Search Results (9)

The geological study area is volcano-tectonic in nature. Microscopic observations and mineralogical analyses revealed the presence of allophane and diatom clusters whose mineral compositions coincided with weathered andesites and dacites. Edometric consolidation tests showed a high porosity and a reduction in the void ratio by up to five times. These are highly compressible soils with a Cc/Cs ratio of 12 to 15 and a specific gravity (Gs) of 2.4. Low initial bulk density (1.10 Mg/m³), high plasticity, and SUCS (OH) classification are typical of soft soils, with an effective friction angle (ɸ’C_D) of 25.5° to 30° and effective cohesion (c’_CD) of 11.90 to 47.27 KPa. The shear wave velocity for the first 10 m (Vs10) on average ranged from 78 m/s to 120 m/s, whereas that for the first 30 m (Vs30) was 169 m/s. The permeability, which was calculated indirectly, was between 2 × 10⁻⁷ and 3 × 10⁻⁸ m/s. With an organic matter content between 5% and 25%, the Caupicho soil is an organic mineral sediment that is not considered peat (non-peat). The results of this study serve as a basis for future analyses of soil dynamics, bearing capacity, and consolidation settlements in the medium and long term in an area of high urban growth in southern Quito, Ecuador. Full article

The Somma–Vesuvius volcanic complex emitted huge quantities of volcanic materials over a period from before 18,300 years BP to 1944. The activity during the last period, from post-AD 1631 to 1944, primarily produced lava and pyroclastics via effusive and strombolian eruptions. We investigated the pedogenesis on rocks formed from post-AD 1631 to 1944, occurring on the slopes of Mt. Vesuvius up to Gran Cono Vesuviano and in the northern valley separating Vesuvius from the older Mt. Somma edifice. Pertinent morphological, physical, chemical, and mineralogical (XRD and FT-IR) soil properties were studied. The results indicated the existence of thin and deep stratified soils on lava, as well as the presence of loose detritic covers formed via pyroclastic emplacement and redistribution. The soils showed minimal profile differentiation, frequently with layering recording the episodic addition of sediments. We found that the dominant coarse size of primary mineral particles was preserved, and there was a low level of clay production. The main mineralogical assemblage present in sands also persisted in clays, indicating the physical breaking of the parent material. Chemical weathering produced mineral modifications towards the active forms of Al and Fe and was also attested in selected soils by glass alteration, allophane production, and the presence of analcime in clay as a secondary product from leucite. The differences in glass alteration and analcime production found in the selected soils on lava were related to soil particle size and soil thickness. Concerning the youngest soil present on Gran Cono Vesuviano, other factors, such as the substratum’s age and site elevation, appeared to be implicated. Full article

The application of Cd-contaminated phosphate fertiliser has enriched concentrations of this non-essential element in many agricultural soils. Consequently, concentrations of the metal in some agricultural products exceed the Maximum Limit in foods. Composts can reduce the transfer of Cd from soil to plants; however, it is unclear how long this beneficial effect endures. We aimed to determine temporal changes of phytoavailable Cd in two market garden soils (an Allophanic Orthic Granular Soil and a Recent Silt Loam). Soils were amended with either municipal green waste compost or sawdust and animal waste compost at a rate of 2.5% w/w under three incubation regimes: at 19 °C, at 30 °C, and at 30 °C with additional N added as urea at 0.6 g urea/kg soil added over 1 year. Each replicate was sampled after 1, 5, 9, 13, 21, 31, and 49 weeks, and phytoavailable Cd was estimated through 0.05 M Ca(NO₃)₂ extraction. Seed potato (Solanum tuberosum), ‘Nadine’ variety, was grown in the Pukekohe Allophanic Orthic Granular Soil, freshly amended with municipal compost and the same soil aged for one year. The concentration of Cd in all samples was analysed using an ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The C concentration in the soil—compost mixtures decreased over the year, with the greatest decreases occurring in the soils incubated at 30 °C with added N. Unexpectedly, the concentration of Ca(NO₃)₂-extractable Cd in the compost-amended soils did not increase over time and in some cases even decreased. This was confirmed through a pot experiment, which showed the Cd concentration in potato was reduced by 50% in both the freshly amended soil and the amended soil aged for one year. Cadmium immobilisation in soils might be due to both the sorption of Cd by organic matter and the occlusion of sorbed Cd by oxy-hydroxides of iron and aluminium. Over 49 weeks, soluble Cd does not increase as organic matter oxidises. The application of municipal compost to soil will reduce both plant Cd solubility and plant Cd uptake for at least one year in the soils tested. Full article

Andosols are characterized by high organic matter content and play a significant role in carbon storage. However, they have low phosphorus fertility because of the high phosphate-fixing capacity of active aluminum. For agricultural use of Andosols, it is necessary to ameliorate its poor phosphorus fertility by applying lime and high doses of phosphate fertilizers. The objective of the present study was to clarify how such soil amendments affect the mineralization of soil organic carbon (C) and nitrogen (N) in allophanic Andosols under different temperature regimes. The soil was treated using combinations of liming and heavy phosphate application, followed by incubation under different temperature conditions. The N mineralization and the soil CO₂ evolution rate were measured periodically. The patterns of N mineralization were analyzed by fitting them to first-order kinetics. Liming increased C and N mineralization irrespective of temperature, and the increase was further enhanced by phosphate application. Kinetic analysis of the N mineralization curve indicated lowering of the activation energy of N mineralization reactions with phosphate application, suggesting that P application may accelerate N mineralization at lower temperatures. These findings provide a basis for developing soil management strategies to reduce the loss of soil organic matter. Full article

For thousands of years, the volcanic activity present along the Andes Mountain range has generated a large amount of pyroclastic material. As a result, around 60 percent of the soils present in Chile have a volcanic origin, of which, we can find soils derived from volcanic ash. These correspond to soils whose origin is the weathering of volcanic ash, which generates minerals such as allophane, imogolite, and halloysite. The presence of these minerals gives these soils unique geotechnical properties, such as high plasticity, low dry unit weight, and a unique internal structure. Subjecting these soils to extreme temperatures like those needed to perform standard laboratory tests produces changes in their structures, and thus in their geotechnical behavior. These changes are important to be aware of with respect to slope stability problems, embankment conformation, surface foundations, etc. In the present study, a type of soil found in Chile originating from the weathering of volcanic ash and locally named Trumao was studied. Due to its age and formation processes, the main minerals found in the soil are allophane and imogolite, and hence it belongs to the allophanic soil type. The material was studied in its natural state (undisturbed) and, after being oven-dried using common geotechnical tests, the behaviors of both samples were compared. The study shows that some properties are affected significantly by the oven-drying process, and thus it is not recommended to expose the material to high temperatures during geotechnical laboratory testing to avoid misleading results. Full article

Silicon (Si) is found in various fractions of soil, depending on the pedogenic processes of the environment. Dissolved Si (DSi) is adsorbed in soil particles or leaches through the soil profile into the groundwater. The objective of this study is to quantify, using the sequential extraction method, the different Si fractions in volcanic ash soils on Jeju Island that may affect groundwater Si content, and to compare them with those in forest soils on mainland Korea. Most of the Si in these soils was bound in unavailable forms as primary and secondary silicates. The second largest proportion of Si in the non-Andisols of Jeju Island and Korean mainland soils was accumulated as amorphous Si, while in the Andisols of Jeju Island, the second most significant Si fraction was in pedogenic oxides and hydroxides. The products of these soil formations were short-range-order minerals such as allophane (4–40%). The adsorbed Si concentration tended to increase at lower depths in Andisols (100–1400 mg kg⁻¹) and was approximately five times higher than that in non-Andisols. The results indicate that Si is more soluble in the Andisols of high precipitation regions and that Andisols on Jeju Island potentially affect groundwater Si concentration. Full article

In this article, I show how an Ultisol, representative of a globally-important group of soils with clay-rich subsoils, low base saturation, and low fertility, in the central Waikato region in northern North Island, can be evaluated using soil stratigraphy and tephrochronology to answer challenging questions about its genesis, age and classification. The Kainui soil, a Typic Kandiudult (Soil Taxonomy) and Buried-granular Yellow Ultic Soil (New Zealand Soil Classification), occurs on low rolling hills of Mid-Quaternary age mainly in the Hamilton lowlands in, and north and northeast of, Hamilton city. It is a composite, multi-layered tephra-derived soil consisting of two distinct parts, upper and lower. The upper part is a coverbed typically c. 0.4–0.7 m in thickness (c. 0.6 m on average) comprising numerous late Quaternary rhyolitic and andesitic tephras that have been accumulating incrementally since c. 50 ka (the age of Rotoehu Ash at the coverbed’s base) whilst simultaneously being pedogenically altered (i.e., forming soil horizons) via developmental upbuilding pedogenesis during Marine Oxygen Isotope Stages (MOIS) 3-1. Any original depositional (fall) bedding has been almost entirely masked by pedogenic alteration. Sediments in lakes aged c. 20 ka adjacent to the low hills have preserved around 40 separate, thin, macroscopic tephra-fall beds mainly rhyolitic in composition, and equivalent subaerial deposits together form the upper c. 30 cm of the coverbed. Okareka (c. 21.8 ka), Okaia (c. 28.6 ka), Tāhuna (c. 39.3 ka) and (especially) Rotoehu tephras make up the bulk of the lower c. 30 cm of the coverbed. Tephra admixing has occurred throughout the coverbed because of soil upbuilding processes. Moderately well drained, this upper profile is dominated by halloysite (not allophane) in the clay fraction because of limited desilication. In contrast, Otorohanga soils, on rolling hills to the south of Hamilton, are formed in equivalent but thicker (>c. 0.8 m) late Quaternary tephras ≤c. 50 ka that are somewhat more andesitic although predominantly rhyolitic overall. These deeper soils are well drained with strong desilication and thus are allophanic, generating Typic Hapludands. Ubiquitous redox features, together with short-lived contemporary reduction observed in the lower coverbed of a Kainui soil profile, indicate that the Kainui soil in general is likely to be saturated by perching for several days, or near saturation for several months, each year. The perching occurs because the coverbed overlies a slowly-permeable, buried, clay-rich paleosol on upper Hamilton Ash beds, >c. 50 ka in age, which makes up the lower part of the two-storeyed Kainui soil. The coverbed-paleosol boundary is a lithologic discontinuity (unconformity). Irregular in shape, it represents a tree-overturn paleosurface that may be c. 74 ka in age (MOIS 5/4 boundary). The buried paleosol is markedly altered and halloysitic with relict clay skins (forming paleo-argillic and/or paleo-kandic horizons) and redoximorphic features. It is inferred to have formed via developmental upbuilding pedogenesis during the Last Interglacial (MOIS 5e). The entire Hamilton Ash sequence, c. 3 m in thickness and overlain unconformably by Rotoehu Ash and underlain by c. 340-ka Rangitawa Tephra at the base, represents a thick composite (accretionary) set of clayey, welded paleosols developed by upbuilding pedogenesis from MOIS 10 to 5. Full article

Mechanisms of protecting soil carbon (C) are still poorly understood despite growing needs to predict and manage the changes in soil C or organic matter (OM) under anticipated climate change. A fundamental question is how the submicron-scale interaction between OM and soil minerals, especially poorly-crystalline phases, affects soil physical aggregation and C stabilization. Nano-sized composites rich in OM and poorly-crystalline mineral phases were presumed to account for high aggregate stability in the Andisol we previously studied. Here we searched for these nanocomposites within a sonication-resistant aggregate using scanning transmission X-ray microscopy (STXM) and near-edge X-ray absorption fine structure (NEXAFS) as well as electron microscopy (SEM, TEM). Specifically, we hypothesized that nanometer-scale spatial distribution of OM is controlled by poorly-crystalline minerals as both co-exist as physically-stable nanocomposites. After maximum dispersion of the cultivated Andisol A-horizon sample in water, one aggregate (a few µm in diameter) was isolated from 0.2–2 µm size fraction which accounted for 44–47% of total C and N and 50% of poorly-crystalline minerals in bulk soil. This fraction as well as <0.2 µm fraction had much higher extractable Al and Fe contents and showed greater increase in specific surface area (N₂-BET) upon OM oxidation compared to bulk and >2 µm size fractions, implying high abundance of the nanocomposites in the smaller fractions. The isolated aggregate showed a mosaic of two distinctive regions. Smooth surface regions showed low adsorption intensity of carbon K-edge photon energy (284–290 eV) with well-crystalline mineralogy, whereas rough surface regions had features indicative of the nanocomposites: aggregated nanostructure, high C intensity, X-ray amorphous mineral phase, and the dominance of Si, O, Al, and Fe based on SEM/EDX and TEM/EDX. Carbon functional group chemistry assessed by NEXAFS showed the dominance of amide and carboxyl C over aromatic and aliphatic C with some variation among the four rough surface regions. Together with C and N isotopic patterns among the size fractions (relatively low C:N ratio, high ¹⁵N natural abundance, and more positive Δ¹⁴C of the <2 μm fractions), our results provided the direct evidence of preferential binding of microbially-altered, potentially-labile C with poorly-crystalline mineral phases at submicron scale. The role of the nanocomposite inferred from this study may help to bridge the knowledge gap between physical aggregation process and biogeochemical reactions taking place within the soil physical structure. Full article

The effect of fluctuating soil moisture cycles on soil cadmium (Cd) phytoavailability was investigated in a pot trial with two contrasting soils (Kereone (Allophanic), total Cd 0.79 mg kg⁻¹; and Topehaehae (Gley), total Cd 0.61 mg kg⁻¹) that were either sown with plantain (Plantago lanceolata) or left unseeded. Varying soil moisture contents were established using contrasting irrigation regimes: “flooded” (3 days flooded and then 11 days drained); or “non-flooded” (irrigation to 70% of potted field capacity every 7 days). Overall, there was no significant difference in mean 0.05 M CaCl₂ soil extractable Cd concentrations or plant tissue Cd concentrations between flooded and non-flooded irrigation. However, there was a consistent trend for an increase in soil extractable Cd concentrations following irrigation, regardless of the irrigation regime. Mean soil extractable Cd and plant tissue Cd concentrations were significantly greater (approximately 325% and 183%, respectively) for the Topehaehae soil than the Kereone soil, despite the lower soil total Cd concentration of the Topehaehae soil. These results indicate that Cd solubility is sensitive to increases in soil moisture following periods of soil drainage, but insensitive to short-term periods of soil saturation. Plant tissue Cd concentrations in Cd-sensitive forage crops such as plantain are likely to be greater following large rainfall events over summer and autumn. This has the potential to increase animal dietary Cd exposure and rate of liver/kidney Cd accumulation. Full article