Ary Carlos Xavier Velloso

Estoque e qualidade da matéria orgânica de um solo cultivado com cana-de-açúcar por longo tempo

The aim of this study was to evaluate the stocks, and quality of the soil organic matter (SOM) through the use of solid state 13C nuclear magnetic resonance (13C NMR), electronic paramagnetic resonance (EPR) and fluorescence spectroscopy of a fine clay fluventic Eutrichrept after long-term sugarcane cultivation. In one area, sugarcane has been grown for 55 years no field burning before harvest. In another area managed under the traditional system the crop field has been burned before harvest for 35 years; vinasse has been applied on one part (at a rate of 120 m3 ha-1 yr -1), but not on another. The increases of 157 and 57 % in C stocks of humic acids in the area cultivated without field burning for 55 years were related with the increase in the aromaticity degree as well as lower acidity of the SOM, as shown by 13C NMR spectroscopy. The semiquinone-type free radical concentration, as observed by EPR, and intensity of fluorescence emission were higher in the humic acid extracted from soils under management system without field burning before harvest. Significant changes in the humification process were observed in the areas with crop trash preservation. However, in areas where sugar-cane fields were burnt at harvest, vinasse application for 35 years resulted in only minor changes in the organic matter quality and C stocks. These data indicate a rapid evolution of the soluble organic matter added to the soil through vinasse application.

Biomassa e estoque de carbono e nutrientes em florestas montanas da mata atlântica na região norte do estado do Rio de Janeiro

Os estudos sobre balanco de C e nutrientes em florestas naturais permitem avaliar possiveis alteracoes decorrentes de tecnicas de manejo aplicadas e possibilitam inferir a sustentabilidade dessas florestas. Os objetivos deste trabalho foram avaliar o teor de nutrientes de especies nativas e quantificar a biomassa (parte aerea + serapilheira) e os estoques de C e nutrientes em fragmentos florestais montanos da Mata Atlântica (Floresta Ombrofila Densa Montana) na regiao norte do Estado do Rio de Janeiro, no periodo de maio de 1999 a abril de 2001. Foram selecionados dois fragmentos, localizados a 900 e 600 m de altitude, na vertente atlântica do Parque Estadual do Desengano, RJ. O solo de ambos os fragmentos florestais foi classificado como Cambissolo Haplico Tb distrofico. O valor medio de biomassa (parte aerea + serapilheira) foi de 166,8 Mg ha-1. Em consequencia, a acumulacao media de C na vegetacao foi de 67, 2 Mg ha-1. Os estoques medios de N, P, K, Ca e Mg na vegetacao foram de 1.152, 44,4, 276,5, 603,5 e 127,9 kg ha-1, respectivamente. Por outro lado, as especies revelaram distinta capacidade de estoque de nutrientes. O balanco negativo de P, K e Ca {solo - (parte aerea + serapilheira)} indica que esses elementos constituem principais fatores nutricionais limitantes ao crescimento dos fragmentos florestais montanos da Mata Atlântica na regiao norte-fluminense.

Propriedades redox e grupos funcionais de ácidos húmicos isolados de adubos orgânicos

According to the system conditions, humic acids act as oxidants or as reductants. In natural systems the electron flow is directly associated with humus content and quality. Electrode potential and oxidation capacity inform about the intensity and capacity of the redox systems. In previous studies it has been assumed that free radicals participate in humic acid redox reactions. In our study six humic acids isolated from composed organic residues were titrated with an oxidant (I2) in inert atmosphere and specified conditions. Humic acids presented similar standard formal electrode potentials, with values between 0.773 and 0.794 V, at 25 oC. The oxidation capacity of humic acids varied from 3.88 to 4.39 molc kg-1 at pH 5.0 and from 5.35 to 7.89 molc kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the concentrations of the phenolic, quinone and semiquinone functional groups in the humic acids.

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.

Redox index of soil carbon stability

Como alternativa aos relativamente complexos e dispendiosos metodos espectroscopicos, as propriedades redox dos acidos humicos, determinadas por titulacao potenciometrica, vem sendo usadas na avaliacao da estabilidade do C do solo. O objetivo deste estudo foi estabelecer um indice redox de estabilidade do C (RICS) e correlaciona-lo com alguns atributos de diferentes solos modais brasileiros (distintos estadios de intemperismo ou manejo), a fim de mais facilmente comparar sistemas. O RICS foi eficiente para comparacao de solos e variou similarmente com os metodos quimicos e espectroscopicos usados na caracterizacao dos acidos humicos. Os valores de pH, ponto de efeito salino nulo zero, soma de bases, teor de calcio trocavel, indice de intemperismo, bem como de razao entre oxigenio e carbono, teores de quinonas e de radicais livres semiquinonas, carbono aromatico e intensidade de fluorescencia dos acidos humicos, mostraram estreitas relacoes com o RICS. Os solos menos intemperizados, com argilas mais ativas e mais alta fertilidade apresentaram maior RICS. Os solos sob longo tempo de manejo com cana-de-acucar mostraram RICS seguindo a ordem decrescente: cana crua, cana queimada com vinhaca, cana queimada sem vinhaca.

Initial performance of pineapple and utilization of rock phosphate applied in combination with organic compounds to leaf axils

Rock phosphates have low solubility in water, but good solubility in acid. The use of or ganic compounds together with these phosphorus sources applied to the basal leaf axils of pineapple can increase the solubility of this phosfate source and increase the P availability to the crop. A greenhouse experiment was conducted using Araxa rock phosphate (10 g) in combination or not with solutions containing increasing concentrations of humic acids (0 to 40 mmol L -1 of carbon), with or without citric acid (0.005 mmol L -1 ), applied to basal leaf axils of pineapple cv. Perola. Growth and nutritional characteristics of aerial plant parts were assessed. Growth rates of aerial parts and N, P , K, Ca and Mg contents increased curvilinearly with increasing concentration of carbon in the form of humic acids. Maximum values were found for the concentration of 9.3 mmol L -1 of carbon combined with 0.005 mmol L -1 of citric acid and natural phosphate.

Eletroquímica de solos modais e de sua matéria orgânica em ambientes tropicais

Soil chemistry soils studies the behavior of the mineral fraction of weathered tropical soils, including electrochemistry, development of charges and adsorption phenomenon. Because of the broad spectrum to be covered in the understanding of the behavior of mineral fraction added to the methodological difficulties, the study of complex soil organic fraction was relatively less developed. The current proposal revisits the early works related to the chemistry of tropical soils with the objective to relate them with electrochemical data of soil carbon stocks. The objective of this study was to review aspects of soil electrochemistry, to determine and to relate the points of zero charge by different methods, the potentials of the electric double layer and the electrochemistry of humus of Brazilian modal soils in a typical sequence of weathering, aiming to generate information for their management and conservation. The methods for estimating the point of zero charge of the soils show different results, but with the same trend among soils. There is a predominance of negative charges on both layers of soils. The negative charges of the colloids are significantly associated with the availability of electrons from the humus and both decrease with the weathering stage of the soil.

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.

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.