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The influence of microbial surfaces in the formation of short-range ordered aluminosilicates of allophanic composition was studied in the presence of citric, tannic and fulvic acids (FA) and two metals (Cd and Zn). In all bacterial cases, the pH was raised from an initial value of 4.5 to close to neutrality (6 to 7), and the bacteria produced a mineral phase in which a higher proportion of silicate...
Changes in tensile strength with clay type, clay particle size, and amounts of spontaneously and mechanically dispersible clays were assessed for dry, remoulded samples of eight Australian Vertisols and Alfisols varying in clay mineralogy. The effects of different clay content and particle size on tensile strength were also measured. The average particle sizes of whole clay, and of spontaneously...
The potassium supplying capacity of soils formed on three geological deposits along an east-west transect in the Niger Delta region of Nigeria was investigated by determining the various forms of soil K and K uptake by repeated maize croppings in pots. Soils (Inceptisols and Entisols) formed on recent alluvial materials of the Meander Belt deposits (MBD) had mica and feldspars resulting in very high...
Four large lysimeters on the San Dimas Experimental Forest, each filled with similar parent material and planted with monocultures of native species in 1946, provide a unique opportunity to quantify short-term effects of plant species on soil properties. The four species under which soils were investigated are scrub oak (Quercus dumosa Nutt.), chamise (Adenostoma fasciculatum Hook. and Arn.), ceanothus...
Soils with relatively sandy topsoils over clayey subsoils are widespread, but their genesis is not always clear. We tested the hypothesis that earthworms stimulate the formation of the sandy surface soils by producing clay-rich worm casts that are susceptible to erosion, in an undisturbed forested watershed in southwestern Ivory Coast. Soils of the watershed were strongly weathered and acidic. ...
The knowledge of the unsaturated hydraulic conductivity is one of the prerequisites to describe water flow and solute transport in soils. In this paper we examined the quality of 11 different theoretical models to predict the unsaturated hydraulic conductivity for a wide variety of soils. The hydraulic conductivity models were fitted to 44 measured curves using a quasi Newton parameter estimation...
Soil development, particularly in relation to relative age of geomorphic surfaces, was studied in a high-altitude valley on the semi-arid western side of the Andes in southern Peru. Seven major fluvial surfaces in the Colca Valley were recognized, including floodplains, stream terraces, and fans associated with the Rio Colca and its tributaries. Soils were also briefly examined on Pleistocene andesite...
Movement of mineral dust by the atmosphere has been underway for ages, but efforts to assess its magnitude and significance have come largely in the last century. Attempts to identify and understand effects of the dust on soils are even more recent, mostly in the last 30 years. Airborne movements have several forms. Dust is transported by large storms that can be spectacular. Dust is also moved...
Modern soils in south-central Nebraska may have formed in parent material made up of more than one loess unit. The aerial extent of these soils could be as much as 1.6 million ha. The presence of lithologic discontinuities within these soils complicates the explanation of their genesis. The objectives of this study were to determine if multiple loess units exist in the modern soils and to identify...
The distribution of calcitic pedofeatures within part of a buried paleosol complex on Gaolanshan Mountain, near Lanzhou in the western semi-arid part of the Loess Plateau of China, is interpreted in terms of a pedosedimentary model controlled by changes in dominance of regional climatic (monsoonal) forces. During periods of moderate loess accumulation rates and moisture availability, accretionary...
Increased soil organic matter (SOM) is associated with a reduction in K fixation by a calcareous vermiculitic soil in California. To better understand the mechanism for this effect, humic acids (HA) were extracted from this soil with and without decalcification. The HA extracted without decalcification -- the mobile HA (MHA) pool -- was dated as modern by 14 C-dating, while the radiocarbon...
The spatial variability of soil properties in a typical volcanic Vesuvian soil was investigated by collecting undisturbed soil samples at equal intervals of 1.5 m along a 135 m transect at a depth of 0.45 m. In this study, the spatial structure of soil hydraulic properties was examined using both statistical and geostatistical concepts. Soil hydraulic properties were determined in the laboratory...
Humification is one of the dominant pedogenic processes responsible for the development of Mollisols but systematic studies of humic acids in the whole sola were rarely documented. To further understand this process, humic acids were extracted from sola of two Mollisols in central Alberta with 0.1M Na 4 P 2 O 7 and analyzed in our laboratory. Humic acid yields decrease abruptly...
The predominant methods of measuring soil structural stability are confined to laboratory methods that, by their nature, do not quantify the field stability of the soil. An instrument is presented here for measuring the soil structural stability in situ. Stability is assessed by a method based on the change in structural characteristics that may occur when the soil is permeated by non-interactive...
In the Tamoa Valley, on the western coast of New Caledonia, a Vertisol sequence shows a downslope transition from calcimagnesic Vertisols containing gypsum, aragonite, and magnesium-calcite, derived from flysch colluvium, to hypermagnesic Vertisols, rich in dolomite and magnesite, and derived from peridotite and serpentinite alluvium deposited by the Tamoa River.Gypsum, magnesium-calcite and magnesite...
We evaluate data from a chronosequence study of landslide scars, ranging in age from 1-55+ yr, in the Luquillo Experimental Forest (LEF) a subtropical lower montane wet forest (sensu Holdridge) in eastern Puerto Rico. Surface mineral soil (0-10 cm) base saturation index (BSI) values increase during primary succession in the LEF (R=0.85, P<0.001). Both BSI values and major nutrient cation concentrations...
P-sorption isotherms were determined for calcium carbonate (AR grade) and four soils, which contain various amounts of iron oxides and calcium carbonate. The results could be put into the Langmuir equation. The sorption maximum of calcite was 26 mg P kg -1 . This result was used to calculate the surface coverage of calcite by sorbed P. The model indicated that only 14 to 18 of the...
In this study, the depth distribution of organic carbon (OC) content in a sandy soil was characterized for a small agricultural plot (1.5 ha). The means and the distributions for measured OC were used as sorption-related parameters in a solute transport model to predict the movement of the herbicide atrazine in the unsaturated zone. Simulations were performed in order to assess the impact of OC...
Mapping rules based on the knowledge of regional soil patterns -- soil pattern rules -- can be acquired from a previous soil survey of a small but representative sample area called the reference area. They can then be used in new soil surveys carried out on wider areas; this allows both to select the observation points and to predict which soil unit occurs at non-observed points. A quantified formulation...
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