Marcelo Luiz Simões

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.

Carbon stock and humification index of organic matter affected by sugarcane straw and soil management

The maintenance of sugarcane (Saccharum spp.) straw on a soil surface increases the soil carbon (C) stocks, but at lower rates than expected. This fact is probably associated with the soil management adopted during sugarcane replanting. This study aimed to assess the impact on soil C stocks and the humification index of soil organic matter (SOM) of adopting no-tillage (NT) and conventional tillage (CT) for sugarcane replanting. A greater C content and stock was observed in the NT area, but only in the 0-5 cm soil layer (p < 0.05). Greater soil C stock (0-60 cm) was found in soil under NT, when compared to CT and the baseline. While C stock of 116 Mg ha-1 was found in the baseline area, in areas under CT and NT systems the values ranged from 120 to 127 Mg ha-1. Carbon retention rates of 0.67 and 1.63 Mg C ha-1 year-1 were obtained in areas under CT and NT, respectively. Laser-Induced Fluorescence Spectroscopy showed that CT makes the soil surface (0-20 cm) more homogeneous than the NT system due to the effect of soil disturbance, and that the SOM humification index (HLIF) is larger in CT compared to NT conditions. In contrast, NT had a gradient of increasing HLIF, showing that the entry of labile organic material such as straw is also responsible for the accumulation of C in this system. The maintenance of straw on the soil surface and the adoption of NT during sugarcane planting are strategies that can increase soil C sequestration in the Brazilian sugarcane sector.

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.

The influence of seasonalness on the structural characteristics of aquatic humic substances extracted from Negro River (Amazon State) waters: interactions with Hg(II)

In this work, humic substances were extracted from water samples collected monthly from the Negro River basin in the Amazon state (Brazil) to study their properties in the Amazonian environment and interactions with the mercury ion considering the influence of seasonalness in this formation. The C/H, C/N and C/O atomic ratio parameters, functional groups, concentration of semiquinone-type free radicals, pH, pluviometric and fluviometric indices, and mercury concentrations were interpreted using hierarchical cluster analysis (HCA) and principal component analysis (PCA). The statistical analyses showed that when the pluviometric index was greater and the fluviometric index was smaller, the degree of humification of aquatic substances was greater. The following decreasing order of the degree of humification of the AHS collected monthly was established: Nov/02 to Feb/03 > Mar/02 to May/02 > Jun/02 to Oct/02. The greatest concentrations of mercury were detected in more humidified samples. These results suggest that due to inter and/or intra-molecular rearrangements, the degree of humification of aquatic humic substances is related to its affinity for Hg(II) ions.

Ácidos Húmicos em solo fertirrigado no Vale do São Francisco

A aplicacao de acidos orgânicos, principalmente humicos (AH), associada a adubacao mineral e orgânica pode levar a alteracoes nas propriedades dos AH do solo. No Vale do Sao Francisco, o uso de acidos orgânicos vem despertando o interesse de produtores que usam sistema de irrigacao. Entretanto, nao sao conhecidas as modificacoes que podem ocorrer nas caracteristicas das substâncias humicas do solo quando sao aplicados acidos orgânicos associados a fertilizacao mineral e estercos. Os objetivos deste trabalho foram avaliar e caracterizar, por metodos espectroscopicos (UV-Vis, Infravermelho, Fluorescencia e RPE), as possiveis mudancas qualitativas no AH extraido de solo fertirrigado com duas fontes de fertilizantes (orgânica e mineral), associadas a aplicacao de acidos orgânicos comerciais na cultura da goiabeira. O experimento foi conduzido na Embrapa Semiarido, em Petrolina - PE. Os tratamentos utilizados foram: F - fertirrigacao com fertilizantes minerais (ureia, fosfato monoamonio, cloreto de potassio); FE - F + aplicacao de 20 dm3/planta de esterco; FH - F + fertirrigacao com 30 dm3 ha-1 de Codahumus 20®; FEH - fertirrigacao mineral + aplicacao de 20 dm3/planta de esterco + fertirrigacao com 30 dm3 ha-1 de Codahumus 20®, e R- tratamento testemunha, sem adubacao. A relacao E4/E6 dos AH variou de 4,8 a 5,4 para os tratamentos FEH e F. Os dados obtidos por meio da espectroscopia FTIR sugerem mistura de caracteristicas aromatico-alifaticas, grande quantidade de grupos carboxilicos e menor numero de grupos nitrogenados para os AH dos tratamentos FEH, FH e FE. Os valores obtidos do indice A465 variaram de 1,04 a 1,74, referentes aos AH dos tratamentos FEH e FE. Verificou-se uma concentracao de radicais livres orgânicos no AH do tratamento FEH (2,66 spins g-1 1017) tres vezes maior do que o AH do tratamento F (0,95 spins g-1 1017). O esterco foi o responsavel pelo maior de policondensacao e grau de humificacao do acido humico dos tratamentos FE e FHE.

Determination of metal ions extracted by DTPA in a soil treated with effluent using an Hg-electroplated-Pt microelectrode

Determinations of Cu, Fe, Mn and Zn were performed in an oxisol soil treated with effluent originated from a biodigester septic cesspool. The extracts were obtained from a DTPA/TEA (pH 7.3) solution and analysed by electroanalytical methodologies using square wave anodic stripping voltammetry (SWASV) for the analysis of Cu, Mn and Zn and square wave voltammetry (SWV) for Fe analysis, both of them with a thin mercury film microelectrode (ME-Hg). DTPA (diethylenetriaminepentaacetic acid) complexes with Cu, Mn and Fe show electroactivity in the potentials range close to the ones for the free ions in solution, but the Zn complex did not show any electroactivity at the potential range analysed. SWASV/ME-Hg and SWV/ME-Hg results were in good agreement (r2 = 0.996) with the flame atomic absorption spectroscopy (FAAS) analyses, demonstrating that electroanalytical methodologies can be used for micronutrient determinations in soil extracts without serious interferences of the matrix components. Some characteristics of the complex formed between DTPA-metals are explored by EPR experiments.

Viabilidade do emprego de ácido fluorídrico 10% para a remoção de íons paramagnéticos em amostras de solos e suas respectivas frações físicas

ABSTRACT: Treated sewage effluent utilization for irrigation represents an antique, popular and attractive alternative to the common disposal of effluent to watercourses and includes three main purposes: effluent complementary treatment, water and nutrient source to the soil-plant system. However, because in Brazil no experiences in wastewater recycling exists consequent-ly few scientific studies were carried out despite the importance of the subject. The present study aimed to evaluate by chemical and spectroscopy techniques the soil organic matter from soils irrigated with treated sewage effluent. Five treatments were evaluated: TSI (control) - irrigation with potable water and addition of the nitrogen as mineral fertilizer; T100, T125, T150 and T200 - irrigation with treated sewage sludge effluent and addition of the nitrogen as mineral fertilizer. The results obtained shown changes in the carbon contend and humification degree for the soils irrigated with treated sewage sludge effluent due to the increase activity of the decomposition of organic matter, stimulated by the increase of water in the soil.