Desenvolvimento de Planossolos em distintas condições geoambientais e o efeito do pousio em áreas sob processo de desertificação

Abstract

The class of Planosols holds approximately 10.5% of total area of the Caatinga biome, which is among the most vulnerable to global climate change, in addition to suffering intense environmental degradation as to present areas in process of desertification. From the foregoing, this study had two objectives: 1- study Planosols and its morphological, chemical, physical and mineralogical characteristics under different rainfall rates in the state of Ceará and 2 evaluate the effect of the practice of 13 years in fallow attributes chemical, physical, mineralogical and organic soil carbon compartments, comparing the results of the practice of overgrazing in the area over the desertification process. For the first study, three areas were selected Planosols at different rates of rainfall, relief plane to gently rolling and even source material. Subsequently, trenches were opened for morphological description and collection of soil samples with disturbed and undisturbed soil structure which were taken to the laboratory for chemical, physical, mineralogical and semiquantification total element analysis. In the second study, both have been used two areas with 13 years of fallow and two areas where overgrazing, all located in the core Irauçuba desertification in the state of Ceará. These areas were opened four mintrincheiras to collect soil samples on the horizon A. The materials collected from disturbed and undisturbed soil structure were used for chemical, physical, mineralogical soil and physical fractionation of soil organic carbon. At the end of the analysis for the first goal, Planosols showed a distinct morphology, especially in relation to soil color on the horizon that darkened with increased rainfall, the thickness of horizons A and E which showed no direct relation to the increase in the rate precipitation and B horizon structure which is prismatic in more humid environment and in a columnar greater semiaridez condition. For the physical attributes in silt and silt relationship / clay indicate a more advanced stage of weathering with increasing rainfall. The clay dispersed in water increases and the degree of flocculation reduces with increased rainfall, favoring the process of Argilluviation, especially in Planosols with Solodic character. In chemical properties pH values in water, sum of bases (SB), capacity of cation exchange (CEC) and base saturation (V%) are not directly related to the increase in rainfall rate, even higher values It is scanned on the ground with greater semiaridez. Imperfect drainage condition, proven by the presence of mottled, plinthite and relief (the gently rolling plan), generally did not favor the efficient weathering action, allowing the mineralogical assembly did not suffer actual change in different conditions of precipitation essentially being formed by primary minerals: quartz, feldspar, mica, amphibole and secondary: kaolinite, smectite and vermiculite. For the second goal, the results show that the practice of fallow is protecting the soil against the advance of desertification, with better results in their physical and chemical attributes in relation to overgrazing. The highest total organic carbon values, particulate organic carbon and organic carbon associated to minerals were found in the fallow land. The areas where overgrazing are becoming arenizadas with the loss of fine sand, silt and clay and chemically poor. The management 13 years fallow did not alter the mineralogical assembly of sand, silt and clay compared to overgrazing. The smectite minerals, vermiculite and mica are the main responsible for the stabilization of organic carbon associated with minerals. The areas are still in the recovery process, it is important to maintain the monitoring of soil attributes to understand the dynamics of the recovery of areas in process of desertification.