Eduardo de Sá Mendonça

Caracterização dos ácidos húmicos extraídos de um latossolo vermelho-amarelo e de um podzol por análise termodiferencial e pela espectroscopia de absorção no infravermelho

The spectroscopic characterization of humic substances in soil has been widely used. However, few studies have been carried out concerning the pedology of tropical soils using such technique. Humic acids (HA) extracted from contrasting horizons of a Red Yellow Latosol and a Podzol, on the highlands of the Serra do Brigadeiro, Araponga, Minas Gerais, were characterized by means of Fourier Transformed Infrared Absorption Spectroscopy (FTIR) and TD analysis. The spectra indicated qualitative differences between the HA extracted from differing soils, and also between HA extracted from different horizons in a given soil. The peaks associated with aliphatic structures showed decreasing intensity with soil depth, and there were evident polissacaride-related peaks in the organic horizons. Mineral impurities could be detected in all HA spectra of non-purified samples. The HF-HCl treatment was efficient in removing of these mineral impurities, with the differential spectra between purified and non-purified HA revealing the presence of caolinite and gibbsite. After the HA purification, an increase in intensity for the peaks of carboxyl groups was observed, suggesting the role of such groups in the process of mineral-HA interaction. The TD analysis indicated a greater resistance to thermodegradation of the humic acid extracted from Podzol horizon Bhs, as compared to the humic acid extracted from Latosol horizon A. This agrees with the more aromatic fashion of the former, shown in the infrared spectrum analysis.

Avaliação de frações da matéria orgânica do solo para caracterização de áreas degradadas

The characterization and quantification of soil organic matter as water soluble carbon, labile carbon and light organic matter may be used to characterize the rehabilitation of degraded areas. Soil samples were thus collected on a hillside cut submitted to reclamation, presenting different types of vegetal covering during November 1994, in the district of Vicosa. The treatments consisted of areas of soils without vegetation, recovering areas with mainly legumes, recovering areas with mainly grass, soils under grass and soils under natural forest. The results have shown that the fractionation of organic carbon in soluble carbon in saline solution, water soluble carbon, light organic matter help to characterize the degraded areas. The soluble carbon in saline solution seems to be the best method to characterize the degraded areas from different vegetal covers.

Alterações edáficas sob plantios puros e misto de espécies florestais nativas do sudeste da Bahia, Brasil

The objective of this study was to evaluate the relation between the chemical composition of litter accumulation and its effect on the physics and fertility of soil in two plantation systems of native forest species. The plantation systems consisted of 22 year-old mixed stand and pure stands of six hardwood species (Peltogyne angustiflora, Centrolobium robustum, Arapatiella psilophylla, Sclerolobium chrysophyllum, Cordia trichotoma, Macrolobium latifolium) native to the southeastern region of Bahia, Brazil, evaluated from August 1994 through November 1996. As a reference for the characteristic analyzed, the study included a secondary forest near climax, and a 40 year-old naturally regenerated forest. The soil of the 0-5 cm upper layer was better structured in the mixed stand than in the other forest systems. This layers soil structure was positively influenced by litter mass and organic carbon. Soil fertility (0-10 cm upper layer) was higher in the planted stands than in the regenerating and secondary forests. The litter mass and its nutritional quality revealed differences in the capacity the various types of forest had in nutrient uptak and cycling. The mixed stand had an intermediate position in relation to the pure and natural forest stands. The litter decay rate was regulated by its quality. The results of this study indicate that the soil structure and fertility level under forest could be affected by litter nutritional quality and its decay rate. The mixed stand of forests species seemed to be the best plantation system, as it increases soil organic matter and fertility level and improve soil structure.

Propriedades químicas de uma Terra Roxa Estruturada influenciadas pela cobertura vegetal de inverno e pela adubação orgânica e mineral

This study was carried out to assess the influence of winter plant cover on the chemical soil properties in a Structured Terra Roxa soil in Santa Catarina, Brazil. The plant cover consisted of an association of black oats (Avena stirgosa Schreb) with pasture turnip (Raphanus sativus L.) and organic fertilization using poultry manure and mineral fertilization. Soil samples collected in August 1994 and January 1995, at depths of 0-10, 10-20 and 20-30 cm, were analyzed for an experiment initiated in 1990. The winter plant cover was efficient in maintaining nutrients (especially potassium) and the organic carbon levels within the limits of the plowable layer. The use of the organic fertilizer provided high nutrient accumulation in the soil, while the nutrients tended to be reduced by the organomineral and mineral fertilizers, mainly the levels of soil potassium.

Modelo Century de dinâmica da matéria orgânica do solo: equações e pressupostos

The modeling of biological processes has as objectives the planning of land use, setting environmental standards and estimating the actual and potential risks of the agricultural and environmental activities. Several models have been created in the last 25 years. Century is a mechanistic model that analyzes in long-term the dynamics of soil organic matter and of nutrients in soil-plant system in several agroecosystems. The soil organic matter submodel has the active (microbial biomass and products), slow (plant and microbial products that are physically protected or biologically resistant to decomposition) and passive (chemically recalcitrant or physically protected) pools with different decomposition rates. First-order equations are used to model all soil organic matter pools and soil moisture and temperature modifying decomposition rates. Turnover of active pool and formation of passive soil organic matter are mediated by sand and clay content, respectively. Plant residue is partitioned into pools dependent on the lignin and nitrogen content. Through the model, it can link organic matter at the fertility levels and the current and future management, optimizing the understanding of the transformations of the nutrients in soils of the several agroecosystems

FLUXO DIFUSIVO E BIODISPONIBILIDADE DE ZINCO, COBRE, FERRO E MANGANÊS NO SOLO: INFLUÊNCIA DA CALAGEM, TEXTURA DO SOLO E RESÍDUOS VEGETAIS

Em solos altamente intemperizados, o fluxo difusivo e o principal mecanismo de transporte de Zn, Cu, Fe e Mn ate a superficie das raizes das plantas. Praticas de manejo, como a calagem e a adicao de residuos vegetais ao solo, podem influir no fluxo difusivo e na disponibilidade desses micronutrientes cationicos. Neste sentido, o presente trabalho objetivou avaliar o fluxo difusivo e a biodisponibilidade de Zn, Cu, Fe e Mn, nas formas cationicas ou anionicas, em dois Latosssolos, sob influencia de doses de calcario e de residuos vegetais. Para tanto, os residuos vegetais, do feijao guandu ou do milheto, foram incorporados em amostra de um Latossolo textura media (LVA) e outro de textura argilosa (LV). Para avaliar o fluxo difusivo, utilizou-se resina de troca anionica (positivamente carregada) e de troca cationica (negativamente carregada) na forma de lâminas, incubadas no solo, em câmaras de difusao, durante quinze dias. Os resultados obtidos demonstraram que a calagem reduziu o fluxo difusivo dos micronutrientes, mas a incorporacao de residuos vegetais aos solos atuou inversamente, minimizando o efeito negativo da calagem na difusao. O Cu e o Fe foram transportados, predominantemente, na forma anionica, enquanto o Zn e o Mn, predominantemente, na forma cationica. A adicao de residuos vegetais tambem aumentou o pH dos solos e melhorou a absorcao dos micronutrientes pelas plantas de milho, principalmente, quando se incorporou residuo de milheto, no LVA, e de guandu, no LV.

Fluxo difusivo de micronutrientes catiônicos afetado pelo tipo, dose e época de incorporação de adubos verdes ao solo

Brazilian soils, especially in the Cerrado region, are highly weathered and poor in some cationic micronutrients in the soil solution. Diffusion is the main transport mechanism to the root surface. The adoption of management practices such as the use of green manures might favor the diffusive flux (DF) and availability of micronutrients to plants. The present experiment aimed to evaluate the effect of incorporation of two distinct green manures into a clayey Red Latosol (LV, Typic Haplustox) on the DF of the micronutrients Zn, Cu, Fe and Mn. For this purpose, two widely cultivated green manures: guandu bean (Cajanus cajan) or millet (Pennisetum americanum) were incorporated into the soil for different periods (0, 15, 25, 35, 45, and 55 days) and at variable doses (0, 9, 18, and 36 t ha-1, dry matter basis) before starting the evaluation of the DF. To evaluate the DF, two ion-exchange membranes (a positively-charged anionic and a negatively-charged cationic exchange resin) were incubated with the soil in diffusion chambers for 15 days. The obtained results demonstrated that there was an increment in the Cu and Fe DF with the increase in the doses of plant residues, particularly in the beginning of the incubation period. The results also showed a higher DF of these two micronutrients to the anionic resin compared with the cationic resin. This probably occurred because the Cu and Fe transport in the soil depends on the formation of organometallic complexes with net negative charge. The DF of Zn and Mn to occurred mainly toward the cationic resin. A longer incubation time favored the DF of Mn and Zn and reduced that of Cu and Fe.

Modelo fractal de substâncias húmicas

Fractal theoria application by determination of fractal dimension has been considered an alternative tool to explain the conformation of molecular aggregates. Its utilization in the study of humic substances (HS) aims the attempt to describe the limbed structure or the rugous and distorced surface of these substances. The presence of fractal models indicates that the system may be decomposed in parts, each part being a copy of the whole. In the experimental point of view the fractals models of natural systems may be measured through techniques as turbidimetry, x- ray and neutrons scattering. This paper seeks to facilitate the understanding on the application of the fractals in the conformational study of HS, supply information about fractal models foundation and use of the turbidimetry in the determination of fractal dimension.