摘要:

SummaryThe agricultural background, morphology, and classification of soils from the Hans lope, Ragdale, Evesham, Denchworth, Flint and Salop series are presented together with basic analytical measurements of particle size and chemistry and with some details of the field water regimes. This information serves as essential background to other studies of soil structural properties as they relate to management of the same soils.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00996.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryMacroporosity (>60 μm) in the three pairs of soils described in Part I was measured and characterized by image analyses. There are significant differences in macroporosity between the soils in each pair, particularly in the subsoil horizons. The results show that the Ragdale, Denchworth and Salop soils are more impervious than those of the Hanslope, Evesham and Flint soils.Comparison of the image analysis results with those derived from air content at 0.05 bar suction shows that in most cases macroporosity by the former is larger. In image analysis the maximum diameter of each pore is measured whereas the water retention method measures the diameter of the smallest exit point of each pore. Differences between the two types of measurement will thus be at a maximum in soils containing many large pores with narrow exit necks

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00997.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe response of three pairs of soils having contrasting management behaviour to changes in water content was investigated by measuring moisture characteristics, shrinkage, and pore size distributions by mercury porosimetry. Sample preparation for mercury porosimetry was by direct drying, or water replacement by methanol and liquid CO2followed by evaporation above the critical temperature. In heavy textured horizons, water release on shrinkage between ‐0.05 and ‐15 bar matric potentials occurs when pores of 10–200 nm equivalent plate separation contract. Structure development is dependent on the stability and regeneration of pores in the size range 200 nm‐30 μm during cycles of wetting and drying. Soils with little stable porosity in this size range show nearly normal shrinkage and have coarse structural units, whereas soils with stable or regenerating porosity depart more from normal shrinkage and structure in the profile tends towards a finer per unit. The application of mercury porosimetry shows promise for determining possible porosity limitations in soil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00998.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryPorosity and gas diffusion have been measured within dry crumbs sieved from the horizons of one soil from each of the Hanslope, Ragdale, Evesham, Denchworth, Flint and Salop series. Crumb porosities, ɛc, ranged from 0.19 to 0.33, dimensionless gas diffusivities, Dc/D0, from 0.015 to 0.098, and the effectiveness of unit pore space for diffusion, given by αc= (Dc/D0)/ɛc, from 0.06 to 0.29. Values of ɛcand Dc/D0were used to calculate complexity factors kcfor the crumb pores. The results are discussed in terms of soil texture, pore size, ease of soil management, and the frequency and intensity of wetting and drying of the soil in each horizon. None of the results suggests why the soils of the Ragdale, Denchworth and Salop series should be more difficult to manage than the oth

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb00999.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThree pairs of soils were chosen, each with one difficult and one easily manageable soil with similar texture. Mechanical composition and organic matter content greatly affected the measured physical properties some of which related to the field behaviour of each pair. Soils from all horizons were stable to water slaking except some subsoils on the Ragdale, Hanslope, Salop, and Flint series. Dry and total mechanical slaking were less and breaking strengths more for the Denchworth, Evesham, Ragdale and Hanslope series than for the Salop and Flint soils. Water‐holding capacity was largest for the Denchworth and Evesham soils, but slow penetration of water into their dense clods could influence regeneration of tilt

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01000.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryAn ultrasonic method has been used to measure the stability index, σ, for each horizon of six soils. They provided three soil series comparisons: Hanslope‐Ragdale, Evesham‐Denchworth and Flint‐Salop, in which the first‐named series in each pair is ‘rarely problematic’, and the second ‘commonly problematic’ in management.The results for the top soils are presented in terms of the relationship between σ and the concentrations of those soil constituents likely to contribute to stability of aggregates: organic matter, clay, iron and aluminium oxides, and calcium carbonate. Regression analysis indicates significant correlations for all except the iron and aluminium oxide components.For each soil pair, the ultrasonic measures of stability did not reflect soil management experience, either for surface or sub‐soil horizons. In general the commonly problematic soil appeared to have the same if not higher stability than its rarely problematic partner. Ultrasonic measurement of stability to dispersion, whilst indicating possible mechanisms of soil aggregate formation and breakdown, gives little help in identifying soil m

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01001.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryNatural aggregates of topsoil samples of six British soils (Hanslope, Ragdale, Evesham, Denchworth, Flint and Salop) were incubated with added nutrients and changes in their stability to wet sieving determined. Under anaerobic incubation the type of nutrient added had little effect on stability. Aerobic incubation with glucose gave a larger proportion of stable aggregates than with water. With peptone stability usually decreased, and occasionally increased, which may indicate differences in the binding mechanisms of the soil particles. Both sterile and unsterile aggregates incubated with water became more stable than controls; the rapidity of this change suggested a physical, rather than microbiological cause. Very stable grassland aggregates changed little on aerobic incubation with water, but became more stable with solutions of glucose or peptone. Artificial aggregates made from the same soil developed considerable stability to water on aerobic incubation, but remained almost totally unstable when incubated anaerobically.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01002.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryThe soil deformation and shear strength characteristics of three clay soils were determined at different moisture contents and spherical pressures, using a quick un‐drained triaxial compression test. The soils were found to deform either in a compressive way or by brittle fissuring, depending upon the relative values of moisture content, dry density and spherical pressure. The critical state concept of soil deformation can explain qualitatively the behaviour of these spils at high moisture contents but not at low. The Bridgman concept for fracture in brittle materials describes the soil behaviour at low moisture contents.The shear strength of the clay soils tested was more closely related to the soil moisture suction and to the amount of shrinkage which occurred on drying than to the absolute dry bulk density. The influence of moisture content and spherical pressure on the effectiveness of certain cultivation operations are considere

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01003.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryUsing aggregates from 2 clay soils over a range of water contents from pF 1 to oven dry, shrinkage and water release curves were measured and pore size distributions found by mercury porosimetry after critical point and after freeze drying.Freeze drying caused less shrinkage, the maximum being 6 cm3100 g−1from pF 1, but gave a large increase, up to 10 cm3100 g−1, of pores in the 0.1–10 μm size range.Critical point drying produced more shrinkage from pF 1, more than half of which was attributed to loss of interlamellar water and the rest to the collapse of pores larger than 10 μm.In these clays the volume of pores of over 3 μm diameter was very small (<3 cm3100 g−1) and most of the plant available water was released by collapse of narrower pores and not by por

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01004.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY

摘要:

SummaryTwo dual‐probe gamma‐ray transmission systems using caesium‐137 sources were examined. The performance of a small Geiger‐Muller detector was compared in respect to spatial resolution and calibration characteristics with an NaI(TI) crystal detector fitted to a thermally stabilised narrow photo multiplier with variable photon energy discrimination. The NaI(TI) detector had progressively better depth resolution with increasing discrimination threshold and more linear calibration relationships than the GM detector. The calibration linearity and sensitivity with the GM detector were strongly dependent on the mass thickness of the probe wall tubing. Count rate was not dependent on soil composition with either system. The GM detector system provided a satisfactory instrument of restricted performance. For good spatial resolution near the surface a narrow photo multiplier with thermal stabilisation overcame some of the difficulties previously found with NaI(Tl) de

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1979.tb01005.x

出版商:Blackwell Publishing Ltd    

年代:1979

数据来源: WILEY