Soil Mineralogical Properties Research Articles

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.

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.

Using proximal sensors to assess pedogenetic development of Inceptisols and Oxisols in Brazil

Proximal sensors like portable the X-ray fluorescence (pXRF) spectrometer, visible and near-infrared spectrometer (Vis-NIR) and magnetic susceptibilimeter have been increasingly used for the acquisition of complementary data to investigate chemical, physical and mineralogical properties of soils. Through the association between these sensors, this study aims to differentiate classes of soils with similar pedogenetic development, but developed from different parent materials. Four soil profiles were described and sampled in Lavras, Minas Gerais, Brazil: Oxic Dystrustept and Anionic Acrudox, developed from gabbro and Typic Dystrustept and Rhodic Hapludox, developed from gneiss. Samples from the A, B and C horizons were subjected to analyses by pXRF, Vis-NIR, and magnetic susceptibility, in additon to their physicochemical characterization and determination of their mineralogy via X-ray diffraction (XRD). The contents of Si, Fe and Ti obtained by pXRF as well as the MS values were decisive in distinguishing soil classes according to the parent material. The spectral curves generated by Vis-NIR showed different spectral responses for the same soil class due to their differential mineralogical constitution. Soils developed from gabbro had higher contents of iron oxides and a low reflectance in relation to the soils developed from gneiss. The proximal sensors contributed to the differentialtion of soil properties both within soils developed from the same parent material, mainly expressing their different weathering degrees, and within soils of the same taxonomic order, but developed from distinct parent materials. These proximal sensors can improve the characterization of soils and evaluations about their genesis at reduced time and costs.

Clay mineralogy fingerprinting of loess-mantled soils on different underlying substrates in the south-western Poland

Loess may be integrated into slope deposits at different soil depths and may influence related physical, chemical and mineralogical soil properties. Therefore, tracking the border between deposited loess and underlying materials and estimating the depth of loess penetration is a challenge. Five soils from the Lower Silesia province in south-western Poland having different types of geologic substrate and being covered by loess deposits of various thicknesses were chosen to: 1) trace the origin of phyllosilicates in these heterogeneous soils (loess vs. underlying bedrock); 2) determine the influence of the geologic substrate and the loess mantle on clay mineral transformation in the soil; and 3) relate clay mineralogical traits to soil morphology. The loess consisted of long-distance and local aeolian sources as shown by the Ti/Zr ratios and heavy mineral composition. Geochemical and mineralogical traces of loess were easily detected in the mixed zone and in part also in the basal layer. The loess deposits are characterised by mica, chlorite, kaolinite, interstratified mica-vermiculite or hydroxy-interlayered vermiculite, vermiculite and a minor amount of smectite. Aeolian silt admixture was an important source of chlorite at all sites. The vertical distribution of mica indicated two types of sources — loess input and substrate. Smectite, however, has mostly been inherited from the underlying bedrock (serpentinite, glacio-fluvial deposits and basalt slope sediment) or was formed in the soils from mica or chlorite. Where present in the loess, smectite was only found in small amounts. The presence of kaolinite, HIV and mixed layered mica-vermiculite could be derived either from aeolian input or neoformation and thus actively occurring mineral (trans)formation reactions. Similar to mica, vermiculite was derived from both aeolian input and the geological substrate. The widespread loess deposits in this region rejuvenated the soil formation process, as evidenced by their mineralogical and chemical composition.

Long-term effects of irrigated agriculture on Luvisol pedogenesis in semi-arid region, northeastern Brazil

Long-term irrigation in semi-arid regions leads to shifts in the soil moisture regime, affecting soil attributes and pedogenesis. Drylands are expected to increase worldwide, possibly because of climate change. Few studies have investigated changes in the pedogenic processes due to extensive irrigation in the Brazilian semi-arid region. This study assesses the effects of land use changes (irrigation and cultivation) on the morphological, physical, chemical, and mineralogical properties of soils. We evaluated two soil profiles in the semi-arid region in northeastern Brazil. We investigated an irrigated profile (IP) with long-term irrigation (26 years) and cultivation, and another profile under natural conditions (rain-fed hyperxerophilic Caatinga), that is, a non-irrigated profile (N-IP). The results indicate that land use affected chemical and mineralogical attributes of soils as well as the pedogenetic processes. Both soil profiles showed different behaviors in relation to salts: (1) reduction in soil exchangeable Na content (solodization) in IP, and (2) accumulation of soluble salts (salinization) and increased soil exchangeable Na content (solonization) in N-IP. Land use, possibly irrigation, induced mineralogical alteration pathways, such as the progressive mineral transformations via R0 MLM (mixed-layered minerals), suggesting differences in weathering and mineral evolution. The K-I (kaolinite-illite) and I-V (illite-vermiculite) phases predominated in the clay fraction in both soils and exhibited a greater trend for progressive kaolinization in IP. The other two MLMs (kaolinite-vermiculite, K-V and illite-smectite, I-S) were detected in N-IP and could be a proxy for the lowest weathering degree. This is consistent with the trend for a slight reduction in the SiO2/Al2O3 molecular ratio in IP. Illite was possibly the precursor mineral for other phyllosilicates, such as kaolinite, in IP. Fe-enriched MLM was detected in the decreasing sequence: illite, smectite, and kaolinite layers. The pedogenic trends observed, such as mineral weathering, may be attributed to system response to climate change.

A review of the mineralogical and geotechnical properties of some residual soils in relation to the problems of road failures: A case study of Nigeria

Poor geotechnical and mineralogical properties of soils used for road construction are a significant factor responsible for pavement failures. This is because most soils encountered at failed portions of some pavements do not meet the specifications according to relevant standards. It is with this in mind that this study carried out a systemic review on some residual soils in Nigeria, with a focus on their locations, geotechnical, and mineralogical properties in comparison to standards specified in the Nigerian specification for road and bridges. This study also reviewed how these properties have contributed to various road failures in different regions of the country. It was observed that the geotechnical and mineralogical properties of most residual soils in some regions of Nigeria did not meet up with the standards stipulated by the Nigerian Specification for road materials. Reviews carried out on the place of geotechnical and mineralogical characteristics on various road failures in Nigeria showed that a high volume of research works was carried out in the south-western and southeastern parts of the country compared to the Northern region.

Geochemistry of soils of a deep pedon in the Okavango Delta, NW Botswana: Implications for pedogenesis in semi-arid regions

Pedogenic parameters and data on geochemical compositions were analysed to improve our understanding of pedogenesis and soil morphology in an ecologically and geologically unique and relatively quiescent tectonic setting of the Okavango Delta, northern Botswana. A complex interaction of pedogenic and gradational processes in the area resulted in the formation of a deep (~4 m) pedon with three distinct morphologies: a weakly structured surface horizon, modern pedogenic carbonate enriched B horizons at stage III development and slightly pedogenically altered sediment C horizons. The pH ranged from 8.1 to 10.0 implying alkaline soil environment, while electrical conductivity ranged from 2 to 55 dS/cm. Gleying, an evidence hydromorphism, was present in the wetting front (C horizon). Results of the total elemental composition show the dominance of silica followed by CaO, Al2O3, MgO and Fe2O3 as the major oxides. Trace elements had lower HFSE (e.g. Zr and Nb) than LILE (e.g. Ba, Sr, Rb, Cr and V) contents. Calcite, quartz and opal-CT are the minerals present in the fine silt and clay fractions of the soils. Geochemical indicators points to incipient weathering and pedogenesis. Evolutionary accumulation of pedogenic carbonate in the diagnostic horizons bestows Calcisols as the Reference Soil Group and not Arenosols as previously known. Other pedogenic processes including leaching losses, redox processes and salt accumulation were strongly influenced by the saline groundwater processes. By comparing these site-specific findings with examples from other settings, this study has demonstrated the applicability of morphological, geochemical and mineralogical properties of soils in assessing pedogenic processes and classification in deep calcic soils associated with alluvial and aeolian depositions.

Analysis of the Physicochemical and Mineralogical Properties of the Materials Used in the Preparation of Recoblocks

The construction sector generates 14,000 t/d of construction waste in Mexico City, these materials do not have real applications and end up accumulating in landfills. This work, the objective of which was to analyze the physicochemical and mineralogical properties of soil and construction waste used in the manufacture of Recoblocks, is divided in five stages. First, the excavation material was submitted to field tests. Physical and chemical tests were then carried out on construction waste. Subsequently, the optimal mixture for making Recoblocks was determined. Next, Recoblocks were evaluated and compared with blocks made with water only, without mucilage of Opuntia ficus, and finally a feasibility study was performed. The X-ray diffraction study showed the presence of plagioclase, minerals that improve bending resistance, hardness, durability, as well as resistance to stress in a material. Compared to blocks manufactured without mucilage, the use of Opuntia ficus mucilage increased the compressive strength of the material by 59%, as well as the erodibility. Recoblocks are an environmentally friendly option because they are based on recycled materials, dried under the sun, which eliminates the use of brick oven. The production cost per unit is just USD 0.19, so it is a viable option as a building material.

Influence of Toposequence on Physical and Mineralogical Properties of Soils Developed on Basaltic Parent Material under Sub-humid Terrestrial Ecosystem

Understanding of soil forming factors is crucial to define physical, mineralogical and morphological properties of soils. In addition to that soil formations were highly associated with slope positions which have influence on pedogenetic and weathering process of the soils. Because, topography or relief affects how water and other material are added to and removed from soils. The aim of this study is to enhance our understanding of the role toposequence in controlling chemical weathering, influence on physical and mineralogical properties in soils developed on basaltic parent material under sub-humid terrestrial ecosystem in Black Sea region of Turkey using geochemical and mineralogical data obtained from X-ray diffraction and Scanning Electron Microscope analysis. For this purpose, four representative profiles formed on different topographic positions of transect were investigated and designated according to Soil Survey Staff (2014)/IUSS Working Group WRB (2015) classification systems. The results clearly showed that topography strongly affects soil physical, mineralogical and morphological characteristics either directly or indirectly in the local region even soils formed on the same parent material with the same climatic condition. This case was also explained with chemical weathering indices (Chemical Index of Alteration and Chemical Index of Weathering) in this study.

Cellular and extracellular C contributions to respiration after wetting dry soil

Wetting of dry soil triggers a pulse of microbial respiration that has been attributed to two broad mechanisms: (1) recycling of microbial cellular carbon (C), and (2) consumption of extracellular organic C made available to microbes by wetting. We evaluated these two mechanisms by measuring cumulative CO2 release, changes in the size and chemical composition of microbial biomass, and water-extractable organic carbon (WEOC) concentrations following artificial wetting of soil sampled from two depths at each of seven sites across California spanning a range of geologic parent materials. In samples collected from surface soil (0–10 cm depth), we found that cumulative CO2 release after wetting in the laboratory was most strongly correlated with microbial biomass. In these samples, the relative abundance of trehalose—a putative microbial osmolyte—decreased from 25% (SD = 12) to 16% (SD = 7) of the chloroform-labile fraction of the microbial biomass after wetting. This suggested a role for osmolyte consumption in generating the respiration pulse. In subsoil (40–50 cm depth, or sampled at contact with rock), however, the cumulative CO2 release after wetting was unrelated to microbial biomass and more strongly related to WEOC. The concentrations of selected microbial biomass constituents (e.g. trehalose and amino acids) in WEOC were negligible (< 1%), suggesting that cell lysis was not important in generating WEOC in this study. The amount of WEOC relative to total organic C was greatest in subsoil, and negatively related to ammonium oxalate-extractable Fe (Pearson’s R = 0.42, p < 0.01), suggesting a role for soil mineralogical properties in controlling WEOC release. Together, these findings suggest that microbial cellular C and extracellular C jointly contribute to the respiration pulse, and that their relative contribution depends on depth.

Enzyme activities as affected by mineral properties in buried volcanic soils of southern Italy

The aim of the study was to explore the likely relationships between physico-chemical and biochemical properties in buried volcanic soils of Italy, showing different degree of andic properties extent. Indeed, buried soils have the advantage to be less directly affected by anthropic impact, fresh carbon (C) inputs and environmental conditions (such as temperature, humidity, pH etc.). Two soil chronosequences, developed in different volcanic geomorphological environments, were analysed in Campania region (Italy) to assess the variations of biochemical properties according to soil andic properties. Chemical properties enabled to classify these soils as Andosols of silandic type (e.g. dominated by imogolite-type materials – ITM). As regards the relationship between soil mineral properties and biochemical activity, a positive correlation was found between enzymes and Alpy but not with Feox, Siox or ITM content. However, acid phosphomonoesterase, chitinase, leucine aminopeptidase, arylsulphatase, butyrate esterase activities and enzymes involved in C cycle (SEIc) were significantly different among soils, showing higher activity rates in soils with more pronounced andic properties. Conversely, when enzyme activity was expressed per unit of organic C (specific enzyme activity) it was significantly higher in weakly andic soils. The specific enzyme activity was particularly sensitive to the increase of Alox + 1/2Feox only for values <1%, typical of low developed andic properties, pointing to an important role of Al in controlling the interactions between the ITM mineral phase and soil enzymes. In conclusion, the soil mineralogical properties influenced the potential hydrolysis of organic C whose stabilization in the soil matrix may be affected by ITM presence and the stable interaction with soil enzymes. However, in order to establish if soils’ biochemical activity may be affected by andic properties, additional research should be addressed to cover all types of Andosols, including the aluandic ones.

Mineralogy of Soils along Toposequence in Raipur District of Chhattisgarh

The mineralogical compositions along with physical, chemical, elemental and mineralogical properties of four pedons occurring along a toposequence in Chhota Urla village (Abhanpur tehsil), Raipur district of Chhattisgarh state were studied. Landform had significant influence on physical, chemical, elemental and mineralogical properties of soils. Sand content decreased from higher topography to lower topography but clay content increased with decrease in elevation. pH of pedons ranged from strongly acid to moderately alkaline and CEC increased from upland to lowland. Quartz being dominant in sand fraction and absence of primary minerals like Ca-feldspar, K-feldspar indicated intense weathering of soils. Silt had quartz as dominant mineral followed by Ca- feldspar and K-feldspar. Kaolin was dominant mineral in clay fractions of pedons l and 2 (PI and P2) with sub-ordinate amount of smectite while smectite was dominant in other two pedons followed by kaolin. Huge amount of smectite which is first weathering product of plagioclase, did not find its parental legacy with underlying geology (sandstone, limestone and shale sequence) indicative of mixed alluvium, eroded from different geological formation and contradicted the occurrence of catenary sequence as reported earlier.

Do Aggregate Size Classes of the Subsurface Soil Horizon Have Different Chemical/Mineralogical Properties?

ABSTRACT Variations in chemical and mineralogical properties of a soil can occur at short vertical and horizontal distances. The objective of the present study was to evaluate the chemical and mineralogical soil properties of different aggregate classes from young (Ustrochrept) and highly weathered (Acrustox) soils from the state of Parana, Brazil. Undisturbed blocks (0.20 ×0.20 ×0.20 m) of soils were separated into aggregate classes: Acrustox – 8.0-4.0 mm; 4-2 mm; 2.0-0.5 mm; 0.5-0.2 mm; and <0.2 mm; and Ustrochrept – [...]

Influence of Clay Minerals on Some Soil Fertility Attributes: A Review

Clay minerals constitute an important component of the soil system and knowledge of their role in soil fertility is imperative for sustainable soil management and productivity. The aim of this work is to overview the influence of clay minerals on some major soil fertility attributes. The rationale for carrying out this work is that most soil fertility studies rarely incorporate soil mineralogy. Clay minerals, through their physical and chemical properties, affect soil fertility by controlling nutrient supplies and availability, through the sequestration and stabilization of soil organic matter, by controlling soil physical properties through microaggregate formation, by influencing soil acidity and controlling soil microbial population and activity. The main processes involved in these relationships are dissolution-precipitation and adsorption-desorption processes, alongside mechanisms involving the formation of short-range-ordered phases. Although the determination of soil mineralogical properties is very costly and time-consuming, information about a soil’s mineralogy is imperative for a holistic understanding and proper management of soil fertility. Therefore, the development of rapid, low-cost, reliable and efficient techniques of soil mineralogical analysis, directly applicable to soil fertility investigations, constitutes a major challenge. Also, future research should investigate the relationships between clay minerals and soil nitrogen vis-a-vis sequestration and stabilization. Lastly, clay minerals should be considered in studies dealing with soil quality assessment, especially in the choice of soil quality indicators.

Soil Evolution and Mass Flux of Basaltic Cinder Cones in a Cool, Semi‐Arid Climate

Core Ideas Soil development across a chronosequence of basaltic cinder cones. Elemental mass balance data were used to investigate secondary mineral formation. Elucidate rates and processes of early stage weathering. Soil developmental processes on young volcanic cinders in cool, semiarid climates are not well understood and previously under‐studied, but present a unique setting within which to study neoformation of soils under well‐dated time constraints. This study investigates the development of physical, chemical, and mineralogical soil properties on a chronosequence of basaltic cinder cones, aged approximately 2.1, 6.9, and 13.9 ka, at Craters of the Moon National Monument and Preserve in southern Idaho. Representative parent material, coarse fragments, and soil samples were analyzed using selective dissolutions and total elemental digests. Elemental mass balance data were used together with the soil physicochemical data to investigate weathering and secondary mineral formation within each soil profile. The highest degree of weathering was identified on the 13.9 ka profile, followed by the 6.9 and 2.1 ka soils. Short‐range ordered minerals, including allophane and ferrihydrite, dominate the colloidal fraction of all soils, with greatest proportions in the oldest soil. Dominant soil‐forming processes documented along the chronosequence of basalt‐derived soils are the accumulation of organic carbon, weathering of rock fragments, loss of base cations, redistribution of Fe, Al, and Ti, and the accumulation of secondary short‐range order and crystalline minerals. This study provides critical information to elucidate rates and processes of early stage weathering, dust influence, and soil evolution on cinders in cool and dry climates.

Physical Properties of Soils from Several Land Uses in a Tidal Swampland Area Applied with a Fork Irrigation System

In Indonesia, tidal swampland is potential to be developed into agricultural land uses. Water management is the key success of farming on the tidal swampland. In the tidal swampland of Kalimantan, Indonesia, a fork irrigation system is widely applied in the water channels to supply irrigation water to the land. Besides irrigation, soil physical characteristics play an important role in controlling water availability for crops. The ability of soil to store water will determine the amount of available water that can be taken up by plants. This research aimed to determine the soil physical properties that are related to water availability in the soils from different land uses in a tidal swamp land area applied with a fork irrigation system. The experiment was conducted in dry season 2012, in Belawang, Barito Kuala district, South Kalimantan province. The soil samples were taken from four land uses, namely rice field, rubber plantation, mixed cropping, and unmanaged land. The soil physical properties, namely soil bulk density, particle density, porosity, texture, pF 1, pF 2, pF 2.54, pF 4, water content, total pore space, rapid drainage pores, slow drainage pores, available water, groundwater level were measured. In addition, the mineralogical properties of the soils were measured as well. The results showed that the physical properties of the soils taken from different land use varied, however, the change of the land use did not cause changes in the soil mineralogical properties. The mineralogy of the soils from different land uses are relatively the same, namely: quartz, illite, and chlorite.

Mineralogical analysis of ferralitic soils in Madagascar using NIR spectroscopy

The applicability of near-infrared reflectance spectroscopy (NIRS) as tool for estimating mineral soil constituents was assessed over a wide range of highly weathered soils in Madagascar. The predictions were based on two types of methods, chemometric methods using multivariate calibration models from partial least squares (PLS) regressions, and the use of spectral signatures of specific minerals. The predictions of mineralogical properties of soils using chemometric methods were poor, except for the quantification of iron oxides extracted with citrate-bicarbonate dithionite (CBD) (R2cv=0.80). Soil minerals (kaolinite, gibbsite, goethite and hematite) were also estimated by NIRS but with less accuracy (R2cv=0.50–0.80). The predictions of kaolinite and gibbsite contents were improved by the use of the peak intensity of the first derivative spectra, situated at around 2205nm for kaolinite and 2265nm for gibbsite. The results indicate that NIRS can be used as a rapid analytical technique to simultaneously estimate the main minerals of highly weathered ferralitic soils with acceptable accuracy.

Microbial utilization of mineral-associated nitrogen in soils

In soils, a large portion of organic nitrogen (ON) is associated with minerals and thus, possibly stabilized against biological decay. We therefore tested if mineral-associated N is an important N source for soil microorganisms, and which soil parameters control its bioavailability. Microcosm experiments with mineral-associated organic matter, obtained as heavy fraction (HF) via density fractionation, and bulk soil from mineral topsoil of the Franz Josef chronosequence were conducted for 125 days. We examined the effects of O2 status, soil age (differences in mineralogical properties), as well as cellulose and phosphate additions on the turnover of mineral-associated N. Using a combination of activity measurements and quantitative PCR, microbial N transformation rates and abundances of N-related functional genes (amoA, narG, chiA) were determined. Similar or higher values for microbial N cycling rates and N-related functional abundances in the HF compared to bulk soil indicated that mineral-associated N provides an important bioavailable N source for soil microorganism. The turnover of mineral-associated N was mainly controlled by the O2 status. Besides, soil mineralogical properties significantly affected microbial N cycling and related gene abundances with the effect depending on the N substrate type (ON, NH4+ or NO3−). In contrast, cellulose or phosphate addition hardly enhanced microbial utilization of mineral-associated N. The results of our microcosm study indicate that mineral-associated N is highly bioavailable in mineral topsoils, but effects of the mineral phase differ between N cycling processes.

Pedogenesis across a climatic gradient in tropical high mountains, Cordillera Blanca — Peruvian Andes

Studies in alpine environments have shown that chemical weathering and clay mineral formation are mainly controlled by climate and vegetation. However, few studies have focused specifically on pedogenesis in tropical high mountains. We evaluated pedogenic processes and weathering intensity by physical, chemical and mineralogical properties of soils under different vegetation types across a climatic gradient (east/west) in the Northern Cordillera Blanca, Peru. We established 2 catenas and sampled 10 pedons - 6 at Llanganuco valley (east-dry) and 4 at Portachuelo valley (west-wet). Pedons from both catenas are formed on colluvial deposits, gravelly and weakly developed, showing a sequence of O, A, C and C/R horizons. Lithological discontinuities in all pedons revealed sequences of buried A horizons. They also shared the same soil forming processes related to organic matter accumulation, such as humification, melanization and formation of organometallic complexes. The uppermost horizons show high values of total organic carbon and are dark colored. In general, pedons are acidic to slightly acidic, have a low base saturation, a high Al saturation and low effective and potential cation exchange capacity. Seven pedons were classified as Umbrisols, one Fluvisol, one Leptosol and one Regosol. Their similarity is attributed to environmental instability, not allowing sufficient time to develop further. However, pedons at Portachuelo valley showed higher weathering intensity revealed by crystalline iron oxide formation and transformation of phyllosilicates minerals. Among them, pedon under Polylepis forest showed the highest weathering intensity, which favored transformation of chlorite to mixed-layered minerals, suggesting that combined climate and vegetation control chemical weathering and mineral transformation.