Boron adsorption in acric soils as a function of pH variation

A adsorção de B pelo solo é o principal fenômeno que afeta sua disponibilidade e seu potencial de contaminação. Os objetivos deste estudo foram: (a) investigar os efeitos do pH na adsorção de B em amostras superficiais e subsuperficiais de um Latossolo Vermelho Acriférrico (LVwf) e de um Latossolo Amarelo Ácrico (LAw) - ambos com balanço positivo de cargas no horizonte Bw - e de um Nitossolo Vermelho eutroférrico (NVef); (b) avaliar a adequação do modelo de Langmuir em simular os resultados experimentais de adsorção; e (c) correlacionar os atributos químicos, físicos e mineralógicos dos solos com os valores de adsorção máxima (Ads máx) e do coeficiente de afinidade (K L), derivados das isotermas. Experimentos do tipo batch foram realizados para determinação da quantidade de boro adsorvido, tendo como eletrólito-suporte soluções de NaCl 0,01 mol L-1 com 0,1; 0,2; 0,4; 0,8; 1,2; 1,6; 2,0; e 4,0 µg mL-1 de B. Houve aumento da adsorção de B com a elevação do pH e da concentração inicial de B adicionado. Maiores quantidades de B foram adsorvidas na amostra superficial do NVef e nos horizontes Bw positivamente carregados dos Latossolos ácricos. A adsorção de B foi representada por isotermas dos tipos C (linear) e L (exponencial) e adequadamente ajustada pelo modelo de Langmuir. Os parâmetros Ads máx e K L estimados por regressão não-linear não se correlacionaram com o pH. No pH natural, teores de matéria orgânica (MO) e de argila foram as variáveis que mais influenciaram a Ads máx nas camadas superficiais. Nas camadas subsuperficiais, a Ads máx correlacionou-se negativamente com os teores de MO e positivamente com os de gibbsita. Teores de (hidr)óxidos de Fe cristalinos e amorfos estiveram correlacionados aos valores de K L obtidos nas amostras subsuperficiais e ao pH natural, bem como à Ads máx das camadas superficiais após aumento do pH.Boron (B) adsorption by soils affects its bioavailable contents and contamination potential. The objectives of this study were: (a) to investigate the effects of pH variation on B adsorption by topsoil and subsoil samples from an Anionic Rhodic Acrudox (RA), an Anionic Xanthic Acrudox (XA) - both with a positive balance of charge in Bw horizon - and a Rhodic Kandiudalf (RK); (b) to evaluate the ability of the Langmuir model of simulating the experimental results of B adsorption; and (c) to correlate chemical, physical and mineralogical soil attributes with the values of maximum adsorption (Ads max) and affinity coefficient (K L), derived from the isotherms. To quantify the amount of adsorbed B, batch experiments were carried out using a 0.01 mol L-1 NaCl solution as a support electrolyte containing 0.1; 0.2; 0.4; 0.8; 1.2; 1.6; 2.0 and 4.0 µg mL-1 of B. An increase of B adsorption was observed after raising the pH (between 3.5 and 8.0) and the initial concentration of added B. Larger amounts of B were adsorbed in topsoil samples from RK and in Bw positively charged horizons from acric Oxisols. Boron adsorption was represented by type-C (linear) and type-L (exponential) isotherms and well fitted by the Langmuir model. Ads max and K L, estimated by nonlinear regressions, were not correlated with the pH. At a natural pH, the organic matter (OM) and clay contents influenced Ads max most in the topsoil samples. In the subsoil layers, Ads max was negatively correlated with OM contents and positively correlated with gibbsite contents. At a natural pH, the contents of free and amorphous Fe (hydr)oxides were correlated with K L values from subsoil samples. After pH increase, the oxide contents were correlated with Ads max values from the topsoil samples.FAPES

Curvaturas de relevo, mineralogia da argila e adsorção de fósforo em Argissolo cultivado com cana-de-açúcar

As curvaturas do relevo promovem pedoambientes específicos que condicionam os atributos químicos e mineralógicos do solo e podem auxiliar na definição de zonas específicas de manejo. O fósforo (P) é um dos principais elementos limitantes ao desenvolvimento e longevidade do canavial. O teor e a constituição mineralógica da fração argila assumem papel importante na disponibilidade do P, sendo que a gibbsita (Gb), quando presente em altas proporções no solo, pode ser a principal responsável pela sua adsorção e indisponibilidade. Investigaram-se as relações e a variabilidade espacial da adsorção de P e a ocorrência de caulinita (Ct) e gibbsita na fração argila de um Argissolo Vermelho-Amarelo eutrófico originado de rochas areníticas sob diferentes curvaturas do relevo em área sob cultivo de cana-de-açúcar. Duas malhas de 1 ha foram delimitadas numa área côncava e outra área convexa. Foram coletadas 121 amostras em cada área para realização das análises granulométricas, químicas e mineralógicas. A capacidade máxima de adsorção de P foi obtida em seis amostras escolhidas ao acaso em cada área. Os resultados foram submetidos às análises estatísticas descritiva e geoestatística. Os menores valores médios de P disponível encontraram-se na área convexa. Nesta área, a proporção de gibbsita, expressa pelos valores da razão [Gb/(Gb+Ct)] e os valores de capacidade máxima de adsorção de fósforo foram maiores do que na área côncava.Hillslope curvatures are associated with specific environments that correlate to chemical and mineralogical attributes of soil, so determining specific management zones. Phosphorus is one of the main limiting factors to the development and longevity of sugarcane. The type and the mineralogical constitution of the clay fraction play an important role in the phosphorus (P) adsorption of soil. High proportion of gibbsite (Gb) in soil may be the major responsible for P adsorption. The relationships among spatial variability as a function of hillslope curvature, the proportion of kaolinite (Kt) and Gb, and phosphorus adsorption were evaluated in an Alfisol cultivated with sugarcane. Two plots of 1 ha of a concave and a convex hillslope area were selected and 121 samples were collected in each area. The maximum P adsorption was determined in six samples taken randomly in each area. Data were submitted to descriptive statistical and geostatistical analysis. The lowest average values of available phosphorus were found in the convex area. In this area, the proportion of gibbsite, expressed by the values of the ratio [Gb/(Gb + Ct)] and the values of maximum adsorption capacity of phosphorus were higher than in the concave area

Electrochemical attributes of acric soils from the North of São Paulo State

Extensas áreas ao norte do estado de São Paulo assentam-se sobre solos ácricos. que localizam-se no extremo da escala de intemperismo, possuindo bons atributos físicos. por serem normalmente profundos e friáveis mas apresentando, por definição, baixíssima capacidade de troca de cátions efetiva (menor que 1.5meq / 100g de argila). Estas áreas são utilizadas para cultivo de culturas irrigadas, como feijão e trigo, e outras culturas, como a soja e a cana-de-açúcar, todas elas altamente tecnificadas. Este estudo foi conduzido com objetivo de quantificar os atributos eletroquímicos de alguns solos ácricos e comparálos com os de outros solos menos intemperizados. Foram usadas amostras superficiais e subsuperficiais de latossolos roxos ácricos e latossolos variação Una ácricos das cidades de Ribeirão Preto, Guaíra e Miguelópolis, a Terra Roxa Estruturada (localizada em Ribeirão Preto) e o Latossolo Roxo eutrófico (Campinas. Além das análises químicas e físicas de rotina, foi determinado o ponto de efeito salino nulo (PESN), através de curvas de titulação potenciométrica. Foi feita também a caracterização mineralógica com difração de raio-X e análise térmica diferencial, e f'oram calculados o potencial elétrico e a carga elétrica superficial. Aplicaram-se os modelos da dupla camada difusa de Gouy-Chapman e de Stern, a fim de se observar a relação entre os dados obtidos e estes modelos teóricos. O caráter ácrico apareceu a diferentes profundidades, sendo que no Latossolo variação Una argilo-arenoso, de coloração mais amarelada, ele se manifestou a apenas 50cm da superfície. A mineralogia dos solos foi essencialmente caulinítica e sesquioxídica, indicando o estágio avançado de intemperismo destes solos. Como era de se esperar, a retenção de cátions foi baixa, sendo que em algumas amostras a soma de bases foi inferior a 0.3 meq/100g de terra. Apenas no Latossolo variação Una ácrico muito argiloso a saturação por alumínio foi alta (maior que 50%), sendo que nas demais ela foi praticamente nula. A matéria orgânica da camada superficial influenciou significativamente o PESN, que esteve em torno de 3.5 para todas as amostras estudadas. Na TE não houve variação do PESN em subsuperfície. Em todos os latossolos, o PESN aumentou em profundidade. indicando menor efeito da matéria orgânica e maior participação dos óxidos de ferro e a1umínio na definição das cargas. Os latossolos roxos ácricos e o latossolo variação Una argi1o-arenoso apresentaram balanço positivo de carga em profundidade. Nestes solos o ΔpH foi positivo, ou seja, o pH medido em KCI 1N foi superior ao pH medido em H2O. O Latossolo Roxo eutrófico teve um Δ pH igual a zero e as demais amostras um Δ pH negativo, indicando nestas camadas predomínio das cargas negativas sobre as positivas. O PESN correlacionou-se positivamente com teor de gibbsita e negativamente com o indice ki dos solos. Os valores de superfície específica foram baixos (média de 37 m2/g) e, tal vez por isso, os valores de carga líquida ajustaram-se melhor ao modelo de Gouy-Chapman do que ao modelo de Stern.Large areas of soi1s composed by acric materials are found in the North of São Paulo State. These highly weathered soi1s have good physica1 conditions, due to their high depth and friability, but are chemica11y poor having, by definition, an effective cation exchange capacity 1ower than 1,5cmol(+) / kg c1ay. In that areas, many irrigated Crops are grown, as beans and wheat, and other non-irrigated crops as soybean and sugarcane, a11 cultivated with high technology. This study was carried out. In order to quantify the e1ectrochemica1 attributes of some acric soi1s and compare them with those of less weathered soils. Surface and subsurface samp1es of four acric Oxiso1s from Ribeirão Preto, Migue1ópo1is and Guaíra (named Dusky-Red Latosol and Una variant Latosol), State of São Paulo, were studied with two other soi1s: an Oxiso1 (Dusky-Red Latosol) from Campinas and A1fiso1) "Terra Roxa Estruturada") f'rom Ribeirão Preto, both without acric attributes. Besides the routine chemical and physical analysis, qualitative and quantitative mineralogical attributes were determined and the resu1ts of X-ray diffractions and differential thermal analysis showed that the clay fractions contained mainly iron oxides, gibbsite and kao1inite. Net electric charge was determined by potenciometric titration of the soi1 samp1es in the presence of varying concentration of KCl. The titration curves, at three different ionic strengths of KCl, crossed at a common point, the zero point of salt effect (ZPSE), or the pH at which the net e1etric charge was zero. Net surface charge density was found to vary with pH and electrolyte concentration. A theoretical study of the values for the net charge was made by the application of the double layer theory of Gouy-Chapman and Stern. The experimental values were in better agreement with the Gouy-Chapman theory, maybe because of the low va1ues of surface area (mean of 37m2/g). The acric character was present at different depths, for instance 50cm in the clayey marginal to medium textured Una variant Latosol, with brownish color. The cation retention was very low, and in some samples the sum of bases was lower than (0.3cmol(+) / kg of soi1. In only one sample (clayey Una variant Latosol) the aluminum percentage was high, more than 50%. Organic matter had strong influence in the ZPSE values of the surface layers, because they were around 3,5 in all samples. In the Alfisol, there was no change in the subsurface ZPSE value, but in all Oxisol samples studied the ZPSE had increased very much, showing the biggest participation of the oxides in the charge balance of B horizon. The acric Dusky-Red Lalosols from Ribeirão Preto and Guaíra and the medium textured Una variant Latosol from Guaíra exhibited positive balance of charge in subsurface, because the ΔpH was positive or, in other words, the pH measured in KCl 1N was higher than the pH measured in water. The Dusky-Red latosol (not acric) from Campinas had a ΔpH equal to zero and the other samples a negative ΔpH, indicating a predominance of negative over positive charges. The ZPSE had positive correlation with the gibbsite amount and negative correlation with the ki index

Electrochemical attributes of acric soils from the North of São Paulo State

Extensas áreas ao norte do estado de São Paulo assentam-se sobre solos ácricos. que localizam-se no extremo da escala de intemperismo, possuindo bons atributos físicos. por serem normalmente profundos e friáveis mas apresentando, por definição, baixíssima capacidade de troca de cátions efetiva (menor que 1.5meq / 100g de argila). Estas áreas são utilizadas para cultivo de culturas irrigadas, como feijão e trigo, e outras culturas, como a soja e a cana-de-açúcar, todas elas altamente tecnificadas. Este estudo foi conduzido com objetivo de quantificar os atributos eletroquímicos de alguns solos ácricos e comparálos com os de outros solos menos intemperizados. Foram usadas amostras superficiais e subsuperficiais de latossolos roxos ácricos e latossolos variação Una ácricos das cidades de Ribeirão Preto, Guaíra e Miguelópolis, a Terra Roxa Estruturada (localizada em Ribeirão Preto) e o Latossolo Roxo eutrófico (Campinas. Além das análises químicas e físicas de rotina, foi determinado o ponto de efeito salino nulo (PESN), através de curvas de titulação potenciométrica. Foi feita também a caracterização mineralógica com difração de raio-X e análise térmica diferencial, e f'oram calculados o potencial elétrico e a carga elétrica superficial. Aplicaram-se os modelos da dupla camada difusa de Gouy-Chapman e de Stern, a fim de se observar a relação entre os dados obtidos e estes modelos teóricos. O caráter ácrico apareceu a diferentes profundidades, sendo que no Latossolo variação Una argilo-arenoso, de coloração mais amarelada, ele se manifestou a apenas 50cm da superfície. A mineralogia dos solos foi essencialmente caulinítica e sesquioxídica, indicando o estágio avançado de intemperismo destes solos. Como era de se esperar, a retenção de cátions foi baixa, sendo que em algumas amostras a soma de bases foi inferior a 0.3 meq/100g de terra. Apenas no Latossolo variação Una ácrico muito argiloso a saturação por alumínio foi alta (maior que 50%), sendo que nas demais ela foi praticamente nula. A matéria orgânica da camada superficial influenciou significativamente o PESN, que esteve em torno de 3.5 para todas as amostras estudadas. Na TE não houve variação do PESN em subsuperfície. Em todos os latossolos, o PESN aumentou em profundidade. indicando menor efeito da matéria orgânica e maior participação dos óxidos de ferro e a1umínio na definição das cargas. Os latossolos roxos ácricos e o latossolo variação Una argi1o-arenoso apresentaram balanço positivo de carga em profundidade. Nestes solos o ΔpH foi positivo, ou seja, o pH medido em KCI 1N foi superior ao pH medido em H2O. O Latossolo Roxo eutrófico teve um Δ pH igual a zero e as demais amostras um Δ pH negativo, indicando nestas camadas predomínio das cargas negativas sobre as positivas. O PESN correlacionou-se positivamente com teor de gibbsita e negativamente com o indice ki dos solos. Os valores de superfície específica foram baixos (média de 37 m2/g) e, tal vez por isso, os valores de carga líquida ajustaram-se melhor ao modelo de Gouy-Chapman do que ao modelo de Stern.Large areas of soi1s composed by acric materials are found in the North of São Paulo State. These highly weathered soi1s have good physica1 conditions, due to their high depth and friability, but are chemica11y poor having, by definition, an effective cation exchange capacity 1ower than 1,5cmol(+) / kg c1ay. In that areas, many irrigated Crops are grown, as beans and wheat, and other non-irrigated crops as soybean and sugarcane, a11 cultivated with high technology. This study was carried out. In order to quantify the e1ectrochemica1 attributes of some acric soi1s and compare them with those of less weathered soils. Surface and subsurface samp1es of four acric Oxiso1s from Ribeirão Preto, Migue1ópo1is and Guaíra (named Dusky-Red Latosol and Una variant Latosol), State of São Paulo, were studied with two other soi1s: an Oxiso1 (Dusky-Red Latosol) from Campinas and A1fiso1) "Terra Roxa Estruturada") f'rom Ribeirão Preto, both without acric attributes. Besides the routine chemical and physical analysis, qualitative and quantitative mineralogical attributes were determined and the resu1ts of X-ray diffractions and differential thermal analysis showed that the clay fractions contained mainly iron oxides, gibbsite and kao1inite. Net electric charge was determined by potenciometric titration of the soi1 samp1es in the presence of varying concentration of KCl. The titration curves, at three different ionic strengths of KCl, crossed at a common point, the zero point of salt effect (ZPSE), or the pH at which the net e1etric charge was zero. Net surface charge density was found to vary with pH and electrolyte concentration. A theoretical study of the values for the net charge was made by the application of the double layer theory of Gouy-Chapman and Stern. The experimental values were in better agreement with the Gouy-Chapman theory, maybe because of the low va1ues of surface area (mean of 37m2/g). The acric character was present at different depths, for instance 50cm in the clayey marginal to medium textured Una variant Latosol, with brownish color. The cation retention was very low, and in some samples the sum of bases was lower than (0.3cmol(+) / kg of soi1. In only one sample (clayey Una variant Latosol) the aluminum percentage was high, more than 50%. Organic matter had strong influence in the ZPSE values of the surface layers, because they were around 3,5 in all samples. In the Alfisol, there was no change in the subsurface ZPSE value, but in all Oxisol samples studied the ZPSE had increased very much, showing the biggest participation of the oxides in the charge balance of B horizon. The acric Dusky-Red Lalosols from Ribeirão Preto and Guaíra and the medium textured Una variant Latosol from Guaíra exhibited positive balance of charge in subsurface, because the ΔpH was positive or, in other words, the pH measured in KCl 1N was higher than the pH measured in water. The Dusky-Red latosol (not acric) from Campinas had a ΔpH equal to zero and the other samples a negative ΔpH, indicating a predominance of negative over positive charges. The ZPSE had positive correlation with the gibbsite amount and negative correlation with the ki index

Conteúdo de carbono e atributos químicos de Latossolo sob cana-de-açúcar colhida com e sem queima

O objetivo deste trabalho foi avaliar o acúmulo de carbono e os atributos químicos de um Latossolo Vermelho distrófico em sistemas de colheita da cana-de-açúcar com (CQ) e sem queima (SQ), em experimento de longa duração. Em 2009, após 14 anos da implantação do experimento em Pradópolis, SP, amostras de solo foram coletadas na linha de plantio, a 0,25 m da linha e na entrelinha, nas profundidades de 0-0,05, 0,05-0,1, 0,1-0,2, 0,2-0,3 e 0,3-0,4 m. Foram determinados os teores de carbono orgânico total (COT), Ca2+, Mg2+ e K+ trocáveis, P-resina e P-Mehlich-1. Em geral, no sistema SQ, os teores de COT foram superiores na linha e a 0,25 m da linha, até a profundidade de 0,3 m. Na entrelinha, o acúmulo de carbono orgânico limitou-se às duas primeiras camadas superficiais. O sistema SQ também favoreceu a capacidade de troca catiônica e os valores de Ca2+, Mg2+ e saturação por bases, independentemente de locais de amostragem, nas duas primeiras camadas superficiais. O teor de P disponível foi pouco afetado pelos sistemas de colheita, com valores maiores no CQ. A colheita sem queima favorece o acúmulo de carbono orgânico e o aumento da fertilidade do solo, exceto quanto aos teores de P disponível

Sequential extraction of phosphorus in an Oxisol amended with biosolids in a long-term field experiment in Brazil

The continued growth of large cities is producing increasing volumes of urban sewage sludge. Disposing of this waste without damaging the environment requires careful management. The application of large quantities of biosolids (treated sewage sludge) to agricultural lands for many years may result in the excessive accumulation of nutrients like phosphorus (P) and thereby raise risks of eutrophication in nearby water bodies. We evaluated the fractionation of P in samples of an Oxisol collected as part of a field experiment in which biosolids were added at three rates to a maize (Zea mays L) plantation over four consecutive years. The biosolids treatments were equivalent to one, two and four times the recommended N rate for maize crops. In a fourth treatment, mineral fertilizer was applied at the rate recommended for maize. Inorganic P forms were extracted with ammonium chloride to remove soluble and loosely bound P; P bound to aluminum oxide (P-Al) was extracted with ammonium fluoride; P bound to iron oxide (P-Fe) was extracted with sodium hydroxide; and P bound to calcium (P-Ca) was extracted with sulfuric acid. Organic P was calculated as the difference between total P and inorganic P. The predominant fraction of P was P-Fe, followed by P-Al and P-Ca. P fractions were positively correlated to the amounts of P applied, except for P-Ca. The low values of P-Ca were due to the advanced weathering processes to which the Oxisol have been subjected, under which forms of P-Ca are converted to P-Fe and P-Al. The fertilization with P via biosolids increased P availability for maize plants even when a large portion of P was converted to more stable forms. Phosphorus content in maize leaves and grains was positively correlated with P fractions in soils. From these results it can be concluded that the application of biosolids in highly weathered tropical clayey soils for many years, even above the recommended rate based on N requirements for maize, tend to be less potentially hazardous to the environment than in less weathered sandy soils because the non-readily P fractions are predominant after the addition of biosolids. (C) 2012 Elsevier B.V. All rights reserved

Phosphorus Availability in an Oxisol Amended with Biosolids in a Long-Term Field Experiment

Many extractors are used to quantify available P in soils, but few studies have assessed the availability of P in soils of the wet tropics amended with high rates of biosolids. In this study, ion exchange resin, Mehlich-1 solution, and Fe-impregnated strips were used to quantify available P in samples from an Oxisol amended with surface-applied biosolids in a long-term field experiment. The soil's maximum capacity for P adsorption was also estimated. Experimental design consisted of randomized blocks, with four treatments and three replicates. Samples of biosolids were collected every year during the experiment, from 1999 to 2002. In 1999, two applications were made before growing maize (Zea mays L.) in austral summer and winter. Treatments were: Control (no biosolids added); B (biosolids added at rates based on their total N content); B2 (biosolids added at twice the rate of B), and B4 (biosolids added at four times the rate of B). Soil samples were collected at 0- to 0.1-, 0.1- to 0.2-, and 0.2- to 0.4-m depths. Biosolids were broadcast applied and incorporated into the soil to a depth of 0.2 m using a rotary hoe. The Oxisol had a high P-adsorption capacity (around 2450 mg kg(-1)) because of its high contents of clay and Fe and Al oxides. All the extractors were effective at assessing P availability and were positively correlated among themselves. Available P soil contents correlated positively with P content in maize leaves and grains, and the resin method yielded the highest correlation with P contents in leaves and grains

Cadmium Uptake by Lettuce (Lactuca sativa L.) as Basis for Derivation of Risk Limits in Soils

The availability and uptake of Cd by lettuce (Lactuca sativa L.) in two common tropical soils (before and after liming) were studied in order to derive human health-based risk soil concentration. Cadmium concentrations ranging from 1 to 12 mg kg(-1) were added to samples from a clayey Oxisol and a sandy-loam Ultisol under glasshouse conditions. After incubation, a soil sample was taken from each pot, the concentration of Cd in the soil was determined, lettuce was grown during 36 d, and the edible parts were harvested and analyzed for Cd. A positive linear correlation was observed between total soil Cd and the Cd concentration in lettuce. The amount of Cd absorbed by lettuce grown in the Ultisol was about twice the amount absorbed in the Oxisol. Liming increased the soil pH and slightly reduced Cd availability and uptake. CaCl2 extraction was better than DTPA to reflect differences in binding strength of Cd between limed and unlimed soils. Risk Cd concentrations in the Ultisol were lower than in the Oxisol, reflecting the greater degree of uptake from the Ultisol. The derived risk Cd values were dependent on soil type and the exposure scenario.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [07/56350-9