摘要:

SUMMARYThe minimum number of parameters required to model the unsaturated soil moisture characteristic, relating volumetric water content (θ) and matric suction (χ), is shown to be two. A third parameter, θ=θsat saturation, is required to define its saturation limit. The popular power‐function χ/χe, = (θ/θs)bis the most general three‐parameter model, with χ normalized by a notional air‐entry potential, χe. When log‐transformed, e.g. as In χ= a + bln(θ/θs), it gives a good fit to observations over varying ranges of χ. We show, using US, Australian, UK and NZ data, thata,band θs, in this formulation are uncorrelated across a wide range of textures, thus providing a ‘basis set’ of independent parameters. Gregson et al. (1987) used the alternative formulation In χ= a″+ bln(100θ), with χ rescaled to a percentage. Their reported correlation betweena″ andb, which led to their ‘one‐parameter model’ of the characteristic, is shown to be a mathematical artefact, arising from absorption

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe solid phases and the precipitation boundary characterizing the system H+‐Al3+‐oxalic acid‐silicic acid‐Na+are discussed. Model experiments have been used to throw more light on two environmental problems: the formation of sparingly soluble aluminium silicates in oceans and alkaline lakes, which could be determining aluminium and silicate concentrations in pore waters of sediments, and the validity of inorganic and organic mechanisms of podzolization and their significance for soil science.pH and Tyndallometric measurements were performed at constant ionic strength of 0.6 M NaCl at 25°C. Three phases Al(OH)4, H4SiO4(phase Via), Al2, (OH)6.H4SiO4(phase VIb) and NaAl(OH)4.(H4SiO4), (phase VIII) determine the precipitation boundary. Phase NaAl(OH)4.H4SiO4(phase VII precipitates at 0.4pH units above NaAl(OH)4.(H4SiO4)2. Using a set of previously determined binary and ternary complexes, and phases of the subsystems, the following formation constants were deduced:Phases VIaand VIbare described as end‐members of the allophane series with Si: Al ratios of 1:1 and 1.2. Phase VIbwas identified with protoimogolite allophane. These two phases are good model clays for podzolic soils and are extremely soluble at pH<4. Sodium phases could be hydrous feldspathoids. These phases are possible in sediments of seawater or saline lakes.It is suggested that organic and inorganic mechanisms of podzolization operate sequentially and that neither of them alone can completely describe t

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYSoil profiles from the Alltcailleach Forest in north‐east Scotland originally sampled in 1949/50 were resampled in 1987. Soil pH, exchangeable Ca, Mg, K and Na, extractable Al and cation exchange capacity were measured on the original stored and resampled soils. Chemical changes were characterized by decreases in pH, base cations, base saturation and cation exchange capacity. Extractable amounts of Al increased. Sequential leaching experiments showed a significant increase in the amount of extractable sulphate in mineral soil horizons.Changes in soil chemistry were interpreted to result from a combination of nutrient depletion caused by tree growth, natural pedogenic processes and atmospheric pollution effect

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe variation in the solubility of aluminium in some acid soils of south‐eastern Australia has been investigated. The hypothesis was that leaching of silicic acid influenced the extent of clay decomposition, and hence aluminium solubility, in accord with Le Chatelier's principle. In lower rainfall areas (1200 mm) it was consistent with gibbsite control. However, soluble silica concentrations were too high for gibbsite and kaolinite to be thermodynamically stable phases. The hypothesis was modified to take account of a quasi‐equilibrium in the open soil system, in which clay dissolution and A1 solubility appear to depend on the relative rates of H+input and of silica leaching. These may result in a supersaturated, or possibly even undersaturated system, at any point in time. The relative sizes of the organic sink and mineral Al source determine the influence of organic matter on Al solubil

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe effects of liming‐induced pH changes on surface charge were studied with four acid Fijian soils. All the soils possessed both positive and negative charge. Much of this charge was pH‐dependent, but some negative charge was present at pH values as low as 4.0 and small quantities of positive charge were detected at pH values as high as 8.2.Adsorption of phosphate (P) reduced positive charge at low pH and increased negative charge at high pH. The net amount of surface charge per unit of P adsorbed varied with pH and appeared to depend on the mineralogy of the s

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

SUMMARYThe sorption of phosphate (P) by four strongly acid Fijian soils from 0.01 M CaCl2decreased with increasing pH up to pH 5.5–6.0 and then increased again. The initial decrease in P sorption with increasing pH appears to result from an interaction between added P, negative charge, and the electrostatic potential in the plane of sorption. The results of a sorption study, involving KCl or CaCl2of varying concentrations as the background electrolyte and using Nadroloulou soil incubated with KOH or Ca(OH)2, suggested that the increase in P sorption at pH values>6.0 was caused by the formation of insoluble Ca‐P compounds. For some soils this is consistent with the results of an isotopic‐exchange study in which incubation with lime caused marked reductions in the amounts of exchangeable P at hi

ISSN:0022-4588    

DOI:10.1111/j.1365-2389.1990.tb00054.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY