Sand Fractions Of Soils Research Articles

Serpentine Soil Redness, Differences among Peridotite and Serpentinite Materials, Klamath Mountains, California

Peridotite soils were perceived to be redder than serpentinite soils. These redness differences were confirmed by relating soil redness to bedrock specific gravities and to heavy mineral concentrations in fine sand fractions of soils. The redness differences are explained by mineralogical differences between peridotite and serpentinite. Soil redness in well-drained soils of the Klamath Mountains is closely related to free iron in oxides and oxyhydroxides. Most of the iron in peridotite is in olivine, which is readily weathered to release iron that is then oxidized in well-drained soils, whereas most of the iron in serpentinite is in magnetite and serpentine. Magnetite is very resistant to weathering and serpentine weathers more slowly than olivine and pyroxene. This relationship predicts untested redness differences in soils derived from serpentinized dunite (redder soils) compared to those from more silicic serpentinized peridotite such as lherzolite.

Mineralogia e formas de potássio e magnésio em diferentes classes de pesos e tamanhos da fração areia de solos do Triângulo Mineiro

O presente trabalho objetivou estudar a distribuição da reserva de K e Mg nas diferentes classes da fração areia de solos do Triângulo Mineiro, destacando-se o potencial de liberação de formas não-trocáveis e estruturais destes nutrientes para as plantas. A seleção do local de amostragem foi definida com base nas diferenças entre os materiais de origem (Grupo Bauru, Araxá, São Bento e Coberturas Detrítico-Lateríticas Terciárias), estádio de desenvolvimento dos solos e representação espacial das litologias. Amostras da fração areia dos solos foram separadas em areia leve (AL) e pesada (AP) com uso do bromofórmio (densidade 2,8 g cm-3) e, por meio de um conjunto de peneiras, a fração AL foi separada em cinco classes diferentes: areia muito grossa (AMG), areia grossa (AG), areia média (AM), areia fina (AF) e areia muito fina (AMF). Os teores totais e não-trocáveis de K e Mg foram obtidos após digestão das amostras com HF, HNO3 e H2SO4 concentrados e com HNO3 1 mol L-1 fervente, respectivamente. Na caracterização mineralógica da fração areia, utilizou-se a difração de raios-X. A fração areia dos solos é composta basicamente por quartzo, com predomínio de minerais leves e de menor tamanho (AF e AMF). Em geral, os difratogramas de raios-X da fração areia apresentaram apenas reflexões discretas de minerais primários fontes de nutrientes (MPFN), como mica e feldspato. Dentro da AL, os maiores teores de K e Mg totais foram advindos das frações mais finas (AF e AMF), tendo a fração AM apresentado a menor liberação de formas não-trocáveis destes nutrientes. Observou-se que solos com teores totais elevados de K e Mg na fração areia, geralmente, apresentaram maior capacidade de liberação de parte desses nutrientes para a solução do solo, atribuída à maior presença de MPFN. A fração areia dos solos originados de arenito da Formação Uberaba e de migmatito/micaxisto do Grupo Araxá apresentaram as maiores reservas e liberação de K e Mg.

Impact of irrigation scheduling practices on pesticide leaching at a regional level

Information about how current and proposed management practices impact environmental quality is required to develop best management practices. A modeling approach was used to evaluate the scheduling practices of local farmers and two other irrigation scheduling practices for their potential impact on groundwater pollution in Doña Ana County, New Mexico. Data about farmers’ practices came from historical information about the timing and quantity of water delivered to the farms. The irrigation scheduling practices were: tensiometer-based with the tensiometers placed at 50% or 75% of the root-zone depth and irrigations started when tensiometer’s readings reached 6 kPa for sandy soils, 23 kPa for sandy loam soils, 44 kPa for loamy soils, and 74 kPa for clay loam soils; and at 50% plant available water depletion (PAWD) level regardless of soil type. The objective was to use irrigation scheduling model ( IRRSCHM), a volume balance, mixing-cell, type irrigation scheduling and pesticide transport model, to assess and compare the impact of different irrigation scheduling practices on cyanazine (Bladex) and metolachlor (Dual) concentrations at 180 cm below the soil surface during a 30-year cropping sequence. The region was divided into different soil textural classes to facilitate rapid estimation of soil parameters needed for the model. Very low Bladex and Dual concentrations were predicted at 180 cm below the soil surface. However, the predicted pesticide concentrations increased as soil sand fractions increased, regardless of the irrigation scheduling practice. The tensiometer based irrigation scheduling resulted in the highest Bladex and Dual concentrations. The lowest concentrations were predicted under the farmer’s practices due to deficit irrigation. Dual concentrations at 180 cm depth of the sandy soil class were about 20 times less than the 5.25 × 10 −1 mg l −1 Health Advisory Level under the tensiometer-based irrigation scheduling practices, while, the farmer’s practices resulted in Dual concentration about 625 times less than the Health Advisory Level. Similarly, the predicted Bladex concentration in sandy soil class was 3125 times less than the 1.30 × 10 −2 mg l −1 Bladex Health Advisory Level under the tensiometer-based irrigation scheduling and about 416 000 times less than the Health Advisory Level under farmer’s practices. Simulation results suggested that current farmer’s practices do not pose a threat to the area’s groundwater quality and result in a 15–40% leaching fraction depending on soil type. Tensiometer-based irrigation scheduling was similar to scheduling irrigations at 50% plant available water depletion and resulted in a 35–50% leaching fraction depending on soil type as long as the tensiometer was placed in the proper root zone depth. The model’s calculated leaching fractions using farmer’s practices were similar to measured leaching fractions in Doña Ana County, giving credibility to the use of simulation models for assessing and comparing the potential impact of different irrigation scheduling practices on environmental quality at a regional level.

Organic C and N storage, and organic C fractions, in adjacent cultivated and forested soils of eastern Canada

As a major attribute of soil quality, organic matter is responsive to agricultural land use practices including tillage. A study was initiated in eastern Canada to characterize changes in the masses of organic C and total N, and organic matter fractions in forested and adjacent cultivated or forage sites. Generally, the cultivated and forage sites had denser soil profiles than the forest sites. Based on an equivalent soil mass, to accommodate differences in soil bulk density, the paired forest and cultivated sites showed that cultivation decreased the mass of organic C (35%) and total N (10%) in the soil profile of the Podzolic soils, but increased organic C (25%) and total N (37%) in the Brunisolic (Cambisol) and Gleysolic soils. For the Podzolic soils, use of forages increased soil stored organic C and N by 55% and 35%, respectively. Organic C fractions were mainly of significance in the A horizon. Soil microbial biomass C was greater in the forested, compared to the cultivated soil, but the proportion of soil organic C as microbial biomass C (1.3% to 1.6%) was similar. The proportion, however, was greater (2.1%) for the forage soil, compared to the corresponding cultivated (1.3%) soil, suggesting that organic C was continuing to increase under the former. The relatively large proportion (19%) of organic C found in the light fraction of forest soils in the A horizon was decreased (up to 70%) by cultivation. In contrast, the proportion of macro-organic C present in the soil sand fraction was not greatly influenced by cultivation. Overall, soils in eastern Canada have a relatively large potential to store organic matter. The study illustrates the importance of soil type and cultivation interactions for maintenance of soil organic matter storage, and the positive influence of forages in this regard in agroecosystems.

A search for the origin of cadmium in the soil of the Swiss Jura

The top soil of a 14.5 km2 region at la Chaux-de-Fonds in the Swiss Jura is exceptionally rich in cadmium. It contains an average of 1.3 mg per kg of soil. The spatial distribution of the metal has no simple pattern that could be explained by atmospheric deposition or agricultural practices.Thin soil contained most of its Cd at the surface; in thicker soil Cd is mainly concentrated between 60 and 80 cm depth. No specific minerals or soil fractions could account for these accumulation, and the vertical distribution of Cd is best explained by leaching from the topsoil and further adsorption within layers of nearly neutral pH.The local Jurassic sedimentary rocks contained too little Cd to account for the Cd concentrations in the soil. Alpine gravels from glacial till were too sparse in soils to explain such a spreading of Cd. Moreover this origin is contradictory with the fact that Cd is concentrated in the sand fraction of soils. The respective distributions of Fe and Cd in soils, and soil fractions, suggested that the spreading of iron nodules accumulated during the siderolithic period (Eocene) was not the main source of Cd. Atmospheric deposition, and spreading of fertiliser or waste from septic tanks seem the only plausible explanation for the Cd concentrations, but at present few factors allow us to differentiate between them.

The nature of weathered biotite in sand-sized fractions of Gray Luvisols (Boralfs) in Saskatchewan, Canada

The nature of weathered biotite in sand-sized fractions in two Gray Luvisols developed from Wisconsinan-age glacial till under Boreal Forest in east central Saskatchewan was studied. Weathered biotite was quantitatively isolated using a new liquid magnetic separation technique, from sand fractions of soils without any chemical pretreatments. Most of the grains in sands (100–2000 μm) were associated with low specific gravity (< 2.70) fractions. The heavy fraction (> 2.95) did not contain any weathered or unweathered biotite. The low content of weathered biotite in the surface horizons was attributed to physical breakdown of sand particles. The grains in the solum horizons were heavily coated with sesquioxides and were light brown to shiny golden as compared to those from the C horizons. Optical and scanning electron microscopic studies showed a high degree of splitting and opening of layers in all the samples due to intensive layer weathering and exfoliation, curling, and folding of layers, especially in the solum, due to edge weathering. Observed crystal defects, mineral inclusion holes and deep cracks further promoted the edge and layer weathering of the grains. Wet chemical and X-ray micro-analyses revealed very low K 2O (5% in the surface and 2.4–3.3% in the subsurface horizons) and high water contents of weathered biotite grains. X-ray diffraction results show that almost all the grains have weathered to vermiculite and mixed-layer minerals of biotite-vermiculite nature. Re-potassification of vermiculite in the surface horizons is believed to be pedogenic. Biocycling through the decomposing organic matter is likely the source of potassium causing transformation of vermiculite to biotite. This study also suggests that the weathered biotite in glacial till, being low in potassium content, can fix potassium.

LIQUID MAGNETIC SEPARATION OF IRON-BEARING MINERALS FROM SAND FRACTIONS OF SOILS

The study provides a new liquid magnetic separation (LMS) technique for concentrating sand-sized iron-bearing minerals, in general, and for quantitative isolation of biotite, in particular, from soils. Sand fractions (100–250 μm), separated from untreated soil samples from a Gray Luvisol from Saskatchewan by ultrasonic dispersion and sieving, were processed by LMS at various levels of magnetic flux density. The LMS separates obtained at increasing level of magnetic flux density showed a decreasing iron content. A linear relationship was observed between the two variables within the range of 2.5–28.0% Fe2O3 and 0.15–0.92 Tesla (T) magnetic flux density with a correlation value of R = 0.99. Mineral grains with as low as 1.09% Fe2O3 content could be isolated from sand fractions at 1.31–1.45 T. The XRD analyses of LMS separates obtained at 0.305–0.58 T showed only biotite and its weathered products. The XRD analyses of other LMS separates showed a concentration of different solid solution series of the amphiboles, pyroxenes, garnets, tourmaline and other iron-bearing minerals in different fractions. The LMS technique is physical in nature and provides a simple, quick and effective means of isolating iron-bearing minerals from sand fractions of soils. Key words: Liquid magnetic separation, iron bearing minerals, biotite separation, sand mineralogy

Origin of quartz in selected soils and sediments, North Island, New Zealand

Abstract Quartz from two marine shales has δ18O values indicative of low-temperature crystallisation. In a Mangakahia Group shale, the lowtemperature quartz is confined to the silt fraction and is a result of diagenesis; in the Whangai Shale, it occurs as clastic chert in a range of grain sizes. Quartz in soils formed from andesitic and basaltic parent materials is of eolian rather than pedogenic origin. However, quartz in the sand fractions of soils formed from a range of parent materials, including volcanic, has a δI8O value indicative of high-temperature formation and was probably a component of rhyolitic tephras from central North Island. Similar δ18O values for quartz in beach sands from the west coast of Northland indicate a predominantly rhyolitic source, and higher δ18O values of quartz in east coast beach sands indicates the presence of additional locally derived sediment. Only one example of low-temperature quartz was found in the soils investigated but this was found to be of eolian origin. Qua...

Estimation of Components of Soil Cation Exchange Capacity from Measurements of Specific Surface and Organic Matter

AbstractCation exchange capacities of Irish soils developed from a wide range of parent materials were found to be highly correlated with organic matter content and specific surface but not with clay content. Multiple regression analysis showed that organic matter in combination with specific surface accounted for 97% of the variation in CEC whereas organic matter and clay content only accounted for 58% of the variation. The better correlation between CEC and specific surface than between CEC and clay content, is attributed to the ability of surface area measurements to reflect the presence of phyllosilicates in silt and sand fractions of soils and to the fact that these minerals have less variable surface charge densities than cation exchange capacities. It is proposed that specific surface provides a better estimate than clay content, of the mineral component of CEC for soils of varying mineralogy.

Availability of Residual Phosphorus from Long‐Time Rock Phosphate and Superphosphate Applications to Groseclose Silt Loam

AbstractThe availability of residual phosphorus from long‐time superphosphate applications to Groseclose silt loam exceeded that of rock phosphate. Based on A values, residual phosphorus from superphosphate was approximately four times as available as that from rock phosphate.Data on total, Truog, and NaHCO3‐soluble phosphorus showed that: (1) more of the superphosphate had reacted with the soil than had rock phosphate; (2) more of the phosphorus applied as superphosphate had accumulated in the silt and clay factions of the soil and, based on solubility in NaHCO3, was relatively available; and (3) more of the phosphorus applied as rock phosphate had accumulated in the sand fraction of the soil and was relatively unavailable, as judged by solubility in NaHCO3.Apparently, some of the rock phosphate had not reacted with the soil and was still in its original molecular combination. X‐ray analysis revealed the presence of apatite or a mineral similar to apatite in the sand fraction of soil that had received rock phosphate. The mineral, which gave pronounced reflections at the same values obtained from rock phosphate fertilizer, was not found in soil receiving superphosphate.Approximately three‐quarters of the phosphorus applied over a 40‐year period from either source was present in the soil as residual phosphorus. This quantity nearly doubled the total phosphorus content of the soil. Crop yields on plots receiving the two fertilizers have been equal except for the first few years when superphosphate produced higher yields.

Size distribution in the sand fractions of soils

Size distribution in the sand fractions of soils