desorbed, the latter fell on the isotherm describing the more‐physical, potential‐determining sorption. No pH change occurred during desorption and net negative charge decreased by 1 equivalent per mole P desorbed.These results suggested that only more‐physically sorbed P was desorbed at the iso‐pH. The more‐physically sorbed P was also reversible with respect to changes in the ionic strength and cation species of the desorbing solution. The isotopic exchangeability of the more‐physically sorbed P was at least ten times greater than that of chemisorbed P. With increasing sorption time, both the ease of desorption and exchangeability of sorbed P decreased. Subsequent to desorption, the exchangeability of the remaining sorbed P also decreased. These observations are interpreted in terms of the concurrent changes in the amounts of chemisorbed and more‐physic

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02267.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryThe kinetics of isotopic exchange of phosphate on hydroxyapatite, amorphous aluminium phosphate, phosphate‐treated aluminium oxide and dicalcium phosphate dihydrate were studied in aqueous suspensions as a function of solid/solution ratio and amount of added isotope. The tracer exchange reaction was independent of time for the dicalcium phosphate due to a very small amount of exchangeable phosphate found in the solid and to the high solubility of the material. For the other phosphates, a power function and/or a function composed of a series of exponential terms were found suitable for representing the tracer kinetics. The theoretical background for both functions is shown to be approximately the same. Both describe tracer kinetics for a system containing more than one solid phase. The amounts of exchangeable P were found to depend strongly on the solid/solution ratio but not on the amount of radioactivity added. The dependence of the tracer kinetics on the solid/solution ratio is due to the ageing processes that give rise to the formation of surface layers having physical and chemical properties different from those of the bulk soli

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02268.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryInfrared spectroscopy and chemical degradation indicated several fulvic acid fractions from an iron‐humus podzol capable of complexing and translocating metals. Acidic polysaccharides, some of them resembling pectic acid, were isolated in appreciable quantities. These are able to bind metals through carboxyl groups, but peptide components present in the polysaccharide fraction may provide alternative metal complexing centres. The high yield of acid‐extractable organic matter from the illuvial humus, together with its high content of carboxylic acid groups, make it likely that this fraction plays a major role in the translocation of metals. Phenolic compounds allegedly associated with this process were present in the fulvic acid solution in low amounts, and only in the extracts from the organic horiz

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02269.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY

摘要:

SummaryHumic acids from the L layer and B2hhorizons of a humus‐iron podzol were fractionated by gel permeation chromatography. Elution of the gel column with distilled water adjusted to pH 7.5 gave a fractionation based on both gel permeation and adsorption chromatography. This procedure gave filtered products containing most of the organic nitrogen, and an absorbed fraction. The latter contained most of the components which gave benzene carboxylic acids on oxidation of the humic acid with dilute nitric aci

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1977.tb02270.x

出版商:Blackwell Publishing Ltd    

年代:1977

数据来源: WILEY