Soil Mineralogy Research Articles

Assessing soil mineralogy and weathering degree by a multi-range sensor synergistic approach: From parent rock to topsoil

The weathering degree (WD) of soils is usually based on the presence of weatherable primary minerals and the content of chemical elements along the soil profile, which traditionally demand expensive, time-consuming and environmentally unfriendly laboratory analyses (e.g. wet chemistry). To address this issue, proximal sensors often operating in only a single spectral range have been used in soil WD assessments. In this sense, we analyzed in detail the performance of proximal sensors operating at several spectral ranges to assess the soil mineralogy and WD. We selected three soil profiles developed from sedimentary rocks and analyzed samples from parent rock to topsoil. Samples from each horizon of the soil profiles and from the parent rock were collected and submitted to chemical, physical and mineralogical laboratory analyses. These samples were also analyzed using several sensors operating within different spectral ranges, i.e., gamma-ray, X-ray fluorescence (XRF), visible (VIS), infrared (IR) (near infrared, NIR, shortwave infrared, SWIR, and middle infrared, Mid-IR), and the AISA Fenix hyperspectral imaging systems (VIS-NIR-SWIR). Several WD indices were calculated using laboratory (reference) and multi-range sensor data for comparison. The spectral differences in the VIS-IR range were evaluated according to the soil mineralogy and WD. Gamma-ray and XRF sensors presented high correlation with the main soil elements in oxide minerals used in the WD quantification (R ranging from 0.70 to 0.99). We detected differences associated with the WD of each horizon of all profiles using data from VIS to Mid-IR ranges. The application of linear models to AISA images enabled the mapping and quantification of main elements along one soil profile (R2 ranging from 0.48 to 0.8) using a pixel-to-pixel approach, which facilitated the interpretation of the WD. Due to the specificity of each spectral region, the use of several sensors at different wavelengths provided a holistic overview of mineralogy and WD of the analyzed soil profiles, using a quick and non-destructive approach. This technique produces overlapping and/or complementary information of WD and mineralogy from all spectral ranges and can significantly assist traditional laboratory methods.

Mineral composition and its relations to readily available element concentrations in cultivated soils of Finland

ABSTRACT Mineral composition is a fundamental feature that affects the properties and functions of soil through physical, chemical and biological interactions. However, comprehensive knowledge on the mineralogy of agricultural topsoils of Finland has been lacking. In this study, the mineral composition of 120 soil samples included in the national monitoring of agricultural soils of Finland was determined using state-of-the-art quantitative x-ray diffraction analysis by a prior measured full pattern fitting methodology. Quartz, plagioclase and K-feldspar were found to be the dominant soil mineral components. Amphiboles and micas were also common, and several other mineral phases were detected in small quantities. The relative proportions of quartz and plagioclases increased and those of mica, goethite, disordered clay minerals, kaolin and amorphous inorganic components decreased as the soil particle size increased. Compositional statistical analysis discerned a positive association between the prevalence of 12 elements and organic matter and surface-active minerals (goethite, chlorite, disordered clays, kaolin and inorganic amorphous materials), whereas micas contributed to the prevalence of K. The present data agreed with general conceptions of Finnish soil mineralogy but revealed novel details in the mineral composition. The relationship observed between soil textural and mineral compositions supports the current texture-based soil classification system and recommendations.

Influence of chemical and mineralogical soil properties on the adsorption of sulfamethoxazole and diclofenac in Mediterranean soils

BackgroundThe irrigation with treated wastewaters can be a way for the introduction of organic contaminants in soils. However, their adsorption onto soils can allow a control of their bioavailability and leaching. The adsorption is influenced by properties of contaminants (water solubility, chemical structure) and soils (organic matter content, pH, mineralogy). This study aimed to investigate the effect of mineralogical composition, organic matter content and others parameters of soils on the adsorption of sulfamethoxazole (SMX) and diclofenac (DCF), two contaminants of emerging concerns (CECs), in real cases (Altamura, Sibari and Noci soils).ResultsThe isotherms data showed that the adsorption of the two CECs closely matched the Freundlich model, even if the DCF could also fit the linear one. The only exception was the adsorption of SMX on the soil of Sibari, for which Langmuir's model fitted better. In all cases, the Kd values were the highest for Altamura soil according mainly to its content of organic carbon. Positive correlations were found between Kd value of DCF and the soil organic carbon and Al oxyhydroxides content, suggesting their roles in its adsorption, while SMX showed only a slight positive correlation with the soil organic carbon content. Finally, between the two CECs studied, DCF was more adsorbed than SMX also because of the lower water solubility of the former.ConclusionsThe good interaction between DCF and soil organic carbon suggests the organic amendment of soils before the application of treated watewaters. The low adsorption of SMX onto soils suggests greater leaching of this compound which is, therefore, potentially more dangerous than DCF. For this reason, the application of a filtration system with appropriate adsorbent materials before the application of wastewater to soils should be expected.Graphical

The Pedogenesis of Inceptisols on Southeast Toposequence of Mount Manglayang in West Java, Indonesia

DOI:10.17014/ijog.9.2.195-208The most potential soil order in Indonesia is dominated by Inceptisols, whereas the topography combined with a climatic factor are the main factors to regulate pedogenetic process. This research was intended to determine the pedogenetic process and soil development on various terrain positions at the southeast toposequence of Mount Manglayang areas that have hilly topography. The researched area was 28.83 ha. Based on those conditions, this research aims to study the pedogenetic process and soil development in the southeast slope toposequence of Mount Manglayang, the relationship between the physical, chemical, and mineralogical soil properties, the soil classification to family level based on soil taxonomy, National Soil Classification, and FAO soil classification systems. This research used survey, descriptive, and comparative methods. The result showed that the pedogenetic processes identified were the formation of B horizon through clay accumulation, soil colour, and soil structure development, and the formation of amorphous kaolinite and halloysite minerals. Based on soil taxonomy, the soil were classified as Fluventic Humudepts, coarse-loamy, kaolinitic, isohyperthermic at the upper slope and Fluventic Dystrudepts, fineloamy, kaolinitic, isohyperthermic at the middle and lower slopes. According to National Soil Classification, the soil is Humic Cambisol at the upper slope, Distric Cambisol at the middle slope, and Cromic Cambisol at the lower slope. FAO classified the soil as Umbric Cambisols at the upper slope and Dystric Cambisols at the middle and lower slopes.

The mechanistic investigation of geochemical fractionation, bioavailability and release kinetic of heavy metals in contaminated soil of a typical copper-smelter

Identifying the bioavailability and release-desorption mechanism of heavy metals (HMs) in soil is critical to understand the release risk of HMs. Simultaneously, the mechanistic investigation of affecting the bioavailability of HMs in soil is necessary, such as the grain-size distribution and soil mineralogy. Herein, the bioavailability of HMs (Cu, Cd, Ni, Pb, and Zn) in different area soils near a typical copper-smelter was evaluated by the sequential extraction technique (BCR), diffusive gradients in thin-films (DGT), and DGT-induced fluxes in sediments (DIFS) model. Results showed that the HMs proportion of the residual fraction in all soils was the highest. The average bioavailability concentration (CDGT) of Cu and Cd in industrial soil was the highest, with 45.12 μg· L−1 and 9.06 μg· L−1. The result of DIFS model revealed that the decreased order of the mean value of desorption rate constant (K-1) was Cd > Zn > Ni > Cu > Pb, 5.91 × 10−5, 4.96 × 10−5, 2.89 × 10−5, 9.64 × 10−6, and 8.69 × 10−6, respectively. According to the spatial distribution of release potential (R-value), the release potential of labile-Cu in agricultural soil was the highest, which was mainly attributed to fertilizer application in farmland. Simultaneously, the reduced hydroxyl was also related to the agricultural activities, resulting in the weakened adsorption capacity of HMs by soil. Redundancy analysis (RDA) results showed that the bioavailability of Cd, Ni, and Zn was mainly driven by soil pH, while the bioavailability of Cu and Pb was primarily driven by dissolved organic carbon (DOC). Meanwhile, carbonate minerals had a positive correlation with the bioavailability of Cd, Ni, and Zn, which could promote the release of HMs in mining soil as chemical weathering progresses. In conclusion, this study provides a structured method which can be used as a standard approach for similar scenarios to determine the geochemical fractionation, bioavailability, and release kinetics of heavy metals in soils.

Changes in inorganic phosphorus fractions in weathered soils under long-term intensive cultivation and irrigation

ABSTRACT Conventional intensive cultivation tends to modify the interactions of phosphorus in soil, favoring inorganic forms transformations. The aim of the study was to evaluate the status of inorganic phosphorus and correlate with the chemical, physical and mineralogical soil properties in areas under natural vegetation and different cultivation periods: 1, 17, 22, 28, 32 and 43 years. Soil P was extracted using Chang and Jackson method (Al-P, Fe-P, Ca-P and Residual-P). The micro-chemical map of P concentrations within the representative aggregates was determined by electron probe. Results showed that biofertilizers application in the area under intensive cultivation for 32 years of use significantly increased all soil P fractions (4.249 mg kg−1 in upper soil layer). There was a slight increase in the P at the edges of the aggregates in the first year (0.23%), but at 43 years, there was an increase in contents within the aggregates (0.32%). The intensive cultivation promoted the increase of P content in soil fractions in the arable layer of the soil over time. However, the decline in inorganic P contents after a few years of cultivation suggests that the soils of the studied areas tend to exceed their maximum adsorption capacities in the future.

Magnetic phases of soils developed from igneous rocks in a climate gradient transept, Brazilian northern Amazonia

Knowledge on magnetic phases and properties of magnetic minerals has wide applications in soils and in agriculture, by the possibility, and perspectives in application of rock magnetic methods in soil science and agriculture; however, their role in highly weathered soils is still unclear. We characterized the mineralogy of soils from Brazilian northern Amazonia, with emphasis on magnetic soils. Samples with varying weathering degrees were collected from four different localities, and their magnetic phases (MPs) were separated and subjected to the following analysis: X-ray fluorescence (XRF), X-ray diffractometry (XRD), and measurements of field and temperature magnetization. The chemical composition by XRF analyses revealed the predominance of Fe, Si, Ti, and Mn. The XRD analysis, using the Rietveld method, revealed the presence of hematite, goethite, maghemite, and magnetite as magnetic phases: The highest concentration of MPs was detected in an Fe-rich Typic Eutrudept (54% magnetite). Magnetization measurements of the magnetic phases showed the presence of magnetite, associated with hematite and goethite, with magnetization values and transition temperature characteristics of these minerals. The magnetization varied according to soil type, indicating different weathering processes. Soil magnetism varied as a function of parent igneous rocks, in the following order: diabase > basalt > granite. The results indicate that parent material and mineral weathering influence soil magnetism in a tropical climate.

Comparative effectiveness of fibers in enhancing engineering properties of Earth as a building Material: A review

Earth is becoming increasingly popular as a building material to promote sustainability, considering environmental impacts and economic aspects. Recent studies have focused on enhancing the engineering properties of earth and earthen construction using different types of fibers, which is considered one of the suitable options for soil reinforcement. A comprehensive review considering the effectiveness of different fibers, their dosages, and their relationship with various engineering properties of stabilized earth is missing in the literature. Therefore, this study aims at providing a state-of-the-art review of research on the effectiveness of fiber reinforcement techniques in overcoming the limitations of the earth and enhancing the engineering characteristics of the reinforced earth. Based on 96 existing studies, the properties and types of fiber and soil, sample-making processes, and engineering properties of fiber reinforced earth, including physical, thermal, mechanical, and durability properties, are reviewed and presented in recapitulative tables. The review demonstrates that there is no specific fiber that showed the best performance considering all the properties; rather, different fibers proved to be best at improving different properties. The present study should aid in the selection of superior fibers and their suitable contents depending on the required engineering properties of earth for being used in construction. Furthermore, this study provided directions for future studies, which should focus on soil mineralogy, the effectiveness of combinations of different fibers, microstructural analysis, and the development of a widely accepted code to promote earthen construction.

Reclamation of post-tin mining areas using forages: A strategy based on soil mineralogy, chemical properties and particle size of the refused materials

The physical and chemical properties of refused materials in post-mining areas have received in-depth attention, while the mineralogy as a driver of the potential nutrient reserve has been ignored in reclamation practices. The objective of the study was to evaluate mineralogical, chemical, and physical properties and heavy metals of refused materials (spoil and tailings) as the basis for reclamation. Seven representative soil profiles were described and sampled to a depth of 130 cm for various soil analyses and to assess soil limiting factors for crop growth. Eleven forage species were tested in a field plot trial and their adaptability and biomass production against extreme limiting soil properties were evaluated for two consecutive growing seasons. Results showed that tin mining has drastically altered the soil texture from sandy clay loam under native conditions to loamy sand and sand under post-tin mining, resulting in serious unfavourable conditions for crop growth. Potential nutrient reserves have been depleted as revealed by the dominance of quartz minerals with small amounts of tourmaline, opaque minerals, zircon and garnet. Total elemental analysis using X-ray fluorescence (XRF) showed extreme high SiO2 content (92–96%) associated mainly with the dominance of quartz in the mineral constituents, and extremely low contents of Ca, Mg, P, K and S expressed as oxides (<0.2% altogether). This suggests that all nutrients are a severe constraint for crop growth. Among the analyzed total heavy metals, Cr2O3 contents were high (204–286 mg kg−1), while SnO contents were low (0–153 mg kg−1). However, the health risk is negligible because they were preserved in the structure of host minerals. Rehabilitation of post-tin mining was successfully performed using various forage types by implementing “a pot planting point system” accompanied by animal manure and complete fertilizer applications. Six out of the eleven forages tested, namely Cynodon dactylon, Pennisetum purpureum cv Mott, Brachiaria decumbens cv Humidicola, Pennisetum purpureum cv Taiwan, Brachiaria decumbens cv Mulato, and Paspalum atratum were recommended based on their high adaptability and significantly higher fresh biomass production (varying from 16.5 to 24.7 ton ha−1 season-1). Findings from this study provide alternatives for forage production systems to support livestock establishment. Soil mineralogy provides important information on nutrient reserves and should be considered part of an integral soil characterization including physical and chemical properties, and heavy metal contents of post-tin mining sites to ensure successful reclamation.

Soil geochemistry as a driver of soil organic matter composition: insights from a soil chronosequence

Abstract. A central question in carbon research is how stabilization mechanisms in soil change over time with soil development and how this is reflected in qualitative changes in soil organic matter (SOM). To address this matter, we assessed the influence of soil geochemistry on bulk SOM composition along a soil chronosequence in California, USA, spanning 3 million years. This was done by combining data on soil mineralogy and texture from previous studies with additional measurements on total carbon (C), stable isotope values (δ13C and δ15N), and spectral information derived from diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). To assess qualitative shifts in bulk SOM, we analysed the peak areas of simple plant-derived (S-POM), complex plant-derived (C-POM), and predominantly microbial-derived organic matter (OM; MOM) and their changes in abundance across soils with several millennia to millions of years of weathering and soil development. We observed that SOM became increasingly stabilized and microbial-derived (lower C : N ratio, increasing δ13C and δ15N) as soil weathering progressed. Peak areas of S-POM (i.e. aliphatic root exudates) did not change over time, while peak areas of C-POM (lignin) and MOM (components of microbial cell walls (amides, quinones, and ketones)) increased over time and depth and were closely related to clay content and pedogenic iron oxides. Hence, our study suggests that with progressing soil development, SOM composition co-varied with changes in the mineral matrix. Our study indicates that structurally more complex OM compounds (C-POM, MOM) play an increasingly important role in soil carbon stabilization mechanisms as the mineral soil matrix becomes increasingly weathered.

Saprolithology applied to pedology: Mineral alteration in soil-saprolite profiles along a climate gradient in Triunfo Massif (NE Brazil)

Saprolites, along with bedrock, are the main parent materials of soils worldwide. In Northeast Brazil, the climate-geomorphology relationship in specific regions, called “humid islands”, affects saprolite weathering. This regional peculiarity generates a climatic gradient that influences the weathering of crystalline rocks and the genesis of soil-saprolite systems representative of other regoliths found on a global scale. In this study, we combined saprolithology and pedology (soil mineralogy and soil geochemistry) to better understand the weathering process of soil-saprolite profiles derived from syenite along the Triunfo Massif – NE Brazil. We collected soil and saprolite samples to determine the primary and secondary mineralogical assemblies and describe possible pathways of alteration for these minerals using X-ray diffractometry, optical microscopy, and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. We also determined the weathering degrees of soil horizons and saprolite layers based on mineralogical (Xd and Ip) and chemical indexes (chemical index of alteration, chemical index of weathering, and plagioclase index of alteration). The results showed that the climatic gradient influenced the weathering of minerals, such as K-feldspars, plagioclases, biotite, and hornblende and the pathways of alteration of these primary minerals. We also found that the types of secondary minerals formed are rather similar. The wetter climate at the Massif summit resulted in higher weathering index values and favored pathways of alteration associated to the formation of iron oxides and 1:1 secondary phyllosilicates. The drier climate at the Massif base favored other pathways of alteration associated to the formation of 2:1 secondary phyllosilicates. In addition, micromorphological and geochemical evidence demonstrated an inversion in the classical sequence of mineral stability and biotite was more altered than hornblende placed side by side, possibly due to the influence of structural and geochemical factors.

The impact of environmental factors on early stage Andosol development south of Vatnajökull, Iceland

AbstractIcelandic soils develop in a dynamic environment affected by both natural processes and anthropogenic impacts. We present an extensive investigation of soil mineralogy and pedogenesis in a disturbed (i.e., by solifluction) pedon under such conditions. The study focuses on two distinct tephra layers, a rhyolitic tephra from the Öræfajökull eruption in 1362 CE (Ö1362) and a basaltic Veiðivötn tephra from 1477 CE (V1477). Both tephra layers form an important parent material in the study area south of Vatnajökull, Iceland. The Andosol developed from tephra and aeolian material, rich in volcanic glass. The pH (H2O) values were between 5.5 and 6.6 and clay mineralogy displayed a predominance of allophanic material in both soil and tephra. The pedon can be seen in its early stage of chemical weathering and soil development. Despite the overall predominance of non‐ and poorly‐crystalline short‐range order secondary materials and Fe (hydr)oxides in the clay‐size fraction, we found indication of smectite. High exchangeable Ca2+ and Mg2+ concentrations reflect enhanced aeolian input of volcanic material, while elevated exchangeable‐Na+ concentrations are most likely caused by the oceanic composition of precipitation. The impact of erosion and aeolian processes on pedogenesis seemed to be higher between the deposition of Ö1362 and V1477, than in the soils above. Both, soil and tephra layers appeared disturbed by erosion–deposition processes over time. Characterised by a significantly coarser particle size composition, low soil organic carbon (SOC) content, and a more diverse mineralogy, a distinct fluvial sediment layer at 10–30 cm depth appeared sharply contrasting to the other soil layers in the profile. This possibly reflects the diverse composition of glaciofluvial material from a landslide originating from a Kvíárjökull moraine in the north. Changed weathering patterns and properties in the soils above the Ö1362 tephra indicated soil degradation following the deposition of the rhyolitic tephra.

Microbial formation and stabilisation of soil organic carbon is regulated by carbon substrate identity and mineral composition

The view that soil organic C (SOC) is formed mainly from non-metabolised and recalcitrant organic residues is being challenged by an emerging view that metabolic by-products form more stable associations with soil minerals. However, the effects of C substrate identity and soil mineral composition (and interactions) on microbial physiology and SOC formation are still not well understood. We added contrasting substrates (glucose, alanine and a mixture of glucose, alanine, and oxalic acid) into artificial soils of varying mineral composition (montmorillonite, kaolinite, and kaolinite plus goethite and hematite) for 12 weeks. We found that glucose led to 1.45 and 1.75 times more SOC formation than alanine and the mixed substrate, respectively. Montmorillonite-based soils gained approximately 1.3 times more SOC compared to the other two soils. Compared with kaolinite-only soils, the inclusion of goethite and hematite had a positive effect on total SOC, extracellular C and biologically stable C when amended with alanine, but a negative effect on these SOC fractions when amended with glucose. Soils with greater SOC formation were associated with high microbial C use efficiency (CUE) and extracellular C, suggesting that spatial allocation by the microbial biomass is pivotal for creating stable SOC. Fungi-dominated soils typically had a higher CUE, which was positively correlated with the formation of new SOC. These results suggest that the identity of plant inputs will have a strong bearing on the formation of SOC via interactions with the soil microbial community and soil mineralogy.

Porous frameworks from Ecuadorian clays

This research provides a literature review on several topics as a foundation to comprehend porous materials, their structure, and behavior to explore how they can be derived from clays and nanoclays. In this case, considering the several minerals present in some Ecuadorian clays, which are a potential starting material for the synthesis of porous frameworks, they constitute a solid source of metal atoms such as Silicon or Aluminum. This research presents the evaluation and characterization via XRD and AAS of clay samples collected in the southeast of Ecuador in the provinces of Azuay, Morona Santiago and Zamora Chinchipe, which present diversified soil mineralogy with many chemical and crystallographic features for suitable precursors in nanomaterials design.

Effect of Temperature on Local Hydration of Zn in Hematite

Iron (oxyhydr)oxides are common soil minerals that can be host phases to a large number of environmentally important elements, such as the micronutrient Zn. The structure and hydration level of these host phases change significantly if the soil is heated, as is the case during wildfires, for example. Steady increases in the frequency and scale of wildfires in recent decades thus raises the question of whether these events significantly impact the geochemical availability of trace elements incorporated within the reacting iron (oxyhydr)oxides. In this contribution, we focus on Zn-substitution into two abundant iron minerals in soil, hematite (α-Fe2O3) and goethite (α-FeOOH). Using ab initio molecular dynamics (AIMD)-informed extended X-ray absorption fine structure (EXAFS) spectra, we determine the local environment of Zn in hydrothermally precipitated material and after annealing at 500 and 800 °C. Results show that Zn was incorporated into the hematite structure by preferential formation of coupled O–Fe and protonated Fe vacancies (PFe). These defects increase in density around Zn upon heating the samples to 500 °C, particularly PFe. Heating to higher temperatures produced franklinite (ZnFe2O4), a highly refractory zinc iron spinel. This difference in structure and hydration of Zn sites suggests soil mineralogy and wildfire temperature impact the local coordination of trace elements, which may play a role in controlling the bioavailability of these elements.

Investigating physical and mechanical properties of nest soils used by mud dauber wasps from a geotechnical engineering perspective

The quality of nest soils has significant effects on reproductive success in mud dauber species. This study investigated the physical and mechanical properties of the nest soils used by mud daubers from a geotechnical engineering perspective. One hundred thirty-one nests of black and yellow mud daubers were collected from five locations in the south of Louisiana. Moisture and organic contents, densities, void ratios, plasticity, grain size distributions, soil classifications, and penetration resistances of the nest soils were measured. Also, the performance of mud daubers’ nest-compaction method (i.e., repetitive tapping produced by the front legs and mandibles) was evaluated by comparing the densities and penetration resistances between mud dauber nests and Proctor compacted nest soil samples. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction were used to measure the morphology, elemental composition, and mineralogy of the nest soils. Mud dauber nests were made of hard and very stiff well-graded silty soils. The high strengths and high densities of mud dauber nests were attributed to repetitive tapping (similar to vibratory compaction in geotechnical engineering) used by mud daubers for nest construction, high capillary cohesion in the nest soils, well-graded soil grain size distribution, and clay minerals serving as cementing agents in the nest soils.

Proposed changes to the soil family taxon within the Canadian System of Soil Classification

The soil family was developed in the 1960s as the fourth level of taxa within the hierarchical structure of the Canadian System of Soil Classification. The original aim of the soil family category was to provide a framework for checking and establishing limits for soil series while providing a link between the series and the subgroup level. Its intended use was to define and group numerous soil series based on soil characteristics important for the purpose of applying appropriate management practices. In the current Canadian System of Soil Classification, taxa at the family level represent subdivisions of the subgroups. Classification of mineral soils at the family level is based on properties of the parent materials which include particle size; soil mineralogy; reaction (soil pH); calcareousness; depth to bedrock and permafrost; as well as climactic factors: soil temperature and soil moisture regimes. The soil family particle-size classes were originally intended as a compromise between both agronomic and engineering influences; however, the resulting product has limited functionality because of differences in definitions between engineering and agronomic grain sizes and non-alignment with soil textural classes. Consequently, classification and use of the family taxon have largely been ignored. Some adjustments to the family taxon for mineral soils and terric layers in organic soils are proposed including realignment of classes in the current family particle-size triangle to follow the divisions of the soil textural classes. Minor adjustments to mineralogy classes and depth to bedrock are also proposed.

Radiation level, radionuclide distribution and mineralogy of soils in Belagavi region of Karnataka, India

ABSTRACT The paper presents the results of systematic investigations on the gamma dose rates in air, natural radioactivity in soil and the dependence of radioactivity on the mineralogy of soils in the environs of the Belagavi, Karnataka, India. The gamma dose rates were measured using a portable survey metre and the activity in soils were measured using NaI(Tl) based gamma ray spectrometer and the mineral composition was studied using FTIR spectroscopy. The activity of 40K varies from 72.52 to 324.76 Bq kg−1 with an average of 153.17 Bq kg−1. The 226Ra activity varies from 16.53 to 70.53 Bq kg−1 with an average value of 23.88 Bq kg−1 and the activity of 232Th varies from 10.95 to 59.07 Bq kg−1 with an average value of 25.75 Bq kg−1. Elevated levels of 226Ra, 232Th and 40K in soils were observed in some part of Belagavi, which was traced to the mineralogy of the region. The higher activity of natural radionuclides poses radiological implications to the population of the region. The activity utilisation index was found to be is above the normal levels in some locations. The pattern of distribution of radionuclides in the region was studied using SPSS statistical software. The soil with clay minerals Haematite, Calcite, Kalonite, Albite and Feldspar showed higher radionuclide content.

Soil Mineralogy and Applied Phosphate Transformation in a Toposequence of a Tropical Semi-arid Landscape: Montgomeryite [Ca2Al2(PO4)3(OH).7H2O] as the Possible Metastable Phosphate Transformation Residue

ABSTRACT The residual responses of crops to phosphate fertilizers in weathered soils depend on the mineralogy and the nature of the phosphate reaction residue formed by soil–phosphate interactions. The study examined the metastable phosphate residues formed from soil-phosphate interactions along a tropical semi-arid toposequence by solubility criteria principles after soil-phosphate incubation for 28 weeks. The powder X-ray diffraction of the sand and silt-sized particles showed the dominance of K-feldspars in association with quartz and muscovite, while the oriented clay fractions indicated a preponderance of kaolinite and illite derived from the weathering of K-feldspars that were the surviving primary silicates in the soils. Soil-phosphate incubation with 12.5 mmol P kg−1 for 28 weeks showed, by the 7th week, phosphate, , activities in apparent equilibrium with montgomeryite, Ca2Al2(PO4)3(OH).7(H2O), solubility at pH ≥ 6.0. After 28 weeks, the HPO4 2- activities were in apparent equilibrium with hydroxyapatite, Ca5(PO4)3OH at the pH range of 6.5 to 7.2. The study provides an indirect evidence of the existence of montgomeryite as the potential metastable phosphate residue of soil-phosphate reactions in these slightly acid tropical semi-arid soils, before reverting to the more stable hydroxyapatite with time.

Unravelling causes of poor crop response to applied N and P fertilizers on African soils

Summary A number of studies across sub-Saharan Africa have recently reported poor crop responses and low agronomic use efficiencies of applied nitrogen (AEN), phosphorus (AEP) and potassium (AEK). However, the conditions under which non-responsiveness occurs, its underlying causes and its probability of occurrence on different soil types are not well understood. Using data from 542 sites and 14 soil types in 23 African countries, we provide novel insights into the linkage between lack of response to applied N, P and K, the mineralogy of soils and their resilience to erosion. We estimated mean responses as well as the probabilities (ϕ) of no response in terms of response ratio (RR), yield gain (YG) and agronomic efficiency. Here we defined ‘no response’ as zero agronomic response to fertilizer inputs in a given site and year indexed by either RR ≤ 1, AEN ≤ 0, AEP ≤ 0 or AEK ≤ 0. The highest risks of no response were recorded on the iron-rich Plinthosols (ϕ = 0.26) followed by the aluminium-rich Alisols (ϕ = 0.16) and the erosion-prone Lixisols (ϕ = 0.16) and Leptosols (ϕ = 0.13). In terms of yield gains, the highest risk of low response (i.e., YG ≤ 0.5) was recorded on Alisols (ϕ = 0.47) and the lowest on Fluvisols (ϕ = 0.05). Cambisols, Fluvisols, Luvisols and Nitisols were deemed highly responsive to NPK fertilizer. The risks of no response were significantly higher on soils derived from siliceous than mafic parent materials, soil types with low resilience to erosion, soils with low-activity clays and high P fixation capacity. It is concluded that maize grain yields can exceed 3 t ha-1 with high probability (ϕ &gt; 0.80) on Andosols, Nitisols and Vertisols, but with very low probability (ϕ &lt; 0.30) on Alisols and Arenosols. It is also concluded that across soil types and agroecological zones, the risk of no response is up to two times more on farmers’ fields than on research stations. Here, we discuss the implications of these finding for the design and location of future agronomic trials. We also provide insights to guide the targeting of fertilizer subsidies where nutrients can be more efficiently used.