摘要:

SummaryThe fundamental objective of soil classification is the achievement of an agreed world–wide system of maximum usefulness to the widest possible range of users. Such a classification should be natural rather than artificial because soils are natural bodies. Further, it should be hierarchical rather than co–ordinate because hierarchies are readily comprehensible and memorable, can be constructed on the basis of a few characters, and do not need to give equal weight to all criteria used in classifying soils. They also have the advantage of closely denned, mutually exclusive classes which can still make allowance for occasional aberrant profiles or pedons.The historical development of soil classifications is discussed with particular reference to the Russian and French and especially the U.S. Dept. Agric. 7th Approximation. The latter is defended against the main criticisms that have been levelled against it. It is maintained that it has been desired by sound inductive as well as deductive reasoning, that it treats soils as polythetic individuals, that it considers pedons three–dimensionally and that it permits non–hierarchical sub–classifications. Attention is given to the more practical criticisms that there is an undue emphasis on soil moisture and temperature regimes, unknown genetic criteria and the shallower horizons, and that it handles ses‐quioxidic soils inadequately. Positive advocacy is made on the ground that the 7th Approximation will facilitate and speed soil research especially in developin

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02307.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryMull and mor humus can be distinguished in freely drained British surface soils by the pyrolysis products derived from whole soil samples. About i milligram of soil is pyrolysed at 770 °C in a Curie point apparatus and a sample of the volatile decomposition products is allowed to enter a low‐resolution mass spectrometer. A numerical value (the ‘Discriminator Value’) which will discriminate between the two humus types is then calculated from the spectrum of each sample. This is performed by multiplying the intensity of each mass peak by a weight factor and then summing the weighted intensities up to mass 110The weight factors are obtained empirically by taking sets of spectra from clearly distinguished mull and mor samples and applying a computerized learning machine procedure. Once obtained, they are relatively easily applied to spectra from other soils.The method places all samples on a numerical scale on which mull types appear positive up to about 20 × 108and mor types negative down to about ‐15 × 103, intermediate types being recognized in about the middle of the range. It is indicated that the most important pyrolysis products active in the discrimination process are the olefin hydrocarbons, particularly ethylene, which are produced in greater abundance from

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02308.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryA farmer (or other users of land) achieves greatest net return by using each soil for the crop and management which gives maximum return.A soil map indicates the boundaries between soils requiring different management for optimum returns. The benefits from a soil survey increase with the ‘purity’ of the soil units as mapped.The cost of soil survey increases sharply with the ‘purity’ to be achieved. So it is necessary to recognize the stage beyond which the costs of yet more detailed soil survey are unlikely to exceed the benefits to be expected from mapping units of greater ‘purity’.This paper reports a simple algorithm for calculating the probable benefits from further soil survey to produce a map of higher ‘purity’ than

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02309.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummarySamples from fifteen salt crusts from the central Great Konya Basin, Turkey, were studied in the laboratory. Chemical analyses data were combined with the results of X‐ray diffraction.In the mineralogical systems studied, three types of salt efflorescences of different morphology were distinguished, with mirabilite/thenardite, bloedite, and bloedite/epsomite/halite as major mineral associations. These crusts seal the surface soil more or less effectively, thus reducing evaporation and thereby preventing cracking of the saturated soils. The effectiveness of this sealing depends on the morphology of the accumulated salt minerals rather than on their chemical composition. Reclamation of salt‐encrusted spots therefore requires understanding of the mineralogy and the morphology of the efflorescent sa

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02310.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryAdsorption isotherms were determined for the specific adsorption of copper by soils and soil constituents. Adsorption was found to conform to the Langmuir equation. The Langmuir constants,a(adsorption maximum) andb(bonding term), were calculated. Soils were found to have specific adsorption maxima at pH 5.5 of between 340 and 5780 μg g−1, and a multiple regression analysis revealed that organic matter and free manganese oxides were the dominant constituents contributing towards specific adsorption. Adsorption maxima for soil constituents followed the order manganese oxides>organic matter>iron oxides>clay minerals, which supported the findings for whole soils.The cation exchange capacities (non‐specific adsorption) of the test soils were found to be far greater than the specific adsorption maxima. However, evidence suggests that, for the relatively small amounts of copper normally present in soils, specific adsorption is the more important process in controlling the concentration of copper in the soil solu

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02311.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryTwo distinct forms of ochre are known to occur in field drains. One form, which is most common in wet peaty areas, is caused by the growth of filamentous iron bacteria. The second form is associated withThiobacillus ferrooxidans, and occurs where the soil contains pyrite.Contrary to previous reports, liming decreases the rate at which pyrite is oxidized in soil and, by decreasing the amount of iron entering the drains in a given period, should significantly increase the active life of the drainage system. Regular liming is probably preferable to a single large initial dressing.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02312.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryWater profiles in soil columns were measured by the single‐source gamma radiation method. Together with the normal attenuation equation, linear or parabolic equations for the relation between bulk density and volumetric water content were used. To compensate for moderate changes in the bulk density during the experiment both initial and final bulk density and the water content were used in the water profile estimations.For a sandy loam soil, the radiation method without any corrections for bulk density changes resulted in a mean error of the volumetric water content estimation of 0.035 cm3cm−3, when the water content changed from 0.35 to 0.15 cm3cm−3. By correction for changing bulk density by means of a linear or a parabolic equation the maximum difference between real and estimated water content was 0.009 and 0.002 cm3cm−3, respectively. Applying the latter method and a count of 105the error of a single water content measurement was 0–00

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02313.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryMeasurements of unconfined shear strengths were made over a range of moisture contents on seven remoulded agricultural soils which covered a range of textures, and these were used to calibrate the Swedish fall‐cone device. It was found that the calibration factor, usually regarded as constant in engineering literature, was dependent on soil texture, but constant over a range of moisture contents for a given soil texture.From the assumption that the liquid and plastic limits correspond to two fixed specified strengths, it is shown that one can use the fall‐cone device to determine these limits by making measurements of cone penetrations over a range of moisture contents. It is suggested that a modified plasticity chart, which can be obtained very simply from measurements of cone penetrations made over a restricted range of moisture contents, may be used for characterizing soil behavi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02314.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummaryWhen API‐9 kaolinite and Willalooka illite clays were mixed in various proportions, the pore‐size distributions obtained using nitrogen sorption and mercury injection techniques were found to be characteristic of neither of the components but showed a progressive reduction in the pore size as the concentration of illite was increased. The plate separation of the mixtures showed a marked decrease with initial added illite, approaching that of the illite when the mixture contained approximately 40 per cent illite. This is indicative of a homogeneous mixture in which the fine illite particles fill in the pores bounded by the relatively coarse kaolinite particles.The relationship between particle dimensions (derived from crystallographic parameters and specific surface area) and pore size of single clays and clay mixtures is consistent with a model in which slit‐shaped pores result from the parallel interleaving of clay crystals for the single clays. Some deviations occur for the mix

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02315.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY

摘要:

SummarySoil compression is caused in agriculture by tillage implements, plant roots, treading by animals, and by wheels and tracks of vehicles. Increases in soil density resulting from compression usually reduce crop growth and yield.Compression and expansion of samples of five remoulded soils, each at several moisture contents, were investigated. Soil samples were subjected to isotropic stress of up to 3.5 MN m−2in a pressure cell. Volume changes were measured by the volume of pore fluid effused or infused through one of the sample surfaces.Particle packing densities,D, were well described by the equationwhereD0is the maximum limiting value ofD, Pis the applied isotropic stress, andB, C, K, Lare adjustable parameters. One of the exponential terms in this equation describes deformation of soil crumbs and the other describes rearrangement of individual particles.Two sample sizes gave similar values for the equation parameters. A small increase in moisture content results in a large increase in soil compressibility. It is hypothesized that resistance to compression may be one of the principal influences in the mechanical restriction of root growt

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1973.tb02316.x

出版商:Blackwell Publishing Ltd    

年代:1973

数据来源: WILEY