Dinâmica Espaço Temporal do Carbono do Solo na Bacia do Arroio Piraizinho em Bagé, RS

• Autor(a) principal: Santos, Fioravante Jaekel dos
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: Repositório Institucional da UFPel - Guaiaca
• Texto Completo: http://repositorio.ufpel.edu.br/handle/ri/2463
• topic: Cenários de uso do solo; Century v4.0; Geotecnologias; Bioma pampa; Modelagem espacial; Soil carbon; Century v4.0; Geographical information system; Spatial modeling; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA

Agricultural practices, among others, contribute to reduce the environment quality, through the unbalance between the CO2 fixation and emission to the atmosphere. The importance of soil carbon stocking surpasses the matter of carbon sequestration in itself, since the kinds of soil management that rise their stocks in soils also have a positive effect on their quality as a whole. The soil carbon stocks evolution in a specific site as a function of its past and future uses can be studied through mathematical models as Century. The linking of this model with Remote Sensing and Geographical Information Systems makes it possible to analyze and model the carbon stocks spatial distribution and variability in a certain geographic area. In this study a catchment basin (Piraizinho stream, Rio Grande do Sul State) located in the Brazilian Pampas, traditionally exploited with cattle grazing on native grassland, was selected to analyze and model the soil carbon stocks changes due to other land uses that have arisen in the region in the last twenty years. In order to achieve this, a semi-detailed soil survey was performed, followed by a spatial and temporal analysis of the land uses, based on aerial photographs and satellite images as well as field survey and interviews with landowners and technicians. To establish the parameters and validate the model, a soil sampling was performed based on the soil units and different types of land uses. The data spatial modeling was done on a GIS base using the soil units map and relief in a such a way as to point model the carbon stock through the erosion variable, where to each pixel it was assigned a soil loss using the USLE. Regosols (RReh and RLd units), Acrisols (PVd unit), Luvisols (TXo1, TXo2, TXp, TCo units), Chernozems (MEo unit), Vertisols (VEo unit), and Gleysols (GMve unit) were mapped in an average gently rolling landscape. In 1967 98,75% of the area was used solely by extensive cattle grazing on native grassland, by 2009 this was reduced to 82,67%, due to rice and soybeans crops as well as eucalyptus and acacia foresting. The topsoil carbon stocks varied as a function of the soil units and kinds of use. The largest carbon stocks under traditional grazing simulated to the year 1990 were found on soil units MEo (89,04 Mg ha-1 C) and TCo (79,87 Mg ha-1 C), while soil units RLd (27,48 Mg ha-1 C) and PVd (41,73 Mg ha-1 C) were responsible for the lowest stocks. The simulations also indicate that the no till system with soybeans in summer and rye in winter is not able to maintain the carbon stocks in any of the soil units modeled. The continuous use of this system for 50 years can lead to the consumption of 35% of the carbon stocked in the topsoils (without considering VEo and GMve soil units that were not simulated). The Voisin rational grazing system, that has been adopted by 45 years in a property in the area, showed a higher potential than the traditional system without fire to accumulate carbon in the soils.