Caracterização de luvissolos, neossolos regolíticos e planossolos ao longo de um gradiente pluviométrico no semiárido brasileiro

• Autor(a) principal: Saraiva, Sebastiana Maely
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações da UFPB
• Texto Completo: https://repositorio.ufpb.br/jspui/handle/123456789/25535
• topic: Mineralogia; Classificação de solo; Pedogênese; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA

The soil is a natural resource of great importance to mankind and as such has been extensively studied in several aspects. In regions with limitations imposed by climatic conditions, such as in the arid and semi-arid regions, soils are poorly developed from the pedogenetic point of view and are generally shallow. Little is known about the soils of the semi-arid region of Brazil, that require the generation of information about its fertility, genesis and mineralogy, among other aspects. The objective of this work was to evaluate the influence of the rainfall gradient on the formation and development of soils of three classes: Luvisols, Regolithic Neosols and Planosols, in different soil forming environments, in the state of Paraíba, studying their morphological, physical, chemical and mineralogical attributes. For this purpose, the semi-arid region of Paraiba was subdivided into three climatic subtypes according to the annual average rainfall: very dry (<400 mm), dry (> 400 and <600 mm) and sub-humid (> 600 mm) where nine trenches were open for collection and description of the profiles. Soils were characterized as to their physical properties (particle size distribution, clay dispersed in water, soil and particle density, flocculation degree and porosity) and chemical (Ca, Mg, Na and K, Al, H + Al, COT, P and pH). To identify the mineralogical composition of each fraction by X-ray diffractometry (XRD), the soil fractions were separated by wet sieving from three horizons of each profile. Afterwards, the necessary treatments were applied for the removal of the cementing agents and saturation with Mg and K. The sand and silt fractions were submitted to XRD in the form of non-oriented powder and the clay in the form of oriented slides. In Luvisols we noticed a clear influence of the climate on the pedogenetic processes that resulte in an increase in soil depth with increasing rainfall. The influence of rainfall on the physical attributes was noticeable in the clay contents; regarding fertility, there was no clear influence of climate on the availability of nutrients; The mineralogy of the Luvisol clay fraction is predominantly composed of secondary minerals. In the Regolithic Neosols xvii rainfall had no effect in the differentiation of their horizons and profile depth, since their profiles were very similar morphologically; the soils clay content increased gradually from the very dry condition to the dry and sub-humid condition, showing the influence of rainfall that also reflected in the fertility of the Neosols; sodium content higher than 6% in the Cn1 and Cn2 horizons of the Regolithic Neosol in the sub-humid condition suggest the occurrence of a new class to be inserted in the Brazilian Soil Classification System - Solodic Dysbolic Regolithic Neosol. In the Planosols it was not possible to observe the relationship between soil depth and the climatic conditions, because they are soils formed from rocks that are more resistant to weathering; Apparently there was little influence of climate on depth, being shallower the soil of the dry condition and deeper that one of the very dry condition; On the other hand, rainfall was important in the formation of diagnostic horizons (Bt), with clay content proportional to rainfall; the Planosols presented high levels of exchangeable bases and as for fertility, they showed the same tendency of the Luvisols, evidencing base leaching in the sub - humid climate condition. In some horizons of the studied soils high levels of salinity were verified. The coarser fraction of the soil consists of minerals more resistant to weathering. In all studied horizons, quartz and feldspar occur, as was also observed in the silt fraction, which expresses the low degree of pedogenetic development of these soils. The mineralogical composition of the clay fraction of the studied soils is similar, with a predominance of secondary minerals such as smectite, ilite and kaolinite in the Luvisols and quartz and feldspar in the Regolithic Neosols and Planosols.