Wilson Tadeu Lopes da Silva

Estudo comparativo de métodos para a determinação da concentração de carbono em solos com altos teores de Fe (Latossolos)

Soil organic matter (SOM) plays an important role in physical, chemical and biological properties of soil. Therefore, the amount of SOM is important for soil management for sustainable agriculture. The objective of this work was to evaluate the amount of SOM in oxisols by different methods and compare them, using principal component analysis, regarding their limitations. The methods used in this work were Walkley-Black, elemental analysis, total organic carbon (TOC) and thermogravimetry. According to our results, TOC and elemental analysis were the most satisfactory methods for carbon quantification, due to their better accuracy and reproducibility.

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.

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.

Avaliação físico-química de efluente gerado em biodigestor anaeróbio para fins de avaliação de eficiência e aplicação como fertilizante agrícola

The use of biodigester for basic and environmental sanitation has large demand in Brazil. A biodigester was built to treat conjunctly the human and pig feces and urine, regarding to its future application in rural small towns. The results show that the biodigester can reduce 90% of COD and BOD and, up to 99.99% of thermotolerant coliforms. The treated effluent has variable quantities of macro- and micro-nutrients; and organic matter. However, the concentration variability of the nutrients makes difficult a dosed application into soil. The soluble salts (mainly as Na+ form) make necessary a controlled use to avoid environmental degradation.

Espectroscopia de infravermelho na determinação da textura do solo

A aplicacao de tecnicas espectroscopicas que utilizam a radiacao infravermelha (NIRS-Near Infrared Spectroscopy e DRIFTS-Diffuse Reflectance Fourier Transformed Spectroscopy) na analise inorgânica do solo tem sido proposta desde a decada de 1970, mas ate os dias atuais sao raros os metodos implementados rotineiramente no Brasil. Isso deve-se a dificuldade em construir modelos de calibracao, por meio de metodos estatisticos multivariados, utilizando-se amostras reais de solo, de constituicao complexa, que varia geograficamente e de acordo com o manejo. Por isso, os objetivos deste trabalho foram construir modelos de calibracao em NIRS e DRIFTS para a quantificacao das fracoes de argila e areia, em amostras de solos de classes diferentes - Latossolo Vermelho (predominante), Nitossolo, Argissolo Vermelho e Neossolo Quartzarenico - e avaliar qual dessas duas tecnicas e mais adequada para essa finalidade, assim como a interferencia do agrupamento de amostras e da selecao de variaveis espectrais na qualidade desses modelos. Para isso, valores de referencia obtidos pelo metodo do densimetro, metodo largamente utilizado nos laboratorios de analise de solo, foram correlacionados com valores de absorbância em NIRS e DRIFTS pela ferramenta estatistica PLS (Partial Least Squares), obtendo-se altos coeficientes de determinacao (R2), de 0,95, 0,90 e 0,91 para argila, silte e areia, respectivamente, na validacao externa. Isso confirma a aplicabilidade das tecnicas espectroscopicas na analise granulometrica do solo para fins agricolas. O agrupamento das amostras segundo a localizacao e a selecao de variaveis espectrais pouco influenciou na qualidade dos modelos. A tecnica espectroscopica mais indicada para essa finalidade foi a DRIFTS.

Effect of humic substances on the electrochemical reduction of p-nitrophenol

p-Nitrophenol (PNP) is the main hydrolysis product of methylparathion (MP), one of the most commonly used organophosphate insecticides in the world. Such a product is very toxic for human and animals. Humic substances (HS) are natural recalcitrant organic matter found in soil and waters that have an ability to interact, immobilize, and degrade pesticides. This article presents electroanalytical and UV-Visible studies, conducted to understand the effect of the HS on the PNP reduction process and therefore to understand how the HS can influence PNP degradation in the environment. Electroanalytical results showed that the HS benefit the reduction of the nitro-group of PNP by electrocatalysis. UV-Visible spectra showed that the catalytic effect of HS occurs due to the interection between the PNP and the HS followed by a proton donor mechanism.

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.

Comportamento de herbicidas com efeito residual em diferentes coberturas na cultura do feijoeiro

The objective of this work was to evaluate the performance of residual herbicides applied pre planting in different vegetal coverings under no-till system before dry bean crop establishment in 1999 and 2000. Each herbicide was applied separately in five different coverings, totaling twenty experiments. The herbicides and respective dosages were: diclosulan (0.0125 kg ha1), sulfentrazone (0.300 kg ha-1), dimethenamid (1.125 kg ha-1) and S-metolachlor (1.152 kg ha1). In Santo Antonio de Goias, Brazil, Pennisetum glaucum dry plants and dry weeds (Commelina benghalensis and Bidens pilosa) were used under the integrated control system (ICS); and in Santa Helena de Goias sorghum dry plants were used under the (ICS) system and green Pennisetum glaucum and green weeds (Commelina benghalensis and Bidens pilosa) under the Apply and Sow system in 1999/2000. Each experiment consisted of 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 e 20 t ha-1 of biomass of different vegetal coverings, each receiving the five herbicides separately in a completely randomized design, with three replicates. The amount of herbicide left in the soil was determined in a bioassay, with Sorghum bicolor being used as a control plant. The results showed that 80% of the applied doses of diclosulan and sulfentrazone were present in soil independently of the amount and type of soil covering. For dimethenamid and S-metolachlor, up to 50% of the amount applied was detected in soils with 8 t ha-1 of plant residues.

Redução da interferência de Brachiaria decumbens na formação de pastagem com Penisetum purpureum através de herbicidas

Two experiments were carried out to evaluate elephant-grass tolerance to different herbicides sprayed alone or in mixtures in pre- and post-emergence crop conditions, and to evaluate the efficiency of these products in controlling B. decumbens and other weeds infesting the elephantgrass crops. Herbicide treatments evaluated in the experiment installed in pre-emergence of the crop, in kg ha-1 were: metolachlor (1.152; 2.304 and 3.456), oxyfluorfen (0.48; 0.96 and 1.44) and atrazine + metolachlor (1,25; 2,50; e 3,75), plus the controls, in three repetitions; The herbicide treatments evaluated in the experiment installed in post-emergence conditions, in kg ha-1, were: ametryne (1.25; 2.50 and 3.75) and oxyfluorfen (0.48; 0.96 and 1.44), in four repetitions. The treatments were distributed in randomized blocks in both experiments, with added as treatments (weeded and weed-free), using the elephant-grass cultivars Cameroon and Pioneer. Herbicides in post-emergence were applied on the cultivar plant tops, at 20 days after planting, and in the pre-emergence experiment, one day after planting, and the soil was wet at the moment of herbicide application. Metolachlor, atrazine + metolachlor and oxyfluorfen applied in pre-emergence were selective for Pioneer and Cameroon cultivars. Ametryne and oxyfluorfen were also selective for cultivars when sprayed in post-emergence conditions. Because of initial damages to the crop, oxyfluorfen application in the dose of 1.44 kg ha-1, as well as, in pre- and post-emergence of the crop, combined with ametryne application in the dose of 3.75 kg ha-1 in post-emergence, must be avoided. B. decumbens and B. brizantha were controlled in 90.9% in pre-emergence, when intermediate and higher doses of the herbicides were used. Dicotyledonous plant control was 85% with metolachlor, atrazine + metalachlor and oxyfluorfen, except when the lowest doses were applied. In pre-emergence application, ametryne doses of 2.50 and 3.75 kg ha-1 and oxyfluorfen in the three doses studied provided a control level over 90% in B. decumbens, B. brizantha, S. glaziovii and S. urens, while D. tortuosum, and A. australe control was over 77.9%. In either pre- or in post-emergence application, residual effect of weed control was up to 90 days after application. Treatments with pre-emergence herbicides were 36.2% higher in cultivar height evaluated in pre-emergence and 34.7% higher in height in post-emergence, than the treatment weeded. As for above ground shoot dry matter accumulation, cultivars presented mean earnings of 48.8% in the treatments with pre-emergence herbicides and of 61.9% in post-emergence herbicides, compared to weeded. The cultivar Pioneer was more tolerant to weed interference than the cultivar Cameroon.

Avaliação da eficiência de herbicidas no controle de plantas daninhas em alfafa

The objectives of this study were to evaluate the efficiency and selectivity of herbicides on the weed plants control at the alfalfa crop. Two experiments were carried out at the Experimental Station of Agenciarural, located in Anapolis, GO. In the first experiment it was evaluated eight herbicides (imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl and imazamox) post emergency and in the second experiment six different mixed of herbicides [(diuron + MSMA), (diuron + MSMA), (diuron + paraquat), (diuron + paraquat)] applied one day after the alfalfa harvesting date. For both experiments were included two checks (weedy check and no weedy check) and it was used a randomized block design, with four replications. The herbicides imazethapyr, MSMA, fomesafen, bentazon, chlorimuron-ethyl and imazamox were selective to the alfalfa crop and efficient for the weed plants control. The mixed of herbicides (diuron + MSMA) and (diuron + paraquat) applied after the harvesting date were responsible for damage on leaves and stem remaining. Although the new alfalfa budding did not show any signal of toxic and the development and growth was normal. These mix of herbicides showed an efficient weed plants control and did not affect the harvest dry matter and plant height comparing to the weedy check. The no weedy check reduced the plant dry matter and height in 74,5% and 42,8%, respectively.