Resumen Pitanga (Eugenia uniflora L.) es una fruta exótica de gran importancia económica por su alto potencial de uso. Sin embargo, debido a su variabilidad genética, su explotación se ve dificultada por no presentar producción de frutos homogénea. En este contexto, este estudio tuvo como objetivo seleccionar genotipos de pitanga de acuerdo con las características físicas y fisicoquímicas de los frutos en condiciones semiáridas. Se desarrolló en la Universidad Federal Rural del Semiárido y los genotipos se originaron a partir de la polinización abierta de la variedad pitanga ‘Tropicana’. Se evaluaron 39 genotipos de pitanga con respecto a los siguientes rasgos: masa de fruto (g), longitud y diámetro de fruto (mm), sólidos solubles (SS, °Brix), acidez titulable (AT), ácido ascórbico (AA), pH y Relación SS/AT. Los genotipos de pitanga presentaron alta variabilidad. El agrupamiento permitió separar los genotipos de acuerdo con los rasgos deseables. El genotipo A12 presentó frutos de mayor calibre, y el genotipo A8 presentó los mayores contenidos de SS y AT. Los genotipos A2, A13, A34 y A39 presentaron altos valores de AT. Los genotipos A11, A16, A45, A9, A26 y A44 presentaron los contenidos más significativos de pH y relación SS / AT en los frutos.

Abstract Pitanga (Eugenia uniflora L.) is an exotic fruit species of significant economic importance. However, due to genetic variability, its exploitation is hampered by the lack of homogeneous fruit production. In this scenario, this study aimed to select pitanga genotypes according to the physical and physicochemical parameters of fruits grown under semi-arid conditions. The study was developed at the Federal Rural University of the Semi-Arid Region with genotypes resulting from the open pollination of the pitanga variety ‘Tropicana”. Thirty-nine pitanga genotypes were evaluated for fruit mass, fruit length, fruit diameter, soluble solids (SS), titratable acidity (TA), ascorbic acid (AA), pH, and SS/TA ratio. The pitanga genotypes showed high variability. The clustering method separated the genotypes according to desirable traits. Genotype A12 showed the largest fruit sizes, whereas genotype A8 showed the highest SS and TA contents. Genotypes A2, A13, A34, and A39 showed fruits with the highest AT values. On the other hand, genotypes A11, A16, A45, A9, A26, and A44 showed the most significant contents of pH and SS/TA.

ABSTRACT Phosphorus availability in soils is low due to its strong retention by inner-sphere complexation on minerals in the clay fraction with pH-dependent charges, such as goethite. On the other hand, sulfur has greater availability because it is retained mainly by electrostatic attraction. We evaluated the intensities of the inner-sphere complexation of orthophosphate and sulfate (H2PO4-/HPO42- and SO42- - generically treated as PO4 and SO4) under different experimental conditions (pH, goethite purity, and contact times) on synthetic goethite samples to establish the mechanisms and models involved in those bonds. Inner-sphere PO4 and SO4 were extracted using both HNO3 1 mol L-1 and USEPA 3051A methods. Inner-sphere complexation of PO4 and SO4 was highest at pH 5 in relation to pH 9. Attenuated total reflectance/Fourier transform infrared spectroscopy (ATR-FTIR) spectra showed inner-sphere complexation bands of PO4 on goethite in the protonated binuclear bidentate (pH 5) and deprotonated binuclear bidentate (pH 9) forms. Inner-sphere complexation of PO4 was much more expressive than that of SO4. Phosphorus and sulfur oxyanions displace the diprotonated ferrol ligand (-OH2+0.5 in -FeOH2+0.5), while the -OH-0.5 in the -Fe-OH-0.5 group are only displaced by PO4. The -O-1.5 ligand in Fe-O-1.5 group is not displaced by PO4 or SO4. The high surface negative charge density of PO4 defined its higher activation energy for exchanging -OH2+0.5 and -OH-0.5 on the goethite surface in relation to SO4. The proposed model can be used to reduce inner sphere phosphate adsorption in soils and improve P fertilization efficiency for farming.

RESUMO A figueira (Ficus carica L.) é amplamente aceita devido às suas propriedades organolépticas e farmacológicas. A busca por inovações para aprimorar o manejo da cultura tem aumentado para reduzir os impactos ambientais e melhorar a qualidade organoléptica e a segurança alimentar dos frutos. Assim, este trabalho teve como objetivo avaliar a influência de métodos de fertilização e sistemas de treinamento de plantas na produção e nas características físico-químicas da figueira. O experimento foi conduzido em delineamento de blocos casualizados em esquema fatorial 5 × 4, com três blocos e três plantas por parcela. Os fatores corresponderam a cinco fertilizantes (químico, esterco bovino, esterco ovino, cama de aviário e composto orgânico) e quatro sistemas de treinamento (dois ramos, três ramos, quatro ramos e espaldeira). Os resultados mostraram que, com o uso de fertilizante químico e cama de frango, as plantas apresentaram produção, rendimento e número de frutos semelhantes, com firmeza, comprimento e cor de casca semelhantes (L e °h). A maior produtividade e número de frutos imaturos foram obtidos com esterco bovino. O teor de sólidos solúveis e a relação teor de sólidos solúveis / acidez titulável foram maiores nos frutos provenientes de plantas fertilizadas com esterco bovino, esterco ovino e composto orgânico. Por outro lado, plantas treinadas com três e quatro ramos ou em espaldeira produziram frutos com maior teor de sólidos solúveis e peso. Além disso, frutos mais pesados foram obtidos usando fertilização química e plantas condutoras com dois, três e quatro ramos.

ABSTRACT Fig (Ficus carica L.) is widely accepted due to its organoleptic and pharmacological properties. Search for innovations to improve the crop management has increased to reduce environmental impacts and improve the organoleptic quality and food safety of the fruits. Thus, this study aimed to evaluate the influence of fertilization methods and plant training systems on the production and physicochemical traits of fig. The experiment was carried out in a randomized complete block design in a 5 × 4 factorial scheme, with three blocks and three plants per plot. The factors corresponded to five fertilizers (chemical, cattle manure, sheep manure, poultry litter, and organic compost) and four training systems (two branches, three branches, four branches, and espalier). Results showed that, when using chemical fertilizer and poultry litter, plants showed similar productivity and number of fruits, which had similar firmness, length, and peel color (L and °h). The highest production and number of immature fruits were obtained using cattle manure. Soluble solids content and soluble solids content/ titratable acidity ratio were higher in fruits from plants fertilized with cattle manure, sheep manure, and organic compost. On the other hand, plants trained with three and four branches or in espalier produced fruits with the highest soluble solids content and weight. Also, heavier fruits were obtained using chemical fertilization and conducting plants with two, three, and four branches.

ABSTRACT The combination of pillarization and charge neutralization with Li+ can make montmorillonite an important support material for industry and decontamination of pollutants in soil and water. Montmorillonite characterization techniques were described in detail, and pillarization procedures were used, after Li+ saturation, to modify and manipulate the chemical and mineralogical surface properties of this montmorillonite. Eight samples were produced: 1) natural montmorillonite (Chisholm Mine - MMT); 2) Li+ saturated montmorillonite (MMTLi); 3) polyethylene glycol (PEG) Al-pillared montmorillonite (AlPEG); 4) PEG Al-pillared montmorillonite saturated with Li (AlPEGLi); 5) Al-pillared montmorillonite with 14 h contact time (Al14h); 6) Al-pillared montmorillonite Al14h saturated with Li (Al14hLi); 7) Al-pillared montmorillonite with 0 h contact time (Al0h); and 8) Al-pillared montmorillonite Al0h saturated with Li (Al0hLi). The natural sample was identified as interlayered montmorillonite composed of chlorite layers or with a high degree of Al-hydroxy filling. Concerning the total permanent charges, 70 % occurred by isomorphic substitution of Al3+ by Mg2+ in octahedral layer and 30 % of Si4+ by Al3+ in tetrahedral layer. The pillarization method using the PEG produced a small number of stable pillars. The new milder pillarization method (Al0h) did not cause damage in the formation of Al-hydroxy. In this method, the resulting pillars were more homogeneous in size. Thereby, the Al0h Li method has been shown to produce a supporting material with a constant interlayer spacing, increased of the specific surface area (SSA), and drastic reduction of the cation exchange capacity (CEC) as compared to MMT. This modified mineral can be used in, for example, decontamination of polluted water with nonionic organic pollutants.

RESUMO É comum o uso dos métodos 3051A e água régia para avaliar o teor pseudo-total e total de P nos solos e em suas frações. No entanto, estudo anterior mostrou a formação de grandes quantidades de materiais de baixa ordem estrutural (MBOE) nos resíduos dessas extrações. O objetivo deste trabalho foi avaliar se ocorre readsorção de fosfato no MBOE dos resíduos das extrações 3051A e água régia na fração argila de solos. Os resíduos obtidos a partir do 3051A e água régia foram recuperados dos papéis de filtro. Para caracterizar o MBOE nesses resíduos foram realizadas extrações sequenciais com oxalato de amônio 0,2 mol L-1 e NaOH 0,5 mol L-1. O teor máximo de P pseudo-total extraído pela água régia foi de 6800 mg kg-1. Se o MBOE formado durante a água régia não fosse extraída nesta amostra, 698 mg kg-1 de P não seriam contabilizados (subestimação de 10,3%). Esse alto nível de readsorção de P na extração 3051A e água régia leva a interpretações equivocadas da reserva de nutrientes na fração argila. A readsorção de fosfato foi principalmente no MBOE extraído pelo oxalato de amônio nos resíduos 3051A e água régia. O ambiente químico das extrações 3051A e água régia facilitou a readsorção por esfera interna de H2PO4 - nos grupos ferrol e aluminol do MOBE-oxalato de amônio. Houve maior reabsorção de H2PO4 - no 3051A-NaOH em relação ao NaOH-água régia.

ABSTRACT It is common the use of 3051A and aqua regia methods to assess the pseudo-total and total P contents in soil and in its fractions. However, previous study has shown the formation of large amounts of short-range order materials (SRO) in the residues of these extractions. The objective of this work was to evaluate whether phosphate resorb in the SRO formed in the residue of 3051A and aqua regia extractions in clay soil fraction. Residues obtained from the 3051A and aqua regia were recovered from filter papers. To characterize the SRO in these residues, sequential extractions were performed with 0.2 mol L-1 ammonium oxalate and 0.5 mol L-1 NaOH. The maximum pseudo-total P content extracted by aqua regia was 6800 mg kg-1. If SRO formed during this acid extraction was not extracted , 698 mg kg-1 P would have been not accounted (underestimation of 10.3%). This high level of P resorption in the 3051A and aqua regia extraction lead to misinterpretations of P reserve in clay fraction. Phosphate resorption was mainly in SRO extracted by ammonium oxalate for both 3051A and aqua regia residues. The chemical environment of the 3051A and aqua regia extractions facilitated the inner sphere adsorption of H2PO4 - in ferrol and aluminol groups of the SRO- ammonium oxalate. There was larger resorption of H2PO4 - in the 3051A-NaOH in relation to NaOH- aqua regia.

ABSTRACT Most of the forensic comparison of soils has focused on the clay and silt fractions at the expense of the coarser particles. This study aimed to test the potential of elemental and physical analyses in the sand fraction from subtropical soils to discriminate samples collected in areas under different parent material (claystone and marble) and in areas with the same parent material at a simulated crime scene. Scanning electron microscopy coupled to an energy dispersive X-ray spectrometer (SEM-EDS) analysis was used on the finer sized sand particles (0.05-0.25 mm). X-ray diffraction (XRD) and particle size distribution (PSD) analyses were performed on the whole sand fraction. These methods did not provide clear discrimination of the sand of the soils sampled in the subtropical environment. This can be explained by the large homogenization observed in the sand fraction related to its chemical (EDS), physical (particle size distribution), morphological (SEM), and mineralogical (XRD). Under tropical and subtropical conditions, the chemical weathering processes dissolve most of the primary minerals, such as the feldspars, biotite, and Fe-bearing particles, and concentrates quartz in the sand fraction. In these environments, we recommend the prioritization of the finer soil fractions for forensic studies, both inorganic and organic.

ABSTRACT Soil traces are useful as forensic evidence due to their potential to transfer and adhere to different types of surfaces on a range of objects or persons. Several works have been developed in forensic soils, under different analytical approaches. However, in Brazil, only the researches from the Group of the Federal University of Paraná have developed works with soils under a forensic approach. Focus has been given on the sequential chemical analyses and mineralogical techniques once they presented a large potential to discriminate soil samples, even that originated from the same bedrock. In this way, this work aimed to test a Standard Operating Procedure (SOP) for forensic soil sampling and an analytical protocol in Brazil between the academy and the scientific police through a blind simulated crime scene scenario. Samples were collected at four sites located in the Curitiba Metropolitan Region. All soils were classified as Inceptisol ( Cambissolo ), and the parent material in Curitiba is claystone and in Colombo is limestone. Around 3 g of sample composed by silt + clay fraction were isolated and analyzed by sequential chemical procedure: i) extraction of poorly ordered iron and aluminum oxides with ammonium oxalate (AO); ii) extraction of crystalline iron oxides with sodium dithionite-citrate-bicarbonate (DCB); and iii) extraction of poorly ordered aluminosilicates and gibbsite with NaOH 0.5 mol L-1. All data were transformed by square root and formed a data matrix subsequently analyzed in a principal component analysis (PCA). Most of the samples were properly grouped according to their provenance at all four sites tested, showing the potential of the Standard Operating Procedure (SOP) in a real crime scene. The sampling procedures presented in the SOP were detailed enough to allow the appropriate police work in forensic cases in any part of Brazil. As future considerations, modifications to the sample treatment and analytical protocol could be made depending on the context of the forensic work. Intense anthropogenic activities, such as domestic waste disposal in urban areas, would potentially reduce the discrimination power of such a proposed chemical analytical protocol.

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 Paraná, 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 – 8.0-4.0 mm; 4.0-2.0 mm; 2.0-0.5 mm; and 0.5-0.2 mm. The exchangeable K contents showed an opposite behavior for the two soils: higher contents in the Acrustox for the larger aggregate classes and higher contents in the Ustrochrept for the smaller aggregate classes. The crystallographic characteristics of hematite and goethite were variable according to the aggregate class. The goethite in the 2-4-mm aggregate class is expected to exhibit the highest reactivity for the Ustrochrept: lower growth and a more elongated form of the crystals. The smallest aggregate class presented the lowest contents of kaolinite and gibbsite in the clay fraction. Gibbsite and kaolinite in the intermediate classes presented higher growth in both soils. The studied soils present different side-by-side environments (aggregate classes) for the exploration by the root system. This means that for the precise identification of the environments explored by the roots of a single plant, field sampling should consider the aggregate class, obtained from an undisturbed soil sample. However, this is impractical in agricultural practice.

ABSTRACT Studies of heavy metals are concentrate on clay fractions, but coarser fractions of the soil can constitute significant sources of structural forms of heavy metals. The aim of this study was to evaluate the occurrence of heavy metals in the structure of minerals of the sand and silt fractions of soils from three different parent materials (metamorphic rocks and granite) in southern Brazil using SEM/EDS - Scanning Electron Microscopy with Energy Dispersive Spectroscopy and with WD-EPMA - with Wavelength Dispersive-Electron Probe Microanalysis. We sampled soils from two areas naturally rich in heavy metals, with high mineral deposits (galena - PbS) hosted in carbonate rocks and phyllite/mica schist. The main form of Ba in the sand and silt fractions was as barite (BaSO4). The precipitation of Ba and S from the soil solution occurred on the surface of silicate mineral particles. Due to the proximity of ionic radius of Ba-Pb, there was isomorphic substitution of Ba for Pb in the barite structure. The only primary mineral source of Pb in the coarse soil fractions was trioctahedral mica. Several secondary minerals in the silt and sand are sources of structural Pb: plumbogummite, plumboferrite, magnetoplumbite, and cerussite. There was a strong geochemical association of Pb-Fe-Mn. Zinc was also associated with Fe. The SEM/EDS/WD-EPMA techniques are important analyses to complement standard procedures, such as X-ray diffraction and total chemical digestion, in geochemical studies.

RESUMO. Alta disponibilidade de Al demanda maiores cuidados para tornar os solos aptos para a agricultura devido a toxidez para as plantas cultivadas. Contudo, as pesquisas sobre a relação entre a distribuição de Al em profundidade e o intemperismo do solo têm sido pouco priorizadas, principalmente aquelas conduzidas com um maior número de perfis de solos. O presente estudo analisou-se 38 solos ácidos selecionados dos levantamentos de solos da região Sul do Brasil, com o objetivo de identificar e isolar o efeito dos componentes orgânicos e minerais na distribuição em profundidade do Al trocável extraído com KCl (AlKCl). A seleção resultou na formação de três grupos de solos em relação aos teores de AlKCl em profundidade: Grupo I - diminuição; Grupo II - inexpressiva variação e; Grupo III - aumento. A matéria orgânica foi mais importante para determinar os altos teores de AlKCl na superfície dos solos mais intemperizados (grupo I) e a qualidade da fração mineral definiu os elevados teores de AlKCl nos horizontes subsuperficiais do grupo III. A distribuição de AlKCl em profundidade foi definida pelo grau de intemperismo do solo. O conhecimento desses agrupamentos de solo pode auxiliar no manejo da acidez do solo para otimizar a produtividade das culturas no sul do Brasil.

ABSTRACT. Due to potential crop toxicity, high aluminum (Al) availability requires increased attention when preparing agricultural soils. However, research examining the relationship between depth distribution of Al and soil weathering has received little priority in Brazil, particularly regarding the number of soil profiles investigated. This study analyzed 38 acid soils selected from Soil Surveys in southern Brazil to identify and isolate the effects of organic and mineral components on depth distribution of exchangeable Al extracted with KCl (AlKCl). These soil profiles were divided into the following three groups based on AlKCl depth distribution: Group I - decrease with depth; Group II - little variation with depth; and Group III - increase with depth. High AlKCl found near the surface of well-developed soils (Group I) was influenced by organic matter content, while mineral fraction quality defined the occurrence of high AlKCl in subsurface horizons of Group III. The depth distribution of AlKCl was defined by the degree of weathering in these subtropical soils. Possessing a knowledge of these soil groupings may aid in soil acidity management to optimize crop productivity in southern Brazil.

RESUMO Objetivou-se determinar a capacidade máxima de adsorção de As(V) na forma de HAsO42- (CMAAs) pela fração argila de solos em diferentes ambientes nas Penínsulas Keller e Barton, Ilha Rei George, Antártica Marítima. Foram realizadas análises química e granulométrica na terra fina seca ao ar, e na fração argila quantificou-se o material amorfo e a CMAAs. Os dados das análises químicas, granulometrica e da fração argila foram correlacionados com a CMAAs. A CMAAs foi baixa (3.554 mg kg-1), sendo o perfil com influência ornitogênica de pinguins o que apresentou os maiores valores. O pH básico das soluções de saturação não favoreceu a adsorção da espécie desprotonada HAsO42-. A quantidade de argila dos solos foi menos importante que a composição mineralógica na dinâmica de retenção de HAsO42-, sendo que os óxidos de Al e Fe amorfos foram os principais responsáveis pela adsorção desse poluente.

ABSTRACT The aim of this study was to determine the maximum capacity for the adsorption of As(V) in the form of HAsO42- (MACAs) by the clay fraction of soils in different environments of the Keller and Barton Peninsulas, King George Island, Maritime Antarctic. Chemical and particle size analyses were carried out on air-dried fine earth. The amorphous material and MACAs in the clay fraction were quantified. Data from the chemical analysis, particle size analysis and clay fraction were correlated with the MACAs. The MACAs was low (3,554 mg kg-1), with the profile under the ornithological influence of penguins displaying the highest values. The basic pH of the saturated solutions did not favour the adsorption of the deprotonated HAsO42- species. The amount of clay in the soil was less important than the mineralogical composition in the dynamics of HAsO42- retention, with the amorphous oxides of Al and Fe being mainly responsible for the adsorption of the pollutant.

ABSTRACT Many Amazonian farmers use the slash-and-burn method rather than fertilization for crop production. The aim of the present study was to evaluate changes in the morphological, physical, and chemical properties of naturally fertile Inceptisols after conversion from native forest to different uses in southern Amazonia, Brazil. Land covered by dense native forest (NF) was split into four areas of 1.0 ha each. Three areas were slashed and burned and then cultivated for 11 years with coffee (CO), secondary forest (SF), and pasture (PA). Four soil profiles were sampled in each treatment (four uses × four replicates). The mean value distribution of each physical and chemical analysis was determined for different depths, and standard error bars were placed to display significant differences among treatments. Results showed that morphology and physical properties were negatively affected after the establishment of PA and CO: a reduction in the thickness of the A horizon and in aggregate stability, a decrease in total porosity and macroporosity, and an increase in aggregate size and bulk density. Soil bulk density (SBD), geometric mean diameter of water-stable aggregates (GMD), and microporosity (SMi) were higher in soil under pasture as a consequence of more intense soil surface compaction. Native and secondary forests were the only treatments that showed granular structures in the A horizon. Significant differences between native forest and secondary forest were mainly found in the top soil layer for total porosity (STP) (NF>SF), macroporosity (SMa) (NF>SF), SBD (NF>SF) and GMD (SF>NF). Phosphorus contents in the A horizon increased from 6.2 to 21.5 mg kg-1 in PA and to 27.2 mg kg-1 in SF. Soil under coffee cultivation exhibited the lowest levels of Ca2+ and sum of bases in surface horizons. In all slash-and-burn areas there was a reduction in the C stock (Mg ha-1) of the A horizon: native forest 6.3, secondary forest 4.5, pasture 3.3, and coffee 3.1.

ABSTRACT Despite the considerable amount of information on the mineralogical characteristics of pedogenic Fe oxides in Brazilian soils, there are few studies on Fe-rich soils developed from mafic rocks with taxonomic identities at lower categorical levels. This study evaluated the mineralogical characteristics of pedogenic Fe oxides in B horizons (Bw) of Fe-rich Oxisols developed from several mafic rocks in the state of Minas Gerais, Brazil. The Bw horizons were sampled at a 0.8-1.0 m depth in 13 Ferric and Perferric Rhodic Oxisols along with a Mesoferric Typic Oxisol originating from basalt, gabbro, tuffite, amphibolite and itabirite in Minas Gerais. The selected soils have taxonomic identities up to the fourth categorical level of the Brazilian System of Soil Classification. In the laboratory, the following analyses were made: a) powder X ray diffraction (XRD) of the clay fraction before and after selective concentration of Fe oxides by silicate alkaline dissolution (5 mol L-1 NaOH); b) selective chemical dissolution of the clay fraction by citrate-bicarbonate-dithionite (CBD), acid ammonium oxalate (AAO), and sulfuric acid (H2SO4 1.8 mol L-1); c) quantitative estimation of minerals in the clay fraction through allocation of phases from the XRD patterns, magnetic susceptibility of the clay fraction, and quantification of elements after sulfuric acid digestion (H2SO4 1:1) of the air-dried fine earth and treatment of the clay fraction with CBD; and d) estimation of the mean crystal size (MCS), specific surface area (SSA), and isomorphic Al-substitution (IS) of hematite, goethite, and maghemite from the XRD patterns obtained from concentrates of Fe oxides. The results showed that estimation of Fe content of maghemite by selective dissolution with 1.8 mol L-1 H2SO4 may not be accurate enough to realistically reflect the maghemite contents in the soil sample. The Al content extracted may also be influenced by other minerals that are sources of this element. Hematite crystals were predominantly placoid in shape in all Rhodic Oxisols and had smaller SSA compared to goethite, which showed both isodimensional and asymmetric habit. Higher crystallinity of maghemite and the IS values generally lower than those of hematite and goethite suggest that in well-drained soils derived from mafic rocks, the IS phenomenon in maghemites seems to result from pedogenetic advancement after its formation from magnetite oxidation.

ABSTRACT: Extraction of K and Mg with boiling 1 mol L-1 HNO3 in an open system for predicting K and Mg uptake by plants is a method of low reproducibility. The aim of this study was to compare the extraction capacity of different acid methods relative to hydrofluoric acid extraction for K and Mg. A further objective was to develop a chemical extraction method using a closed system (microwave) for nonexchangeable and structural forms of these nutrients in order to replace the traditional method of extraction with boiling HNO3 on a hot plate (open system). The EPA 3051A method can be used to estimate the total content of K in the clay fraction of soils developed from carbonate and phyllite/mica schist rocks. In the clay fraction of soils developed from basalt, recoveries of K by the EPA 3051A (pseudo-total) method were higher than for the EPA 3052 (total hydrofluoric extraction) method. The relative abundance of K and Mg for soils in carbonate rocks, phyllite/mica schist, granite/gneiss, and basalt determined by aqua regia digestion is unreliable. The method using 1 mol L-1 HNO3 in an closed system (microwave) showed potential for replacing the classical method of extraction of nonexchangeable forms of K (boiling 1 mol L-1 HNO3 in an open system - hot plate) and reduced the loss of Si by volatilization.

RESUMO A interação de compostos orgânicos com minerais de argila pode alterar o tamanho dos cristais. No entanto, em solos, esse efeito é ainda pouco claro por causa das limitações na separação de fases puras de minerais para realizar experimentos de dissolução. Neste estudo, a relação entre a matéria orgânica do solo (MOS) e diâmetro médio do cristal (DMC) de minerais de argila de horizontes superficiais e subsuperfíciais de solos de uma topossequência no sul do Brasil foi avaliada. Os teores de C e N foram determinados, e a natureza dos grupos funcionais da MOS foi avaliada por espectroscopia de FTIR. O DMC dos minerais foi avaliado por difração de raios X, em umas amostras desferrificadas e outras com óxidos de Fe concentrados. Os teores de C e N e as intensidades relativas dos espectros de FTIR foram considerados como variáveis preditoras; e o DMC de hematita, goethita, caulinita e gibbsita, como variáveis preditas. Os teores de C e N e os grupos carboxílicos e C-O-Alquil evidenciaram efeito significativo sobre a variação do DMC. A dimensão dos cristais de óxidos de Fe e de caulinita foi inversamente correlacionada com esses atributos da MOS. Em contraste, o DMC de gibbsita não foi influenciado pelos atributos dae MOS. A influência da MOS sobre o DMC dos óxidos de Fe foi atribuída às reações de complexação de superfície e de redox, que promovem um processo contínuo de dissolução-precipitação.

ABSTRACT The interaction of organic compounds with clay minerals can change the size of crystals. However, in soils this effect is still unclear because of limitations in separation of pure mineral phases for conducting dissolution experiments. In this study, the relationship between soil organic matter (SOM) and mean crystallite size (MCS) of clay minerals from surface and subsurface horizons of soils from a toposequence in Southern Brazil was evaluated. Soil C and N contents were determined and the nature of the SOM functional groups were evaluated by FTIR spectroscopy. The MCS of minerals was assessed by X ray diffraction performed on Fe-oxide free samples and on Fe-concentrated samples. The C and N content and the relative intensities of the FTIR spectra were considered as predictor variables, and the MCS of hematite, goethite, kaolinite, and gibbsite as predicated variables. The C and N content and carboxylic and C-O-alkyl groups showed significant effects on the variation of MCS. The crystallite dimension of the Fe-oxides and kaolinite was inversely affected by these SOM properties. In contrast, the MCS of gibbsite was not affected by the SOM properties. The SOM influence on the MCS of Fe-oxides was attributed to surface complexation reactions and to surface redox reactions that promote a continuous dissolution-precipitation process.