José Maria de Lima

Biological nitrogen fixation and phosphate solubilization by bacteria isolated from tropical soils

IntroductionIn addition to fixing atmospheric nitrogen, some bacterial isolates can also solubilize insoluble phosphates, further contributing to plant growth.AimsThe objectives of this study were the following: isolate, select, and identify nodulating bacteria in the cowpea that are efficient not only in biological nitrogen fixation (BNF) but also in the solubilization of insoluble inorganic phosphates; identify and quantify the organic acids produced; and establish the relationship between those acids and the solubilizing capacity.MethodsThe bacteria were captured from two soils containing high concentrations of insoluble phosphorus from the cities of Lavras and Patos de Minas, using the cowpea [Vigna unguiculata (L.) Walp.] as bait. We obtained 78 strains, which were characterized according to their cultural attributes in culture medium 79 with the strains UFLA 03-84, INPA 03-11B, and BR3267 (approved by the Ministry of Livestock and Supply Agriculture—MAPA, as inoculants for the cowpea) and Burkholderia cepacia (LMG1222T), which was used as a positive control for phosphate solubilization. Strains that were selected for their efficiency in both processes were identified by 16S rDNA sequence analysis. We evaluated the symbiotic efficiency (BNF) in a greenhouse and the solubilization efficiency of CaHPO4, Al(H2PO4)3, and FePO4.2H2O in solid and liquid GELP media. Strains that excelled at the solubilization of these phosphate sources were also evaluated for the production of the following organic acids: oxalic, citric, gluconic, lactic, succinic, and propionic.ResultsThe presence of Acinetobacter, Bacillus, Firmicutes, Microbacterium, Paenibacillus, and Rhizobium was detected by 16S rDNA sequencing and analysis. Bacterial strains obtained from cowpea nodules varied greatly in the efficiency of their BNF and phosphate solubilization processes, especially in the strains UFLA 03-09, UFLA 03-10, UFLA 03-12, and UFLA 03-13, which were more efficient in both processes. More strains were able to solubilize insoluble inorganic calcium and iron phosphates in liquid medium than in solid medium. The production of organic acids was related to the solubilization of CaHPO4 and FePO4.2H2O for some strains, and the type and concentration of the acid influenced this process.ConclusionsThese are the first results obtained with bacterial isolates from tropical soils in which the production of organic acids was detected and quantified to examine the solubilization of insoluble inorganic phosphates.

Efeito do pH na adsorção e dessorção de cádmio em Latossolos brasileiros

Adsorption and desorption reactions of metals in soils are influenced by the surface of the soil colloid attributes and solution composition. This study evaluated the effect of the pH on Cd adsorption (Cdads) and desorption (Cddes) in l7 Brazilian Oxisol samples that differed in their chemical, physical and mineralogical attributes. Samples of each soil, suspended in 5 mmol L-1 Ca(NO3)2 (pH adjusted to 4.5; 5.5, and 6.5; ratio soil:solution 1:67) were placed to react with 0.20 mmol L-1 Cd(NO3)2 (final ratio soil:solution 1:100) for 72 h, after which they were centrifuged and the Cd concentration of the solution determined. Thereafter, 25 mL of 5 mmol L-1 Ca(NO3)2 were added to the remaining residue to desorb the Cd retained in the soil samples. An increase of the pH solution from 4.5 to 5.5, from 4.5 to 6.5 and from 5.5 to 6.5 caused a 1.3; 2.2 and 1.7-fold increase in the Cd adsorption, respectively. The mean percentage of Cd adsorbed (Cd%ads) was 27 (pH 4.5), 35 (pH 5.5) and 55% (pH 6.5). The effect of soil attributes on Cdads was only evidenced at a pH of 5.5 and 6.5, by the correlations between Cdads and the soil organic matter, specific superficial area (SSA), CEC at pH 7.0 (CEC), kaolinite, hematite, oxalate-and-DCB-Fe and clay contents. However, only CEC and clay content, at pH 5.5 and the SSA, at pH 6.5, were included in the model of Cdads prediction, obtained through regression analyses. The adsorption in values of higher pH did not propitiate reduction in Cddes, which was around 20% for pH 4.5 and 40% for pH 5.5 and 6.5. The small proportions of Cd adsorbed by these Oxisols, mainly at lower pH values, which are an indication of high mobility and bioavailability, reinforces the need for the adoption of appropriate criteria to use or discard residues containing Cd in agricultural areas or close to aquifers.

Perdas de solo, água, nutrientes e carbono orgânico em Cambissolo e Latossolo sob chuva natural

Water erosion is responsible for considerable losses of nutrients and organic carbon from agricultural soils. The reduction of soil, water, nutrients and organic carbon losses constitutes an important aspect of the conservation planning. The objectives of this work were to evaluate the soil, water, nutrients and organic carbon losses from a Typic Dystrochept (TD) and a Rhodic Hapludox (RH). The samplings were performed after each considered erosive rain event. The mean annual soil losses were 205.65 Mg ha -1 for the TD and 14.90 Mg ha -1 for the RH. The mean annual water losses were 369 mm for the TD and 113 mm for the RH, representing 28.67% and 8.78% of the total precipitation, respectively. The mineralogical, chemical and physical attributes and the relief where these soils occur satisfactorily explain the obtained results. The TD presents higher nutrients and organic carbon losses than the RH. The organic carbon was the main component of the eroded sediment, evidenced by the selective character of erosion.

Relação entre atributos físicos, mineralogia da fração argila e formas de alumínio no solo

Aluminum (Al) is one of the most abundant elements in weight in Brazilian soils, found in different minerals and forms. Considering the lack of information about its participation in the physical behavior of soil, the present study aimed to evaluate the relationship between the mineralogy of the clay fraction, different forms of Al and physical attributes of different soils. Disturbed and undisturbed samples of A and B horizons of representative soils from the South and Campos das Vertentes physiographic regions in the State of Minas Gerais were therefore collected. The samples were subjected to physical, chemical and mineralogical characterizations. Correlation studies performed with the resulting data from the different characterizations showed that the physical attributes of the different studied soils are associated to the different forms of Al and to the mineralogy of the clay fraction: the amorphous and less crystalline forms of Al were more associated to physical attributes related with particle aggregation, such association being ascribed to the affinity of this element with organic matter, while the crystalline components were more associated to physical attributes related with the structural organization of the soils.

Mineralogia, química e estabilidade de agregados do tamanho de silte de solos da Região Sudeste do Brasil

The objective of this work was to evaluate the relationship of soil mineralogical and chemical composition with stability of silt-size aggregates. The studies were carried out using samples of A and B horizons of some soils from the Southeast Region of Brazil. Fine-earth samples were dispersed at 12,000 rpm during 20 minutes and the silt fraction was separated through clay fraction drain, constituting the fraction named pseudo-silt, which was sonificated, separating the desegregated clay fraction (by sonication) from the properly named silt fraction. Correlation analyses showed that the soil mineralogical and chemical compositions have marked influence upon clay dispersion, with reflections on the silt fraction. Higher amounts of gibbsite reflect in higher stability of silt-size aggregates, while the kaolinite promotes inverse effect. The Al forms determined on the pseudo-silt fraction are associated with higher difficult of dispersion of clay fraction of soils.

Avaliação de métodos indiretos de determinação da erodibilidade de Latossolos brasileiros

Existem tres maneiras de se determinar a erodibilidade do solo (Fator K). A primeira envolve a determinacao do fator K em condicoes de campo, sob chuva natural, a qual e onerosa e muito demorada. O segundo metodo e semelhante ao primeiro, porem baseia-se na quantificacao do fator K em razao das perdas de solo e do fator erosividade, sob condicoes de chuva simulada. O terceiro metodo baseia-se em regressoes multiplas que contenham, como variaveis independentes, atributos do solo correlacionados com o fator K obtido pelos dois metodos anteriores, tidos como padroes. A carencia de dados basicos e a indefinicao do melhor metodo para determinacao da erodibilidade de maneira indireta, que possibilite enquadrar os solos em classes de resistencia a erosao, constituem problemas na utilizacao destes metodos indiretos, particularmente nos Latossolos brasileiros. Portanto, objetivou-se com este estudo a determinacao indireta da erodibilidade desses solos e avaliacao da correlacao com os metodos diretos. Nenhum dos metodos testados mostrou-se recomendavel para a estimativa da erodibilidade para o conjunto de Latossolos do Brasil, sendo necessario, entao, desenvolver modelos especificos para este grupamento de solos.

Comportamento sortivo, individual e competitivo, de metais pesados em Latossolos com mineralogia contrastante

The pollution effect of trace elements in the environment depends mainly on the capacity of soil colloids to sorb and maintain them in high energy bonds. This study evaluated the adsorption of Cd, Cu, and Pb in A-horizon samples of Red Latosol and Red-Yellow Latosol (Udox), with similar texture and contrasting mineralogy. For this purpose, isotherms of adsorption, monoelement and multielement were built, based on the soil sample reaction in 5 mmol L-1 Ca(NO3)2 solution adjusted to pH 5.5, with metal concentrations of 0; 0.01; 0.05; 0.10; 0.15; and 0.75 mmol L-1. Desorption was then analyzed in 5 mmol L-1 Ca(NO3)2 solution. The isotherms were adjusted to the Langmuir model (P < 0.01). The maximum adsorption capacity of Cu and Pb was higher than of Cd in both soils. The simultaneous adsorption reduced the adsorption maximum capacity of the three metals. Cd was most reduced, indicating the lower competitive power than Cu and Pb. There was low reversibility of the adsorbed metals, indicating occurrence of hysteresis. The low competitive power of Cd, as indicated by the reduced maximum adsorption capacity in the presence of the other two metals, is alarming in weathered tropical soils, such as Oxisols.

Modelos matemáticos para predição da chuva de projeto para regiões do Estado de Minas Gerais

O uso de modelos matematicos para predicao da chuva e uma forma pratica e precisa para determinacao do valor a ser aplicado em projetos, sendo util para localidades desprovidas de informacoes pluviometricas. Objetivou-se ajustar o metodo de Bell, que possui caracteristicas de regionalizacao para a chuva de projeto, com base em equacoes de chuvas intensas e modelos de probabilidade de Gumbel de estacoes meteorologicas do Estado de Minas Gerais ajustando, tambem, um modelo para cada regiao do estado. Avaliaram-se os modelos considerando-se o coeficiente de determinacao e os erros medios em relacao aos dados originais. Para validacao, trabalhou-se com tres estacoes meteorologicas da regiao Norte nao usadas para ajuste do respectivo modelo. Foram analisadas tres metodologias para estimativa da chuva intensa padrao (h(60,2)), que pondera o metodo usado, ressaltando-se a media aritmetica, a media ponderada pelo inverso do quadrado da distância e a predicao geoestatistica (krigagem). Observou-se que os modelos possuem bons indicadores estatisticos e a validacao produziu erros baixos, mostrando que os modelos podem ser aplicados, especialmente se a krigagem for usada para estimativa do parâmetro h(60,2).

Lead sorption and leaching from an Inceptisol sample amended with sugarcane vinasse

A vinhaca e produzida em grandes quantidades pela industria de etanol e de aguardente (cachaca). Embora os efeitos da vinhaca nos atributos do solo sejam bem conhecidos, pouco se sabe sobre eles no comportamento sortivo de chumbo (Pb). Avaliaram-se a sorcao e a lixiviacao de Pb em amostras da camada superficial (0-20 cm) de um Cambissolo Haplico Tb Distrofico tipico (CXbd) sob influencia da vinhaca. Para o ensaio de sorcao, as amostras foram peneiradas em malha de 2 mm, tratadas com vinhaca diluida 20% e 50% e ao natural (100%), empregando agua destilada nas amostras controle. Em seguida, solucoes com 0,05; 0,10; 0,25; 0,50 e 0,75 mmol L-1 de Pb foram adicionadas as amostras de solo. Para o ensaio de lixiviacao, foram preparadas colunas de solo em tubos de PVC de 12 cm de altura e 4 cm de diâmetro interno, contendo 200 g de solo. As doses de vinhaca aplicadas sobre as colunas foram correspondentes a 150 e 300 m3 ha-1. As colunas foram mantidas incubadas com vinhaca por sete dias. Apos esse periodo, foram aplicados sobre cada coluna 5 mL de uma solucao de concentracao 100 mmol L-1 de Pb e, posteriormente, realizadas sucessivas lixiviacoes, coletando-se o percolado para determinacao do teor de Pb. A vinhaca aumentou a capacidade maxima de adsorcao de Pb e sua energia de ligacao com o solo em condicoes de equilibrio (ensaio de sorcao), mas em condicoes de nao equilibrio (ensaio de lixiviacao em colunas), a vinhaca aumentou a lixiviacao de Pb. Com base nesses resultados, atencao especial deve ser dada a areas que estejam recebendo vinhaca ao longo dos anos e que estejam ocasionalmente sujeitas a contaminacao por Pb.

Efeito da adsorção de fosfato em parâmetros físicos e na compressibilidade de solos tropicais

High phosphate adsorption in oxidic tropical soils changes the charge balance on the surface of particles and can increase dispersion. Consequently, it can affect pore size distribution, aggregate stability and susceptibility to compaction. In order to measure the effect of phosphate sorption on compression curves and consistence limits, a Dark-Red Latosol (LE) (very fine, allitic, isothermic Typic Hapludox) and a Cambisol (C) (very fine, isothermic Oxic Distropept) were sampled at 0-3 and 27-30 cm depth, at Campos da Mantiqueira, Minas Gerais, Brazil. Phosphate solution was added to half of the samples so that the P adsorption capacity could be reached. Preconsolidation pressures were obtained from the compression curves, which represent the bulk density of soil as a function of log of applied load. Liquid, plastic, and contraction limits were also determined for each sample under both P and no P conditions. The results showed a shift on compressibility curves towards lower preconsolidation pressures as moisture increased and P was adsorbed to samples. This shift was more evident on LE samples, mainly at 0-3 cm depth, which means a decrease on the load support capacity of soil. Phosphate adsorption also changed consistency limits, decreasing the range of friability and, consequently, affecting trafficability and workability of soil.