摘要:

SummaryThe succession of Quaternary deposits in Britain records only small, fragmentary parts of a very complex history of Quaternary events resulting from many climatic fluctuations. Deep sea sediments provide a more continuous record, but correlation between the oceanic and terrestrial successions is at present extremely difficult, mainly because of the lack of absolute dates for older parts of the latter. The often conflicting evidence provided by indirect methods of dating and long‐distance correlation is illustrated by reference to the chalky tills of East Anglia and the English Midlands, and the importance of soil studies in elucidating regional Quaternary stratigraphy is emphasised.The scanty history of pedogenesis in various parts of Britain is tentatively related to the provisional succession of Quaternary stages. Important changes in soil development processes occurred in mid‐Flandrian times as well as in earlier cold and temperate (inter‐glacial) stages, Many features of unburied soils are probably early Flandrian or older relicts, and difficulties consequently arise over use of the word ‘palaeosol’. Interglacial relict features in soils on pre‐Devensian deposits (paleoaigillic subgroups) are distinguished from Devensian and Flandrian soil characters, but it is difficult at present to differentiate pedogenesis of successive interglacials.More than two‐thirds of England is covered by Quaternary deposits, mainly of cold periods, and these generally provide better agricultural soils than pre‐Quaternary sediments. Some relict features of both cold and temperate Quaternary stages also seem to be significant in determining the agricultural capability of British soils, but their effects need evaluating

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01013.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryFourteen samples of soils were collected from localities in England where crusting and consequent depression of seedling emergence had been recorded. Natural aggregates of these soils were sprayed with poly(vinyl alcohol) (PVA), subjected to simulated heavy rain, and dried under IR lamps. In most soils, aggregate stability was enhanced by increasing applications of PVA and crust formation was prevented. Some soils, however, were unresponsive to PVA and crusts formed whether or not it was applied.Responsive and unresponsive soils did not differ in particle size distribution, or porosity characteristics. Removal of iron oxides and organic matter did not alter their adsorption characteristics towards PVA. Unresponsive soils, however, were found to have the mineral chlorite as a major component and it is suggested that PVA is unable to bind particles together when the surfaces presented for adsorption of PVA consist of gibbsite, the interlayer material of chlorite.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01014.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryA statistical theory is developed for the brittle fracture of soil aggregates. Fracture is assumed to depend on the flaws, such as cracks and holes, within the aggregates, the weakest flaw limiting strength. An equation known as the third asymptote distribution of smallest values gives the distribution of these weakest flaws.The crushing strength of aggregates of five soils from South Australia and Queens land is compared with theory and agreement is good. Larger aggregates have smaller mean values of tensile strength than smaller aggregates at both ‐100 kPa and ‐153 MPa water potential. A sudden increase in strength occurs for aggregates larger than about 6 mm in the Queens land soils which is more marked with the drier samples. This is consistent with the idea that these larger aggregates are produced by the compacting effects of machinery, whereas the smaller aggregates are produced by the self‐mulching effect.Changes in the internal structure of beds of aggregates are described as a function of amount of uniaxial compaction. A statistical method gives information about the size distributions and relative positions of aggregates and voids within the compacted beds. Compaction occurred almost exclusively at the expense of inter‐aggregate porosity, and the largest voids were excluded first by com

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01015.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryNumbers of earthworms collected from direct‐drilled or ploughed land were studied during successive years on contrasting soil types sown with cereals.Samples were taken in autumn using a combination of chemical expulsion and hand sorting of soil. The population was consistently larger on direct‐drilled than on ploughed land, and the difference became greater in each successive year. Deep burrowing species were affected similarly to the population as a whole. Population differences on the two treatments were greater with spring — than autumn ‐ sown crops. After tine cultivation numbers were usually similar to those after ploughing.On a direct‐drilled clay soil on which straw had been either burned, or chopped and spread, no differences were recorded in the overall population. However, significantly larger numbers of deep burrowing species were found on the chopped and spread areas, whereas on the burned areas numbers ofAllolobophora chloroticawere significantl

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01016.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe use of a portable field probe for sampling soil gas gives the degree of replication necessary to allow for the local variability of soil gas composition over short distances, and mass spectrometry provides a quick and efficient method of analysis for gases at concentrations above 0.1% by volume. These methods can conveniently be combined and their use is illustrated by the determination of N2, O2, Ar, CO2and CH4in two soils having impeded gaseous exchange with the atmosphere.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01017.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryA cation exchange equation based on diffuse double layer (DDL) theory was tested on 26 surface and sub‐surface soils from 6 field experiments in temperate and semi‐arid tropical regions. Sodification (the fraction of total charge on the surface neutralised by the excess of Na+plus the deficit of Cl−), or the exchangeable Na percentage, ESP, of these soils in relation to SAR, the molar ratio (Na]/[Ca + Mg]1/2, was evaluated from the observed data on Na:Ca exchange in two ways, using the DDL equation: (1) by multiplying the surface charge density of the soil with a mean correction factor f (based on the whole isotherm) assuming no interaction between adjacent clay platelets; this predicted the sodification of the soils satisfactorily between 0–30 ESP, though at the highest SAR values (i.e.>60), predicted ESP values were significantly smaller than the experimental values for 23 of the 26 soils; (2) by assigning values to the extent of interactionYd(directly related to the electric potential Ψdmidway between adjacent clay platelets) over the whole isotherm;Ydwas found to increase by varying degrees in different soils with SAR and ESP. Also in 12 of the 15 pairs of soils compared, the mean value,d, over the whole Ca‐Na exchange isotherm was appreciably larger for surface soils (which had higher surface charge densities) than for the subsoils from the same sites.The suggestion that theYdparameter provides a better criterion than the f parameter for characterising and comparing Na:Ca exchange equilibria in contrasting soils is discussed in relation to the effects of soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01018.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe reversibility of the adsorption of phosphate on goethite was measured by diluting suspensions of goethite on which phosphate was adsorbed with large volumes of phosphate‐free solution at the same ionic strength. The effect on the reversibility of various adsorption and desorption conditions was studied, particularly pH, temperature, ionic strength and time of reaction.The apparent irreversibility of the adsorption reaction seems to be due to a slow adsorption reaction of part of the phosphate after a very rapid initial adsorption, with a similar behaviour when the phosphate is desorbed. When the total adsorption plus desorption time is long enough, both adsorption and desorption points tend to lie on a single curve which corresponds to the isotherm calculated according to the Stern double‐layer the

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01019.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummarySelenite was adsorbed on a positively charged hydrous alumina at a solution pH of 5.0, and the OH−released and changes in the surface charge were measured. The adsorption isotherm levelled off at high concentrations suggesting a definite adsorption maximum. The OH−released yielded a curvilinear relationship of increasing slope with the selenite adsorbed. The positive charge on the alumina surface was neutralized by the adsorbed selenite and the net charge became close to zero as the adsorption of selenite was near maximum.The molar ratio of the ligands (OH−+ OH2) displaced over selenite adsorbed was more than one at surface saturations of<0.5, but it was approaching one with increasing adsorption of selenite. The results are explained in terms of preferential adsorption of divalent (SeO23−) and monovalent (HSeO−3selenite on a highly positively and less positively charged surface respectively, in agreement with the VSC−VSP model of Bowdenet al. (1973; 1977). The supply of SeO23−for adsorption is considered to be favoured by an expected lower H activity in solution adjacent to the positively charged surface than that in the bulk solution.A general discussion is given on the ligand exchange adsorption of selenite, phosphate and sulphate on hy

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01020.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryExchangeable Mg appears to have no specific effect on soil hydraulic conductivity of A and C horizons of a sodic sandy loam soil (montmorillonite and kaolinite clay minerals) leached with solutions which cause clay swelling to be the dominant mechanism reducing conductivity (SAR<20, electrolyte concentration 10 meq per litre). There is some evidence of a specific effect when these soils are subsequently leached with water which causes clay dispersion to become important. Fresh loess in the A horizon dissolves in percolating rainwater, causing difficulties in the replication of experiments. It seems to give a small degree of ‘self protection’ to soil structure, a property likely to be operating in other soils affected by recent loess depos

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01021.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryEDTA extracts (pH 7.5–10.5) from a Danish sandy loam showed no significant (95% level) increase in amounts of aluminium, calcium, iron, and magnesium between three and nine months' shaking. The amounts were independent of the soil: solution ratio (1:10–1:50), the EDTA concentration (0.01 M–0.2 M), and crushing the soil (<0.25 mm or

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01022.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY