Carlos Eduardo Rezende

Organic matter quality in a soil cultivated with perennial herbaceous legumes

Using herbaceous legumes in agricultural systems yields great quantities of plant residues, allowing changes in soil organic matter quality and content over the years. This study was conducted on an Ultisol, at Seropedica, RJ, Brazil, to evaluate the effects of different perennial herbaceous legumes on soil organic matter quality. A factorial scheme with three replications was used to evaluate the species: forage groundnut cv. BR-14951 (Arachis pintoi), tropical kudzu (Pueraria phaseoloides), and siratro (Macroptilium atropurpureum). After the first cut, each plot was divided into two subplots; plants were cut and left on the soil surface or cut and removed. Soil samples of a closed area covered by spontaneous vegetation (mainly C3 plants) or by Panicum maximum were also analysed. Samples were collected from two layers (0-5 and 5-10 cm), processed for the fractionation of organic matter and the evaluation of structural characteristics of humic acids (HA). Evaluated legumes did not change total organic carbon contents, but promoted HA accumulation in the superficial soil layer. Humic acids may be used as indicators of the management effects on soil organic fractions, because there was significant incorporation of carbon and nitrogen derived from the legume residues, even for the short experimentation time (28 months). Residue management did not modify quantitative aspects of the distribution of the humified organic matter, but promoted, however, a higher condensation degree of humic acids evaluated by the elementary composition, IR and fluorescence spectroscopy.

Promoção do crescimento radicular de plântulas de tomateiro por substâncias húmicas isoladas de turfeiras

As turfeiras constituem uma reserva importante de C humificado nos ecossistemas terrestres. O interesse pelo uso de substâncias humicas como agentes promotores do crescimento vegetal vem crescendo continuamente. O objetivo deste trabalho foi avaliar a bioatividade das substâncias humicas alcalino soluveis (SH), acidos humicos (AH) e fulvicos (AF) isolados de turfeiras com materia orgânica em diferentes estadios de decomposicao da materia orgânica (saprica, hemica ou fibrica) localizadas na Serra do Espinhaco Meridional, MG. Foram obtidas curvas de dose-resposta para o numero de raizes emergidas do eixo principal em plântulas de tomateiro. Os resultados mostraram que os AH foram mais bioativos (maior inducao de raizes laterais com menor dose) enquanto a maioria dos AF nao promoveu o crescimento radicular. Tanto SH como AH estimularam o aparecimento de pelos radiculares. Em baixas concentracoes, SH e AH induziram o aparecimento de pelos proximos a coifa, tipico de plantas com desbalanco hormonal. O uso do tomateiro transgenico com gene reporter DR5::GUS permitiu a observacao da inducao de rotas de sinalizacao ligadas a acao das auxinas na promocao do crescimento radicular pelos AH.

Eletroquímica de latossolos brasileiros após a remoção da matéria orgânica humificada solúvel

A eletroquimica e a concentracao de materia orgânica nos horizontes superficiais de Latossolos correlacionam-se estreitamente. No presente trabalho, avaliaram-se as propriedades eletroquimicas do horizonte superficial de sete Latossolos brasileiros apos a remocao das substâncias humicas em meio alcalino. Os solos foram separados em dois grupos, segundo sua mineralogia, caulinitica e oxidica. O extrator NaOH 0,1 mol L-1 solubilizou substâncias humicas correspondentes a menos de 3 % da MO total, indicando forte adsorcao especifica do material orgânico a fracao mineral. A extracao de acidos humicos e fulvicos foi capaz de inverter o sinal de carga da superficie; no entanto, o efeito mais acentuado da retirada das substâncias humicas soluveis foi a perda da capacidade-tampao das cargas do solo. A capacidade da dupla camada eletrica, uma medida indireta desse poder-tampao, aumentou de 3 a 15 vezes depois da extracao das substâncias humicas alcalino-soluveis. Solos com mineralogia predominantemente oxidica apresentaram maiores valores do ponto de efeito salino nulo, da capacidade da dupla camada eletrica, alem da diminuicao na capacidade de troca de cations do que aqueles de natureza caulinitica.

Propriedades redox de ácidos húmicos isolados de um solo cultivado com cana-de-açúcar por longo tempo

Soil organic matter is the largest carbon reservoir in natural systems. In such systems the carbon quality and stability can be estimated based on the increase of humified fractions which, among other factors, is related to the balance between losses and accumulations involving oxidation and reduction reactions of the soil organic matter. The objective of this study was to evaluate the electrochemistry of humic acids isolated from soils cultivated continually with sugar-cane, with or without pre-harvest burning and annual vinasse application using iodimetric redox titrations. The formal electrode potentials of the humic acids had a similar pattern, with values between 0.760 and 0.779 V, at 25 oC. The oxidation capacity of humic acids varied from 1.01 to 3.44 molc kg-1 at pH 5.0 and from 1.64 to 6.44 molc kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the humic acid contents of phenolic, quinone and semiquinone functional groups.

Bacterial Biodegradation of Petroleum and Oil Compounds

Petroleum compounds can be degraded by several bacterial species. Thus, these microorganisms are of great interest to the industry and to the recovery of contaminated environments. Methods to isolate, cultivate and identify bacteria able to degrade these pollutants have been developed in the field of chemistry, biochemistry, microbiology and molecular biology, allowing for a better understanding of bacterial communities ecology and dynamics in the environmental context and in the laboratory. Finally, there is a growing need for multidisciplinary research in order to meet the greatest possible number of species, their metabolic properties and their respective roles in the degradation process of oil compounds and, with this information, develop strategies for decontamination of environments polluted with these substances.

Propriedades redox da matéria orgânica isolada de material ultrafiltrado das águas do rio Paraíba do Sul

Previous studies indicated that free radicals control organic matter redox activities. In the present study, organic matter of an ultra-filtrated material collected from seven samples taken seasonally from the Paraiba do Sul River for two years were titrated with an oxidizer (I2) in an inert atmosphere. Standard formal potential values for the electrode MOOx, MORed ranged from 0.754 to 0.786 V at a 25 oC temperature. Organic matter oxidation capacity (COx) per carbon mass varied according to pH values, and changes in COx were related to rainfall and river flow intensities.