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  • 11
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Books reviewed in this article:Ballif, J.-L., Guérin, H. and Muller, J.-C. Eléments ?agronomie Champenoise. Connaissance des sols et de leur fonctionnement. Rendzines sur craie et sols associésOllier, C. and Pain, C. Regolith, Soils and LandformsSchwab, G.O., Fangmeier, D.D. and Elliott, W.S. Soil and Water Management SystemsVelde, B. (Ed.) Origin and Mineralogy of Clays; Clays and the Environment
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  • 12
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The analysis of free lipids in 12 soils from three representative types of Mediterranean forest has been carried out in an attempt to describe diagnostic molecules reflecting differences between the ecosystems and the intensity of the soil organic matter turnover. The study centred on the analysis by gas chromatography–mass spectrometry of the soil compounds extracted with petroleum ether from soils in central Spain, developed under monospecific formations of stone pine (Pinus pined), evergreen oak (Quercus rotundifolia) and Spanish juniper (Juniperus thurifera), the lipid extracts from their leaves also being analysed as reference material.The comparison between the distribution patterns of alkanes and fatty acids in plant lipids and the corresponding soil lipids was used to assess the extent to which the former accumulate in soil or are substituted by other biogenic or diagenetic homologues. In general, the alkane patterns showed the greatest variation in soils under oak, and the differences between lipid patterns in plant and soil were greatest in the juniper forests. As indicators of the vegetation type, the soil fatty acids had little value.Up to 60 major cyclic compounds were identified, including mainly di- and sesquiterpenes, in addition to some monoterpenes and nonterpenic naphthalenes and decalins. Of these major constituents, 33 compounds were found in soil but were not present in plant extracts, and 18 compounds were identified in plants but were not in the soils. The results suggest an arrangement of the soil samples based on the composition of the signature lipid assemblages.
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  • 13
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The basic principles of the electrophoretic behaviour of humic substances (HS) still need to be systematically investigated. HS extracted from a Cryorthod (HS–1) and from an Haplumbrept (HS–2) were first fractionated by ultrafiltration to obtain two series of fractions of reduced polydispersity with a nominal mean relative molecular mass (M) of 7500, 20000, 40000, 75000 and 200 000 Da. Fractions extracted from the same soil behaved like an homologous series when tested by size exclusion chromatography, showing a linear relation of M with molecular size. When plotted against their mean M, the elution volumes of HS fractions extracted from the two different soils originated lines of different slope. Absolute electrophoretic mobilities of the fractions were determined in polyacrylamide gel slabs of increasing polyacrylamide concentration using a single buffer system; in all gels there was a close linear relation between the electrophoretic mobility and the logarithm of the mean M of HS fractions. Extrapolation of mobilities of HS–1 at zero gel concentration gave intercepts that did not differ significantly, showing that there was a constant mobility for all fractions in free solution. These results mean that charge differences have little effect on the electrophoretic mobilities of HS extracted from the same soil and imply the theoretical possibility of determining M distributions of HS by polyacrylamide gel electrophoresis in a single buffer system. Mobilities of HS–2 fractions were compared with those of HS–1: the latter fitted the regression equations of mobility against logarithm of the molecular weight obtained from HS–1 humic substances only in gels of small acrylamide concentration. Deviations were larger at small M, probably because of the increasing fulvic character of the fractions, and increased in gels of greater acrylamide concentration, indicating that charge differences may not be negligible when comparing humic substances extracted from different soils.
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  • 14
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: We studied the sorption of phosphate and oxalate on a synthetic aluminium hydroxysulphate complex and the associated release of sulphate from this complex. In the pH range 4.0–9.0 the presence of phosphate or oxalate tended to increase the release of sulphate. Much more phosphate than oxalate was sorbed, but in most cases oxalate caused more removal of sulphate than did phosphate. Only in acid systems may these results be partly attributed to the greater solubilization of the complex in the presence of oxalate than in the presence of phosphate. At pH 〉 8.0 in the presence of phosphate, and at pH 〉 6.5 in the presence of oxalate, the quantities of sulphate replaced were greater than the quantities of phosphate or oxalate sorbed, suggesting that hydroxyl ions competed with phosphate and oxalate for sorption sites and sulphate removal. Sulphate was only partly removed from the complex even after repeated washings with phosphate or oxalate solutions or after 120 h in the presence of these ligands at pH 6.0. When phosphate and oxalate were added as a mixture much more phosphate than oxalate was retained. Phosphate strongly inhibited oxalate sorption, whereas oxalate partly prevented phosphate sorption only at pH 〈 7.0. More sulphate was removed in the presence of both the anions than in the presence of phosphate alone, but less than that desorbed in the presence of oxalate alone.
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  • 15
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The adsorption of isoproturon on soil and pure clay minerals has been investigated as a means of understanding its mobility in soils. Measured adsorption coefficients are correlated with soil and clay mineral properties.Soil organic matter controlled the adsorption of isoproturon at organic carbon contents exceeding 27 g kg−1, whereas at less than this threshold, clay mineral surfaces appeared to control adsorption. The effect of varying temperature suggests that adsorption of isoproturon is a physical process. From the comparison of the fits of linear, Freundlich, and Langmuir adsorption isotherms to the data, the adsorption is best described as a partition process.
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  • 16
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A review of water retention functions based upon fractal soil structures is presented. We consider the modelling approach for a fractal fabric, a fractal pore boundary and a fractal pore space, identifying the latter case as one of particular complexity. In each case, the water retention function is derived from the pore volume distribution arising from the structural model in question. We examine published models and highlight problems, namely lack of generality and inconsistency with the assumed fractal structure. The models considered in this paper do not account for the effects of pore connectivity, and as such their validity as a necessary condition for the existence of fractal structure is questionable.
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  • 17
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Single rainfall events play an important agricultural and ecological role, especially in dry regions where precipitation is erratic. Infiltration, redistribution and evaporation of single quantities of water are important in this context and have been investigated in the laboratory.Three soils of differing texture were packed at two uniform initial water potentials (– 100 MPa and –1.5 MPa) into columns, after which 12.7, 25.4 and 50.8 mm of water were applied as a single irrigation. The columns were maintained in a controlled hot and dry atmosphere (evaporativity = 16.7 mm d-1) for up to 30 days, during which water-content profiles were measured at intervals.Infiltration was rapid to depths ranging between 35 and 250 mm. Thereafter redistribution was small. Evaporation caused the water profile to develop three zones: dry between the soil surface and the drying front, dry below the wetting front, and an intermediate wetter zone between the drying and wetting fronts. As evaporation continued, the drying front moved deeper into the soil and the water content in the intermediate zone decreased.During the first few hours evaporation was rapid and constant, at the evaporativity of the atmosphere. Subsequently, evaporation was slower. Total evaporation (E) increased with time (t) as Eα tn for t 〉 1 d, where n = 0.24 for a loamy sand, 0.33 for a clay loam and 0.31 for a silty clay loam.Weighted-mean soil-water diffusivities, averaged over the profile above the wetting front, ranged between 1000–2000 mm2 d−1 at the start of the falling-rate stage and 200–400 mm2 d−1 near air-dryness, in reasonable agreement with the few results in the literature.
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  • 18
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: In the Congo, near Pointe-Noire, Pinus and Eucalyptus were planted on the savanna for 30 years. We have characterized the effects of this change on land-use on the composition of carbohydrates in whole soil and particle-size fractions of the soil. Carbohydrates represent variable proportions of the total soil organic carbon (TOC) of various particle size fractions. The largest proportions of sugar-C were found in the savanna soil with as much as 250 mg g−1 TOC in the coarsest plant remains and approximately 190 mg g−1 TOC in the finest organo-mineral fractions, whereas there was always less sugar in plantation soils. The monosaccharide xylose and mannose have different distributions: xylose appears to be the marker of the vegetal inheritance, whereas the dominance of mannose in the clay fraction bears the signature of current microbial sugar synthesis.The quantitative and qualitative evolution of the whole soil carbohydrates was studied as a function of plantation age. Carbohydrate-C represents 131 mg g−1 of the soil organic carbon in the savanna soil, but decreases to an average value of 75 mg g−1 in plantations more than 6 years old. This appears to be due mainly to the stimulation of the mineralization of the glucose, which represented 60% of the total sugars in savanna soil and only 45–48% in tree plantations. The ratio [arabinose + galactose + fucose]/[rhamnose + xylose], which is the largest in the oldest plantations, is significant for evaluating the replacement of carbohydrates of the original grass savanna by those of the trees.
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  • 19
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Organically-bound Al in acidic, base-poor sandy soils seems to be a major contributor to dissolved Al. This hypothesis has been tested under field conditions at two intensely acidified sites. The research was conducted at the agricultural trial fields at Lyczyn, Poland, which have been fertilized continuously for 30 yr with 130 kg ha−1 a−1 N (as NH4NO3 or urea). The effect of depletion of Al on its solubility was also studied.Field data confirmed that mobilized Al originates largely in the organically bound fraction of soil Al. Depletion of this fraction resulted in a considerable decrease in the mobility of Al such that, at pH = 3.0 and reaction times of a few weeks, small amounts of Al were mobilized. Apparently, the rate at which Al is dissolved from structural silicates, which are abundant in the soil investigated, is small. This suggests that at sites in Poland most exposed to acid deposition, where the rates of soil acidification and depletion of organically-bound Al are greatest, both the concentration of Al and the soil solution pH are expected to decline with time.
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  • 20
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1365-2389
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Radioactive caesium deposited on upland Britain following the Chernobyl accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentration of Cs+ required to cause Cs+ fixation is 0.60 to 0.75 mm, and this is unlikely to be reached in any contaminated upland soil. It is suggested that the fixation is caused by interlayer collapse of the illitic clay. The observed Cs+ fixation in lowland mineral soils and its absence from acidic upland soils is explained by the action of K+ ions, which can also induce interlayer collapse.Although Cs+ ions are unlikely to be fixed in acid organic soils, they can be strongly sorbed on any unoccupied Cs-specific sorption sites in the narrow parts of illitic wedge zones. A method for determining the number of such sites is described. For two of the soils studied the number of sites ranged between 8 × 10−8 and 1 × 10−5 mmol kg−1; for two others there appeared to be no unoccupied Cs-specific sites. Although Cs+ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the concentration of Cs+ in solution is decreased. Thus, radioactive Cs in such soils will remain available for plant uptake, unless interlayer collapse can be induced.
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