摘要:

SummaryThe physics of land drainage is developed from the application of Darey's law to the water movement produced as a result of the conditions at the boundaries of the groundwater region in a given drainage situation. The physical understanding of the groundwater problem so obtained allows land drainage to be considered as an engineering operation founded on rational scientific principles and allows recommendations to be made concerning the design of installations. However, for theory to be applied in many field situations, a greater understanding of the soil‐water physics of heterogeneous soils, of fissured soils and of swelling soils is require

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00808.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe hypothesis that the specific surface of soil can be measured by water sorption is tested with data for 62 subsoils of widely differing origins. Ethylene glycol and water sorption at p/p0=0.47 are found to be very closely related measurements and both are highly correlated with CEC. Both methods give a satisfactory measure of total specific surface for soils classed as smectitic and having a large CEC. However, the application of the multilayer theory to the sorption of water on external surfaces of clayey soils with small CEC suggests that both sorbates overestimate the specific surface of such soils. A better estimate of the errors would be obtained from isotherm measurements with water, which is more suitable for this purpose than ethylene glycol.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00809.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryExamination of the previously published results of laboratory compression tests on a loam and a sandy loam has shown that as the water content and degree of saturation of a soil increase, the gradient of the virgin compression line, expressed in terms of specific volume and log of spherical pressure, increases and its intercept decreases. The water contents of the soils ranged from 5% to 30% and the degrees of saturation ranged from 10% to 40%. For both soils the gradient of the recompression line for previously compressed soils was shown to decrease with decreasing initial specific volume (increasing density) and to approach zero at a specific volume of 1.5 (dry bulk density of 1750 kg/m3). It was deduced that the position of the critical state line also varies with soil water content and that the critical state theory can be extended to unsaturated soils and therefore be of use in predicting the mechanical behaviour of agricultural soil during cultivation and compaction.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00810.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryTwo fluorescent dyes, sulpho‐rhodamine B and lissamine yellow FF, and three non‐fluorescent dyes, chlorantine fast green, sirius red and Chicago blue are compared for use in the identification of water transmission routes in structured soils. Subsequent to the flow of labelled water, a microsampling and extraction technique is employed to identify dye distribution in relation to structural features. The desirable properties of the dyes tested include stability over a wide pH range, anionic character and high molecular weight, the latter to reduce lateral diffusion from the transmission route. In these aspects they provide suitable alternatives to fluorescein and pyranine used by previous workers. The fluorescent dye lissamine yellow FF was found to be the most suitable for tracing rapidly moving water under field conditions. The transmission routes identified in field soils were associated with structural features readily recognized by routine soil survey techniq

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00811.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe pH‐dependence of surface charge density of three iron oxides and the clay fraction of five horizons of a variable‐charge soil has been studied by adsorption of potential‐determining ions (p.d.i.) and by adsorption of electrolyte ions. The general trend of results for iron oxides can be satisfactorily explained by a model which considers a three‐plane distribution of electric potential. When the model is applied to soil clays the outcome is less satisfactory and, although their charge properties seem to be largely determined by their high content of minerals with variable charge surfaces, the presence of minerals with a permanent charge (clay minerals) should be considered when explaining the particular data, even for those horizons where clay minerals are present in low prop

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00812.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe ‘Gaines and Thomas’ method for calculating the thermodynamic parameters of a cation exchange process has been criticized because equivalent rather than mole fractions were used in the definition of adsorbed ion activity coefficients. Although such coefficients are thus not theoretically correct, comparison with directly measured enthalpies of exchange shows that they indicate heterogeneity in the exchange process correctly. They also differ little from coefficients defined in terms of mole fractions. Such a re‐definition alters values of the thermodynamic equilibrium constant, and free energy and entropy of exchange by a constant factor, independent of cations and exchanger. Comparisons of series of cations, soils or clays using these parameters are therefore not aff

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00813.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryPeat samples representing depths of 0–15 cm and 15–30 cm were obtained from 11 upland sites in southern Scotland. Their pH, ash content, cation exchange capacity, phosphate sorption index and contents of 0.1mhydrochloric acid‐extractable iron and aluminium were determined as indicators of the extent to which phosphate and potassium ions would be retained following afforestation and application of fertilizers to these sites.In all soils cation exchange capacities were considerably larger than the quantity of potassium normally applied as fertilizer. Phosphate sorption indices were closely related to the content of extractable iron and aluminium in the peat samples. When expressed on a volume basis, the indices were low compared with those published for mineral soils, and some peats appeared to have almost no capacity to sorb phosphate ions from sol

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00814.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryCross polarization carbon‐13 nuclear magnetic resonance spectroscopy with magic angle spinning (CP‐MASS) was used to analyse for various forms of carbon in soils, a moss peat, hydrochloric acid insoluble residues from soils and peat, and litter from beech and pine trees. The chemical composition of the litters was also investigated by conventional techniques.The results show that hydrolysis with hydrochloric acid extraction removes nearly all oxygenated alkyl carbon from the soils used. It is shown that humification pathways in which carbohydrates are incorporated into humic substances via nonhydrolysable linkages are not important for the soils investigated in this work.CP‐MASS data suggest that the percentage of aromatic carbon in pine leaves increases with increase in ageing time. The results for the beech leaves are not sharply de

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00815.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummaryThe18O/16O ratios of a number of soil humic and fulvic acids were measured and compared with those of lignin and cellulose samples originating from the same area. The average enrichments above ground water were: cellulose 32%0humic and fulvic acid 29%0and lignin 14%0, suggesting that the oxygen in humic and fulvic acid originates pricipally from cellulose or other plant carbohydrates and not lignin as has been suggested.

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00816.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY

摘要:

SummarySoil from a field under long‐term grass was treated with 0.02msodium periodate for various periods up to 1176 h, followed by 0.1dsodium tetraborate for 6 h. This destroyed an increasing proportion of microaggregates>45 μm and carbohydrate. After periodate treatment for 6 h about 70% of the soil sugars remained in the residue as measured by reducing sugar content and about 67% as individual sugars measured by gas‐liquid chromatography. After 48 h the reducing sugar content was about 45%. An inverse linear relationship was established between the proportion by weight of microaggregates>45 μm and residual carbohydrate. The residual carbohydrate showed an enrichment in sugars commonly found in plant materials; glucose, arabinose and xylose, suggesting that the microbial carbohydrate had been preferentially destroyed. When the concentration of the periodate was increased to 0.05mthe residue contained about 50% of the original carbohydrate after 6 h treatment, and 25% after 48 h and an additional increase of about 10% in the proportion by weight of particles in the<45 μm range.These results throw doubt on the validity of assumptions made in a number of studies about the limited extent to which soil polysaccharide is involved in aggre

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1983.tb00817.x

出版商:Blackwell Publishing Ltd    

年代:1983

数据来源: WILEY