Phosphate sorption and desorption by two contrasting volcanic soils of equatorial Africa

Volcanic soils cover 1% of the Earth's surface but support 10% of the world's population. They are among the most fertile soils in the world, due to their excellent physical properties and richness in available nutrients. The major limiting factor for plant growth in volcanic soils is phosphate fixation, which is mainly attributable to active species of aluminium and iron. The sorption and desorption of phosphate is studied on the surface horizons of two African agricultural soils, a silandic Andosol (Rwanda) and a vitric Andosol (São Tomé and Principe). Both soils are slightly acid. The silandic Andosol is rich in active aluminium forms, while the vitric Andosol has high amounts of crystalline iron and aluminium oxides. Sorption isotherms were determined by equilibrating at 293K soil samples with phosphate solutions of concentrations between 0 and 100 mg P L-1 in NaNO3; phosphate was determined by visible spectrophotometry in the equilibrium solution. To study desorption, the soil samples from the sorption experiment were equilibrated with 0.02 M NaNO3. The isotherms were adjusted to mathematical models. In almost all the concentration range, the adsorption of phosphate by the silandic Andosol was greater than 90% of the amount added, being lower in the vitric Andosol but always higher than 65%. The high sorption by the silandic Andosol is attributed to its richness in non-crystalline Fe and Al, while in the vitric Andosol crystalline iron species seem to play a relevant role in the adsorption. The sorption isotherms of both soils fitted to the Temkin model, the adjustment to the Langmuir or Freundlich models being unsatisfactory; throughout the range studied, the sorption increases with increasing phosphorus concentration, a maximum sorption is not predictable (as occurs when the sorption is adjusted to the Langmuir model). For an added P concentration of 100 mg L-1 (3.2 mmol L-1), the sorption is 47.7 mmol P g-1 in the silandic Andosol and 41.6 mmol P g-1 in the vitric Andosol. The desorption is low and the comparison of the sorption and desorption isotherms reveals a pronounced hysteresis, that is, the irreversibility of the sorption. The high phosphate sorption and its irreversibility are comparable to those published for other volcanic soils with high contents of allophane, active aluminium and free iron. The strong phosphate adsorption is a serious limiting factor for plant growth, which requires a careful management of phosphorus fertilization.S

Sorption and Desorption of Vanadate, Arsenate and Chromate by Two Volcanic Soils of Equatorial Africa

Sorption of oxyanions by soils and mineral surfaces is of interest due to their role as nutrients or pollutants. Volcanic soils are variable charge soils, rich in active forms of aluminum and iron, and capable of sorbing anions. Sorption and desorption of vanadate, arsenate, and chromate by two African andosols was studied in laboratory experiments. Sorption isotherms were determined by equilibrating at 293 K soil samples with oxyanion solutions of concentrations between 0 and 100 mg L−1 V, As, or Cr, equivalent to 0−2.0 mmol V L−1, 0−1.3 mmol As L−1, and 0−1.9 mmol Cr L−1, in NaNO3; V, As, or Cr were determined by ICP-mass spectrometry in the equilibrium solution. After sorption, the soil samples were equilibrated with 0.02 M NaNO3 to study desorption. The isotherms were adjusted to mathematical models. After desorption with NaNO3, desorption experiments were carried out with a 1 mM phosphate. The sorption of vanadate and arsenate was greater than 90% of the amount added, while the chromate sorption was much lower (19–97%). The sorption by the Silandic Andosol is attributed to non-crystalline Fe and Al, while in the Vitric Andosol, crystalline iron species play a relevant role. The V and Cr sorption isotherms fitted to the Freundlich model, while the As sorption isotherms conformed to the Temkin model. For the highest concentrations of oxyanions in the equilibrating solution, the sorbed concentrations were 37–38 mmol V kg−1, 25 mmol As kg−1, and 7.2–8.8 mmol Cr kg−1. The desorption was low for V and As and high for Cr. The comparison of the sorption and desorption isotherms reveals a pronounced hysteresis for V in both andosols and for Cr in the Silandic Andosol. Phosphate induced almost no V desorption, moderate As desorption, and considerable Cr desorptionS

Neoformacion de minerales de la arcilla en la Espana Peninsular: tendencias termodinamicas basadas en la composicion de las aguas de los rios españoles

Stable or metastabie minerals are established for 381 sampling points from river water compositions for every spanish watershed aiong the years 1974-75, 1975-76, 1981-82, 1982-83 and 1983-84, as published by the spanish Department of Public Works. Phase diagrams for the systems SiO2-Al2O3-H2O, K2O-SiO2-Al2O3-H2O, Na2O-SiO2-Al2O3-H2O, MgO-SiO2-Al2O3-H2O, and CaO-SiO2-Al2O3-H2O, for 298 K and 1 atm. conditions, are used in order to determine the mineraiogical stability, and therefore neoformation trends. Stable and metastable phases were taken into account to draw the diagrams (Fernandez Marcos and Macias, 1987). The prevailing trend in the Peninsula, according to this method, is towards kaolinite neoformation. Nevertheless differences are observed between watersheds. So kaolinite is the only stable mineral neoformed in the North watersheds while there exist severa! stable minerals (kaolinite, mica, (kaolinite, mica, chlorite, pyrophillite) or metastable ones (smectite) in the Tajo, Guadiana, Guadalquivir, South, Jucar, Segura and East Pyrenees watersheds, depending on sampling point and date. Geographic distribution of different minerals is satisfactorily explained by taking into account: rainfall distribution, sileceous or calcareous nature of ground, and upper, medium or lower position in the river course

A contribution to the study of the stability of clay minerals from the soil solution composition at different pF values

(EN)The composition of the soil solution of various horizons of Galician soils was studied to gain insight into the direction of the processes of weathering and neoformation by means of stability diagrams of the clay minerals. The soil solution was extracted by compression at various pF values. The most significant results are as follows: In all the cases studied the mineral in equilibrium with the soil solution is a 1:1 phyllosilicate. As the pF at which the soil solution is extracted increases, corresponding to smaller pore size, pH increases and silica concentration falls. The stable mineral does not vary significantly between different horizons of the same profile. Each parent material gives rise to a different zonation in the stability diagrams. The predictions of the stability diagrams are in general agreement with the mineralogical data of the clays of the horizons in question. Finally, weathering processes in Galicia are briefly commented on.(ES)Se realiza un estudio de la composición de la solución del suelo extraída por compresión a diferentes valores de pF como medio de conocer la dirección de los procesos de alteración y neoformación en diversos horizontes de suelos de Galicia, utilizando diagramas de estabilidad de los minerales de la arcilla. Los resultados más significativos son los siguientes: En todos los casos estudiados el mineral en equilibrio con la solución del suelo es un filosilicato 1:1. La solución extraída a valores crecientes de pF, que corresponden a tamaños de poros más pequeños, presenta valores de pH más altos y disminución de la concentración de sílice. No se aprecian diferencias significativas en cuanto al mineral estable en los diferentes horizontes de un mismo perfil. Para cada material original se aprecia una diferente zonaci6n en los diagramas de estabilidad. Las predicciones de los diagramas de estabilidad están generalmente de acuerdo con los datos mineralógicos de las arcillas de los horizontes correspondientes. Finalmente se realizan unas breves consideraciones sobre los procesos de alteración en Galicia

Potentially Toxic Elements in Urban Soils of Havana, Cuba

Urban soils are characterised by a strong anthropogenic influence. Potentially toxic elements were studied in various horizons of 35 urban soils in Havana, Cuba, classified as Urbic or Garbic Technosols. Pseudo-total, available, and acid-oxalate extractable concentrations were determined. The pseudo-total concentrations were generally higher than the average values for the world’s soils but similar to those published for urban soils. In a few cases, very high values of copper or lead were found. Nickel and chromium concentrations exceeded the maximum allowable concentrations for agricultural soils in 22% and 12% of samples. Vanadium concentrations were always very high. There was minimum enrichment of most samples in Co, Mn, As, Cd, Cr, Cu, and Ni, but outliers reached moderate or significant enrichment. Enrichment was significant for V, while for Pb, Zn, and Hg the median values denoted moderate enrichment, but outliers reached significant enrichment in Zn and extremely high enrichment in Pb and Hg. The available elements amounted to between 0.07% of the pseudo-total vanadium and 30% lead and cadmium. The published toxicity limits for bioavailable Cd, Mn, Ni, and Pb were exceeded in 14%, 39%, 10%, and 56% of samples, respectively. The concentrations of pseudo-total total iron, cobalt, chromium, and nickel, and available cobalt, nickel and titanium were significantly lower in soils with gleyic properties (reducing conditions)S

Nitrogen, phosphorus, potassium, calcium and magnesium releasefrom two compressed fertilizers: column experiments

The objective of this work was to study nutrients release from two compressed nitrogen–potassium–phosphorous (NPK) fertilizers. In the Lourizán Forest Center, tablet-type controlled-release fertilizers (CRF) were prepared by compressing various mixtures of fertilizers without covers or binders. We used soil columns (50 cm long and 7.3 cm inner diameter) that were filled with soil from the surface layer (0–20 cm) of an A horizon corresponding to a Cambic Umbrisol. Tablets of two slow-release NPK fertilizers (11–18–11 or 8–8–16) were placed into the soil (within the first 3 cm), and then water was percolated through the columns in a saturated regime for 80 days. Percolates were analyzed for N, P, K+, Ca2+ and Mg2+. These elements were also determined in soil and fertilizer tablets at the end of the trials. Nutrient concentrations were high in the first leachates and reached a steady state when 1426 mm of water had been percolated, which is equivalent to approximately 1.5 years of rainfall in this geographic area. In the whole trial, both tablets lost more than 80% of their initial N, P and K contents. However, K+, Ca2+ and Mg2+ were the most leached, whereas N and P were lost in leachates to a lesser extent. Nutrient release was slower from the tablet with a composition of 8–8–16 than from the 11–18–11 fertilizer. In view of that, the 8–8–16 tablet can be considered more adequate for crops with a nutrient demand sustained over time. At the end of the trial, the effects of these fertilizers on soil chemical parameters were still evident, with a significant increase of pH, available Ca2+, Mg2+, K+, P and effective cation exchange capacity (eCEC) in the fertilized columns, as well as a significant decrease in exchangeable Al3+, reaching values < 0.08 cmol (+) kg−1.S

Efeito do tamanho das partículas de calcário nos teores de Ca, Mg e K no solo e em plantas forrageiras

Liming increases crop production through improved soil conditions in acidic soils. Among the effects of liming, increased availabilities of alkaline and alkaline-earth cations are worth mention. These availabilities may be affected by the particle size of applied limestone, which influences lime reactivity. The effects of particle size and application schedule of magnesium limestone were investigated on extractable Ca, Mg and K in soil, their concentrations in sward plants and dry-matter yield. Magnesium limestone of various particle sizes was applied to experimental plots at a rate of 3 t ha-1, a grass-clover sward was sown, and the plots were monitored during three years. The finest limestone (< 0.25 mm) in a single application yielded the highest soil Ca and Mg concentrations extracted by Mehlich-3 and NH4Cl. The same limestone split in three annual doses was less effective. Plots treated with the coarsest limestone (2-4 mm) did not differ from control plots. Liming had no effect on potassium, either in soil or plants. Soil concentrations of Ca, Mg and K extracted by Mehlich-3 and NH4Cl were correlated with each other (r = 0.76, 0.75 and 0.67, respectively). NH4Cl extracted more Ca than Mehlich-3, while the latter extracted more Mg and K than NH4Cl. Soil Ca, Mg and K extracted by NH4Cl were also correlated to water extractions. Mg concentration in plants correlated to soil Mg extracted by NH4Cl or by water. Neither the concentrations nor the total contents of Ca and K in plants correlated with extractable soil Ca and K. The total dry matter yield was not affected by liming. The yield of sown species was higher in plots treated with the finest limestone than in plots limed with the coarsest limestone. Cations extracted by water or NH4Cl explained the variance of dry matter yield.A aplicação de calcário em solos ácidos promove aumento da produção agrícola por meio da melhoria das condições do solo. Entre os efeitos da calagem, o aumento da disponibilidade de cátions alcalinos e alcalino-terrosos são dignos de menção. Essas disponibilidades podem ser afetadas pelo tamanho das partículas do calcário aplicado, que influencia a solubilidade do mesmo. Investigaram-se os efeitos da granulometria e épocas de aplicação de calcário magnesiano nos cátions trocáveis Ca, Mg e K extraidos no solo, nas suas concentrações em plantas crescidas cultivadas nesse solo e no rendimento das suas matérias secas. Vários tamanhos de partículas de calcário magnesiano foram aplicadas às parcelas experimentais, a uma taxa de 3 t ha-1, gramíneas e trevo foram plantados e as parcelas foram monitoradas durante três anos. O calcário mais fino (< 0,25 mm) em uma única aplicação proporcionou os maiores teores de Ca e Mg extraídos por Mehlich-3 e por NH4Cl. Este mesmo calcário quando aplicado parcelado em três doses anuais foi menos eficaz. Parcelas tratadas com o clacário mais grosseiro (2-4 mm) não diferiram da testemunha. A calagem não teve efeito sobre o potássio, quer seja no solo ou nas plantas. As concentrações no solo de Ca, Mg e K extraídos por Mehlich-3 e NH4Cl foram positivamente correlacionadas. O NH4Cl extraiu mais Ca do que o Mehlich-3, enquanto o segundo extraíu mais Mg e K do que o NH4Cl. O Ca, Mg e K extraídos pelo NH4Cl foram também correlacionados com extrações por água. Concentrações de Mg em plantas estão relacionadas com concentrações de Mg no solo extraídos pelo NH4Cl ou pela água. Nem as concentrações ou teores totais de Ca e K nas plantas correlacionaram-se com as concentrações extraídas de Ca e K do solo. O rendimento de matéria seca total não foi afetado pela calagem. A produtividade das espécies cultivadas foi maior nas parcelas tratadas com os calcários mais finos do que em parcelas com calcário mais grosseiro. Cátions extraídos pela água ou NH4Cl correlacionaram-se com a variação da produção de matéria seca.This research was supported by autonomous Government of GalicianS

Validation of microRNA expression profile in Oral Lichenoid Disease through cytological samples

To validate oral exfoliative cytology in the analysis of the microRNA expression profile in Oral Lichenoid Disease (OLD). The expression of 13 microRNAs identified and presented by our group in a previous study was analyzed in 26 cases, 16 diagnosed as OLD and 10 controls with no oral mucosal pathology. Cytological samples from the oral mucosa obtained using an Orcellex toothbrush were analyzed using RT-qPCR and TaqMan microRNA assays. The aberrant expression was validated for 2 microRNAs (miR-146a-5p and miR-7-1-3p) of those previously recognized in the biopsy study. This is the first time that oral exfoliative cytology is validated in a study of the alterations of the expression of microRNAs in OLD. The alteration of miR-146a and miR-7 compared to controls was validated. These microRNAs are associated with both inflammatory and carcinogenic phenomena that are involved in the etiopathogenesis of this potentially malignant oral disorder

Complejidad en el paciente frágil joven: dificultad para la asistencia y la atención

A 63-year-old patient with multiple myeloma with chronic renal failure and myasthenia gravis who has acute respiratory infection. Unfavorable evolution is observed by associating with acute hepatitis of drug origin. After a comprehensive assessment of the patient, the finding of possible fronto-temporal dementia is previously masked as a depressive disorder. The use of drugs in this patient implies relevant conditioning, so a therapeutic reconciliation must be carried out to avoid complications related to comorbidities.Paciente de 63 años con mieloma múltiple, insuficiencia renal crónica y miastenia gravis que presentaba infección respiratoria aguda. Se objetivó la evolución desfavorable, asociándose con hepatitis aguda de origen medicamentoso. Tras valoración integral del paciente, se llegó al hallazgo de posible demencia frontotemporal, enmascarada de forma previa como trastorno depresivo. La utilización de fármacos en esta paciente implica condicionamientos relevantes, por lo que se debe realizar una conciliación para evitar complicacio- nes relacionadas con las comorbilidades

Assessment of Potential Nutrient Release from Phosphate Rock and Dolostone for Application in Acid Soils

This is the accepted manuscript of the following article: Rafael, R. B. A., Fernández-Marcos, M. L., Cocco, S., Ruello, M. L., Weindorf, D. C., Cardelli, V., and Corti, G. (2018). Assessment of Potential Nutrient Release from Phosphate Rock and Dolostone for Application in Acid Soils. Pedosphere 28, 44-58. doi: 10.1016/S1002- 0160(17)60437-5Finding alternative local sources of plant nutrients is a practical, low-cost, and long-term strategy. In this study, laboratory column experiments were conducted in a completely randomized design to evaluate the feasibility of using phosphate rock and dolostone as fertilizers or acid-neutralizing agents for application in tropical acid soils. The dissolution rates of different particle-size fractions (0.063–0.25, 0.25–0.5, and 0.5–2 mm) of both rocks were studied by citric acid solution at pH 4 and 2 and water, with extraction times of 1, 3, 5, 7, 12, 24, 72, 144, 240, and 360 h. The results showed that the dissolution of both rocks depended on the particle size, leaching solution, and extraction time. The dissolution rate of rock-forming minerals increased as the specific surface area increased, corresponding to a decrease in particle size. In all cases, the release kinetics was characterized by two phases: 1) a first stage of rapid release that lasted 24 h and would ensure short-term nutrient release, and 2) a second stage of slow release after 24 h, representing the long-term nutrient release efficiency. Both rocks were suitable as slow-release fertilizers in strongly acid soils and would ensure the replenishment of P, Ca, and Mg. A combination of fine and medium particle-size fractions should be used to ensure high nutrient-release efficiency. Much work could remain to determine the overall impact of considerable amounts of fresh rocks in soilsThis study was mainly supported by the “Applied Research and Multi-sectorial Program” (FIAM) (No. 5.2.1) granted by the Italian Cooperation and Development Agency (ICDA) to the Universidade Eduardo Mondlane. The authors also acknowledge the Polytechnic University of Marche, Italy for the PhD scholarship provided to the first author as well as research funding for this workS