Luiz Eduardo Ferreira Fontes

Atributos físicos do solo e distribuição do sistema radicular de citros como indicadores de horizontes coesos em dois solos de tabuleiros costeiros do estado da Bahia

The physical characterization of two typical Coastal Tableland soils (Yellow Latosol-YL and Gray Argisol-GL) of the State of Bahia, Brazil, was carried out in 2001 and the citrus root system in such soils was evaluated in order to determine attributes that best identify the cohesive layer. The first four horizons in each soil were sampled for analysis of particle size distribution, soil bulk density, total porosity, macroporosity, microporosity, and saturated hydraulic conductivity. Soil resistance to penetration and critical humidity of soil resistance to penetration were determined. Citrus root samples were collected in the same horizons and the results were expressed in cm cm-³ of soil. The citrus root system density reduced abruptly in the AB, Bw1, BA, and Bt1 horizons, and this was associated to soil cohesion. The best attribute to identify cohesion was soil resistance to penetration, which should be evaluated at soil humidity below the critical level to express cohesion. Saturated hydraulic conductivity was another attribute that proved appropriate to evaluate soil cohesion. It can be substituted by macroporosity, which is equally important to identify cohesion, with less variability besides being easier to measure than saturated hydraulic conductivity. Soil bulk density can be considered an attribute to evaluate the presence of cohesive horizons, but its use is limited mainly by the interference of particle size in its determination. The recommended indicators allow the detection of the presence of cohesive layers, orienting additional soil management practices to overcome the problems that such soils present for deep root growth.

ESTOQUE DE CARBONO DO SOLO SOB PASTAGEM EM ÁREA DE TABULEIRO COSTEIRO NO SUL DA BAHIA

The replacement of forest environments by pastures leads to fundamental alterations in soil carbon stocks and consequently in the global cycle of this element. This study was conducted in the municipality of Itabela, Bahia, and the objective was to evaluate carbon stocks in soils of a natural forest in comparison to degraded and productive pastures with different usage periods. For this purpose, remnants of the Atlantic Forest, productive pastures after different periods of use (2, 9 and 18 years) and an ill-managed pasture (18 years) were selected. All areas were located on a flat terrain of the same soil class (Typic Paleudult). In each area three plots were established and used for soil sampling and subsequent carbon analyses. Results showed no significant difference in soil carbon stocks in the forest and degraded or productive pastures with different use periods and soil layers. Moreover, it was observed that after 28 years of usage an average of the 62 % of organic carbon found in well and ill- managed pastures was still derived from the original forest soil organic matter.

Modificações causadas pelo uso e a formação de camadas compactadas e, ou, adensadas em um latossolo vermelho-escuro textura média, na região do cerrado

O objetivo deste trabalho foi avaliar as modificacoes causadas pelos diferentes usos em atributos de um Latossolo de textura media e a influencia destas na formacao de camadas compactadas e, ou, adensadas de subsuperficie, sob diferentes usos agricolas, na regiao do cerrado. Para tanto, em abril de 1994, nos municipios de Uberlândia e Monte Alegre de Minas, foram selecionados seis locais onde o solo foi amostrado em trincheiras: CC (Fazenda Canada, vegetacao de cerrado); CP (Fazenda Canada, cultivo com uso de pivo central); GC (Fazenda Gaia, vegetacao de cerrado); GPa (Fazenda Gaia, pastagem); GP1 e GP2 (Fazenda Gaia, cultivo com uso de pivo central). O solo foi classificado como Latossolo Vermelho-Escuro, textura media e apresentava camadas compactadas e, ou, adensadas em subsuperficie, incluindo as areas sob vegetacao de cerrado, variando apenas o valor da densidade do solo e a profundidade em que a camada aparece. O cultivo provocou modificacoes em relacao a presenca do cerrado. A area sob pastagem, exceto por um aumento superficial na resistencia a penetracao, apresentou comportamento semelhante ao das areas sob cerrado. O aumento da densidade nas camadas subsuperficiais deveu-se, possivelmente, ao aumento da argila dispersa em agua nas areas cultivadas. O aumento da argila dispersa em agua ocorreu em decorrencia de diversos fatores, tais como: reducao do carbono orgânico, calagem e aumento do PCZ. Ocorreu correlacao positiva e significativa entre o teor de SiO2 e a percentagem de argila dispersa em agua e, consequentemente, com a formacao de camadas compactadas e, ou, adensadas, no solo estudado, sob diferentes usos.

ATRIBUTOS MICROMORFOLÓGICOS DE SOLOS DO PROJETO JAÍBA, NORTE DE MINAS GERAIS

Undisturbed samples of representative horizons of soils from Jaiba Project, northern Minas Gerais, Brazil, and compacted and non-compacted layers of soils under intensive use were collected and micromorphologically analyzed to obtain more information on their evolution degree and also to evaluate the soil alterations caused by agricultural use. Four soils derived from limestone (P1 to P4) and one originated from detritic sediments (P5) were studied, as well as layers with and without indication of compaction. The micromorphological study revelead that the soils have very distinct and variable characteristics as a function of their classes and parent materials. The Cambisol (Inceptisol) originated from limestone has as a remarkable characteristic the vertical flux of silica and clay, without, however, characterizing textural (similar to argillic) horizon and a higher development of blocky structure. The Cambisol derived from detritic sediments presents a lateral flow of clay, a remarkable presence of iron diffusion skins and a less developed tending to granular structure. The Dark-Red Podzolic soil (Alfisol) showed blocky structure and the presence of deposition skins, many of these features being incorporated by the s-matrix, possibly an indication of transition to Latosol (Oxisol). The Latosols present granular structure, but this is much less developed than the corresponding one observed for the gibbsitic Latosols already analyzed in the country, what may indicate a smaller degree of evolution of these soils. The faunal activity seems to be the main responsible agent for the development of the Podzolic and Latosols microstructures. As for compaction, the micromorphological studies revealed differences in the plasm organization and in the form of pores when compacted and non-compacted layers were compared. In general, the plasm of the compacted layers is denser and the pores are altered as a function of the physical effort imposed to the soils.

Química e mineralogia de solos derivados de rochas do Grupo Bambuí no norte de Minas Gerais

Representative soil profiles from the Agroindustrial District of Jaiba in northern Minas Gerais State, Brazil, were morphologically described, sampled and chemically, physically and mineralogically analyzed, to obtain data which could contribute to their improved utilization. Although the parent material was almost the same (Bambui group limestone), and the apparent physiographical homogeneity (flat relief and deciduous forest), the soils presented great morphological, chemical and mineralogical diversity. From a mineralogical standpoint, illite and kaolinite are common minerals, the latter found even in Vertisols and Rendzinas, which are soils with substantial amounts of free carbonates. The presence of smectite in Vertisols, Rendzinas and Cambisols of high activity clay, indicates that rain shortage, richness of parent material and its shallow depth on a flat topography, hinder the escape of silica and bases from the system, favoring the smectite formation. The mineralogical composition, together with the climatic seasonal variability, appears to be responsible for the accentuated cracking of these soils in the dry season. The soils present various colors: red, and red-yellow, due to the presence of hematite and goethite, mainly in Oxisols on slightly elevated landscape positions, therefore with better drainage; yellow and yellowish-brown colors, normally in the more depressed areas, with worse drainage, associated with the shallow depth and high density of the parent material, favoring the genesis of goethite and leading to significant amounts of manganese-iron concretions, with occurrence of Cambisols with high (Ta) and low activity (Tb) clays, Vertisols or soils with vertic characteristics, also brownish, and Rendzinas. The low Feo/Fed ratio (iron oxalate/iron dithionite) revealed predominance of more crystalline iron oxides. The eutrophic and epieutrophic soils (dystrophic or allic) with low Na contents and a dominantly flat and gentle undulated relief confirm the great agricultural potential of the area, especially under irrigation. However, the soil chemical, physical and mineralogical characteristics diversity indicates variable soil beahavior depending on land use, suggesting the adoption of differential soil management practices.