摘要:

SummaryAt low levels of annual rainfall, leaching of bases with falling percentage saturation follows a simple physical pattern, but as rainfall rises above a level sufficient for reasonable plant growth, intrusion of the biological factor leads to a recirculation of bases and even to an accumulation in the solum with the result that percentage saturation rises once more to an optimum at about 46 in. rainfall and falls away with further increase in rainfall.These changes in percentage saturation are independent of the base‐exchange capacity of the parent material, and the total exchangeable bases in a soil are determined by the base‐exchange capacity of the parent material and the rainfall régime to which it has been subje

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00674.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

summaryWind action has modified relics of river systems which drained the southern and central parts of Western Australia. Dunes of both coarse crystalline and fine floury gypsum and lunettes of sand, silt, or clay size material are common near to the leeward margin of salt lakes. Further removed, materials, blown out from the lake areas as aggregates of clay, silt, and sand, are deposited as sheets which are medium‐textured and have a high lime content. The latter deposits have been termed lake parna

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00675.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryTechniques are described for the preparation and mounting of soil monoliths with a depth of 1‐1·5 in. The material is fixed with cellulose acetate and mounted in a way suitable for permanent exhibition. The preparation and preservation of hand specimens of special fragments are also describ

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00676.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryNatural and artificial systems of classification are defined. One of the most advanced natural systems of classification is the Periodic Classification of the Elements and its development is traced so that it can be used as a framework of reference for other systems of classification, in particular those for plants and soils. It is demonstrated that plant classification is also a mature system, but soil classification is still in an elementary stage of development. The strengths and weaknesses of two recently published systems, the Soils of Europe by Kubiena and the 7th Approximation by the Staff of the U.S. Soil Survey, are discussed.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00677.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryThe increase in thickness of dry orientated flakes of Ca‐montmorillonite about 0·2 mm. thick, prepared from Wyoming bentonite, when brought into vapour equilibrium with solutions of increasing relative vapour pressure has been measured with a travelling microscope. The three solutions used were sat. NH4H2PO4(P/P0= 0·92), sat. Ba(NO3)2(p/p0= 0·985), and water (p/p0= 1·0). X‐ray and water‐absorption measurements were also made on separate portions of the flakes at these values ofp/p0.The density of the dry clay and the apparent density of the dry flake were determined. As the lateral swelling of the flakes was found to be very small compared with the swelling perpendicular to the general plane of orientation of the crystals, the distribution of air and water in the flakes could then be calculated at each value ofp/p0.Up top/p0= 0·985, 80 per cent. of the water absorbed by the flake was accounted for by the increase in the thickness of the water films on the clay crystals, the remaining water filling about half the pore space. On the basis of the total volume of the flakes, the total pore space was reduced by 12 per cent. atp/p0= 0·92 compared with the dry flake, due to expansion of the crystals, but then remained the same up top/p0= 0·985. Betweenp/p0= 0·985 and 1·0, the pore space in the flake was filled and a further small expansion of the flake occurred, but the (001) spacing did not increase beyond 18·9 Å. Swelling in the vapour phase was unaffected by addition of I per cent. CTAB to the clay. The relation between macroscopic swelling and increase in water‐film thickness is consistent with the crystals being in the form of a tactoid.The swelling asp/p0→ 1·0 was much lower than that of a flake immersed in liquid water (see Part 2). It is suggested that this arises from the formation of polymolecular layers of water on the surfaces of the clay crystals, due to the influence of the exchangeable‐Ca ions which differ in structure

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00678.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryStarting with orientated flakes of dry Ca‐montmorillonite (Wyoming bentonite) about 0·2 mm. thick, the swelling of the flakes when immersed in 2 M CaCl2was measured with a travelling microscope. The further expansion when the flakes were brought into equilibrium with successively more dilute CaCl2solutions was also measured. The swelling of the flakes in 2 M CaCl2was equal to that of flakes equilibrated with saturated water vapour. As the CaCl2concentration was reduced the flakes swelled progressively, with negligible increase in the (001) spacing. This swelling was independent of the pH of the CaCl2solutions and could not be reversed by increasing the concentration of CaCl2. Flakes prepared from clay suspensions to which 1 per cent. of CTAB had been added did not swell in dilute CaCl2solutions.Measurements were made of the swelling of flakes under an applied suction. Suction reduced the swelling as compared with free solution, and the swelling was less sensitive to CaCl2concentration. There was some hysteresis in swelling between the wetting and drying cycles.The results are consistent with the swollen Ca‐montmorillonite being in the form of a tactoid, the arms of the tactoid consisting of the clay crystals aggregated end to end. Swelling is due to the development of double layers between crystals in the pores of the tactoid. The linkages at the joints of the tactoid arise because either there is perfect orientation between the crystals at these points or there is a small number of complex ions (≤ I m.e./100 g. clay) other than Ca‐ions present on the external surfaces of the crystals. CTA+ions, being strongly absorbed by the clay, increase the number of such linkages, so inhibiting double‐layer swelling. Whether or not Ca‐montmorillonites in general exhibit double‐layer swelling will depend critically on how many ions other than Ca‐ions are pre

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00679.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummayConcentric cones of whitened soil extend approximately 20 ft. below a termite mound in Southern Rhodesia. The pale colour is due to finely divided carbonates; the outer cone contains about 4 per cent. carbonates whilst the inner cone, riddled with termite galleries, has about 2 per cent. carbonates. The pH pattern shows highest values in the inner cone due to the presence of sodium salts. Termite activity thus gives rise to calcareous and sodium‐influenced soils in an area of leached ferrallitic soils.Physically, the soil below the mound has the same arrangement of horizons as the surrounding ferrallitic soils, namely, mineral material (M horizon), over a stone horizon (S horizon), over weathering granite (W horizon). The overlap of the inner cone and horizon W indicates that this arrangement of horizons has been brought about in part by termites carrying material up from the W horizon through the S horizon to the M horizon or mound at the surface.Termite activity has thus influenced both the pattern of salt distribution and mineral‐soil horiz

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00680.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryThe levels of added chloride and nitrate in the topsoil of a well‐drained red clay loam have been measured throughout two dry seasons and evidence obtained that a small upward movement of dissolved salt can occur. The extent of this movement was not, however, sufficient to account for the observed accumulation of nitrate in the surface soil and it is concluded that the greater part of this nitrate was produced by some other process, such as microbial activit

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00681.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryA comparison of the rate of wetting of aggregates taken from a virgin and continuously cultivated Red‐brown Earth has been made. The aggregates were placed on a glass sinter which was connected to a horizontal capillary. The rate of water uptake was obtained from the rate of meniscus travel as water was adsorbed from the sinter by the aggregates.When air‐dry (P/P0≊ 0·50) aggregates were wetted at 2 and 10 cm. water suction the cultivated aggregates wetted more rapidly than the virgin aggregates. At a suction of 30 cm. both groups of aggregates exhibited almost identical rates of wetting. The difference in the rate of wetting could not be attributed to differences in pore structure since both groups of aggregates had almost identical total porosity and clay content and furthermore showed extremely similar rates of wetting when wetted at a low suction with a non‐polar liquid. When aggregates from a virgin and cultivated soil were wetted slowly the pF‐water content relationship was very similar; it was therefore concluded that organic matter did not give rise to a finite contact angle for the water advancing into the virgin aggregates.Because the cultivated aggregates when wetted at 30 cm. and then at 2 cm. ion did suctnot slake when placed in water, whereas cultivated aggregates wetted directly to 2 cm. suction from the air‐dry condition slaked when placed in water, the phenomenon is described asincipient failure.When the cultivated aggregates are wetted at 2 cm. suction the work done by the rapid wetting causes planes of failure to be set up and the soil moves from an over‐consolidated condition to that represented by the n o d or virgin consolidation curve (Croney and Coleman, 1954). It is proposed that the organic matter in the virgin aggregates strengthens the pores against failure and so this material retains its initial pore structure. Mechanical strength measurements on virgin and cultivated aggregates support t

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00682.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY

摘要:

SummaryNon‐polar liquid (benzene and 1,1,2,2‐tetrachloroethane) content‐energy curves for soil aggregates have been obtained by using suction plate and pressure membrane apparatus (equivalent pF 0·5‐4·3). For low relative vapour pressure measurements a temperature differential was maintained between two connected chambers, one of which contained the soil aggregates and the other liquid benzene. The results are expressed as the volume of liquid retained in relation to the logarithm of the equivalent suction in centimetres of water (equivalent pF). This procedure enables a direct comparison to be made between the pF‐water content curves and the equivalent pF‐non‐polar liquid curve. When such comparisons are made for a number of clay soils it is apparent that 70 per cent. or more of the swelling takes place before pF 3 is attained on the wetting cycle. By differentiating the non‐polar liquid‐equivalent pF curves for a number of soil materials it has been possible to obtain the pore volume‐size distribution curves. All the clay materials gave broad peaks which extend between pF 2 and 4 and a small peak near pF 5. The peak which occurs just near pF 5 in clay soils is very pronounced for a loam soil. The peak in the coarse pore range occurs irrespective of origin and therefore appears characteristic of clay materials which have been through a number of wetting and drying cycles. The presence of this broad peak indicates that normal shrinkage cannot be expected for natural clay aggregates. The coarse pores which give rise to the broad peak can be regarded as structural pores which are eliminated by co

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1962.tb00683.x

出版商:Blackwell Publishing Ltd    

年代:1962

数据来源: WILEY