摘要:

SummaryMost methods for the determination of structure require the soil to be freed of water and yet to retain its original character. The methods of freeze‐drying and critical point‐drying are examined and it is concluded that they are not generally satisfactory. It is possible to preserve the soil fabric whilst water is slowly exchanged with an organic solvent (e.g. methanol or dioxan). The fabric is hardened and the degree of hardening is increased by subsequent exchange with certain water‐immiscible solvents (e.g. diethyl ether). Some shrinkage must be tolerated when it is desired to remove the liquid from the fabric. The best method was found to be infiltration by liquid carbon dioxide and its removal above its critical temperature. Despite some shrinkage the fabric seems unch

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00765.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe paper reviews some quantitative aspects of the hydrodynamic dispersion of solute that occurs under the combined influence of molecular diffusion and convection when a solution flows through a porous material. In particular, the paper (i) describes several methods of analysing the breakthrough curve of one solution as it displaces another from‐ a column of porous material to yield a coefficient of hydrodynamic dispersion (K); (ii) discusses the form of K as a function of particle size and fluid velocity in granular beds composed of solid particles or of aggregates; (iii) discusses the effect of K on the dispersion observed in a column of porous material, as fluid velocity and particle size vary, as an aid in assessing the efficiency of leachin

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00766.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryAnnually, for the past 12 years, a consecutive cereal‐cropping sequence was begun. During 1969–72 soil was collected from plots with similar fertilizer treatments, but with different sequences of crops. In 1971 and 1972 wheat seedling bioassays showed that take‐all disease became miximal after two or three crops, decreased to the fifth or sixth crop and then remained fairly constant in the‘take‐all decline’state.The sequence with maximum disease had most NH4+‐N and least NO3‐‐N in the rhizosphere soil in spring 1972, but there were no similar relationships in bulk soil in either of 2 years. Soil and rhizoplane populations of ammonifying and denitrifying bacteria were notably smaller in autumn 1970 and 1971 in short cereal sequences (2‐5 yr.) than in the longer sequences. After γ‐irradiating or autoclaving irradiated soils, all sequences contained much NH4+‐N and although disease developing from added inoculum differed among soils, it did not follow the take‐all decline pattern. Diffusate from sterilized soil favoured growth of the pathogen (Gaeumannomyces graminisvar.tritici) least when it originated from the sequence that

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00767.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryMethods are described for measuring the changes in the horizontal and vertical distribution of packing state and cone resistance following the passage of wheels and tracks over prepared beds of soil. A gamma‐ray transmission system was employed with automatically controlled scanning in a 2 × 2 cm grid in soil sections of 1.08 m length by 0.3 m depth, using a scintillator/photomultiplier detector assembly with stabilized pulse‐height analysis and magnetic tape recording. Changes in cone resistance were measured in a 2 cm (vertical) by JO cm (horizontal) grid in a section 1.4 m length by 0.5 m depth using an electrically driven penetrometer with load and displacement simultaneously recorded on an XY plotter and magnetic tape. Results were analysed and displayed graphically by computer with packing state expressed by a number of optional properties (dry bulk density, total porosity, air‐filled porosity, void ratio, or specific volume).Pronounced differences in packing state and soil strength were observed as a result of the passage of a two‐wheel‐drive tractor, with and without cage wheels, and a crawler tractor. Adding a cage wheel decreased slightly the compaction below the rubber tyre, but formed a partially compacted zone below the cage wheel. Increases of dry bulk density and soil strength were recorded below the crawler track but the values for these properties did not reach the maximum values found below the r

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00768.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe development of soil classification as a basis for soil mapping in England and Wales is briefly reviewed, and a system for future use is described. The things classified are soil profiles, and classes are defined by relatively permanent characteristics that can be observed or measured in the field, or inferred within limits from field examination by comparison with analysed samples. Profile classes are defined at four categorical levels by progressive division, and are termed major groups, groups, subgroups, and soil series respectively.Classes in the three higher categories are defined partly by the composition of the soil material and partly by the presence or absence of particular diagnostic horizons, or evidence of recent alluvial origin, within specified depths. Soil series are distinguished by other characteristics, chiefly lithologic, not differentiating in higher categories. Most of the soil groups, regarded as the principal category above the soil series, are closely paralleled in other European systems, in the U.S.D.A. system (7th Approximation with subsequent amendments), or in both. Compared with the system used hitherto, the main innovations are the use of specific soil properties to define classes at all categorical levels, and the separation at group level of classes based primarily on inherited lithologic characteristics.The soil‐profile classification provides a uniform basis for identifying soil map units, considered as classes of delineated soil bodies. When a map unit is identified by the name of a profile class, it is implied that most of the soil in each delineation conforms to that class, and that unconforming inclusions belong to one or more closely related classes or occupy an insignificant proportionate area. Map units identified by land attributes not differentiating in the profile classification are termed phase

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00769.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe amount of aluminium sorbed by calcium bentonite from basic aluminium chloride solutions depends on the ratio of OH to A1 in the original solution. Except when OH/A1 = 0, only part of the sorbed A1 is exchanged by dilute solutions of barium or calcium chlorides and the exchange capacity of the clay decreases in proportion to the amount of aluminium retained by the clay. Al‐bentonite appears to contain a mixture of A13+and a basic cation in which OH/Al is 2.5. Neutralizing Al‐bentonite with calcium acetate of pH 7.2 restores only part of the exchange capacity and some charged interlayer aluminium is thought to remain in the clay at this pH. It seems possible, therefore, that charged interlayer aluminium may be found even in soils with a neutral react

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00770.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryThe bulk density, available water (Aν), air capacity (Cα), and retained water capacity (θν) were determined for 158 A, B, and C horizons of field soils. Clay (<2 μm) and silt (2=60 μm) were also determined. Statistical analysis of the results demonstrated that bulk density exerts a profound influence onAν, Cα, and θν, but the effect varies between texture groups and horizons. Significant negative correlations were obtained between bulk density andCαfor most texture and horizon groups. In B and C horizonsAνand θνalso decrease with increasing density, whereas in A horizonsAνand θνtend to increase with bulk density except in silty soils. Within a limited range it is feasible to control these parameters by using field techniques to achieve optimum bulk density for

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00771.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryMo, V, and U are mobilized as anions by aerobically decomposing plant matter; the behaviour of the dissolved metals differs in several respects from what would be expected in inorganic systems.With respect to dialysis through cellophane, between pH I and 4 the mobilized Mo is fixed by colloidal organic decomposition products, with maximum retention at pH 1.5; V is retained between pH 1.5 and 7.0, with a maximum at pH 3. The specific fixation of Mo and V by soil organic matter was considerably less, and persisted over wider pH ranges–1.5‐6.5 and 1.0‐9.0 respectively. The fixation of U by both forms of humified organic matter increased sharply to a maximum around pH 4‐5, and thereafter decreased slightly up to pH 8.The anionic forms of the three elements persisted when MOO:2‐4, VO;‐3and UO, were incubated with anaerobically decomposing plant matter; under these conditions V(V) was probably reduced to V(IV), and it seems that an anionic V(IV) complex was formed.Although the molecular size of the colloidal decomposition products of lucerne was somewhat less than that of organic matter extracted from Rothamsted top soil, acid hydrolysates of the two humic acids contained the same twenty‐three amino acids, in much the same relativ

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00772.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryDetails of soil‐water profiles between drains and the associated drain‐flow data are presented for the winter period on a clay soil of the Ragdale series, formed in drift over Lias clay in the Midlands of England. A conventional water‐table is shown to exist and the rate of drain flow is shown to depend on whether the water‐table is high enough to be within layers having a better hydraulic conductivity than the normal subsoil. Mole drainage is shown to modify the drainage performance considerably by providing a quicker disposal of water, and significantly lower water‐table subject to much smaller fluctuations in level. Where drains have been laid in the natural subsoil, without this being disturbed by deep cultivations, the water‐table level is frequently close to cultivation level and there appears to be little water movement in the subsoil. It is concluded that for effective drainage, soils of this type require deep cultivations to modify the subsoil and allow water movement at gr

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00773.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryExperiments on south‐facing ridges showed significant increases in soil temperature at 5 cm depth on the south slope of the ridge when compared with the ridge top and horizontal surfaces. The average maximum temperature was 2 °C higher halfway down the south‐facing ridge slope than beneath a horizontal surface and on certain individual days differences of up to 7 °C were recorded in maximum temperatures between the two positions. The ridge top temperature was intermediate between those on the slope and horizontal. Minimum temperatures were similar at all positions. The increased maximum temperature on the ridge slope significantly increased the accumulated temperature hours above 10 °C. The moisture status on the slope of a compact ridge followed closely that of a horizontal surface, being slightly lower during droughts. The ridge top dried out rapidly during droughts. The increase in maximum temperature and accumulated temperature hours above 10 °C, together with the acceptable moisture level found in the side of a compact south‐facing ridge should offer advantages either for earlier germination or for a more rapid rate of emergence

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb00774.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY