Mineralogia do saprolito e manejo de áreas no Núcleo de Desertificação de Irauçuba, Ceará: relações com a pedogênese de planossolos

Abstract

Food production and the consequent food security of vulnerable populations in arid and semiarid regions of underdeveloped countries in Asia, Africa and South America are limited by the climatic, environmental and socioeconomic characteristics of these regions. This worrying situation has been worsened by the variation of climate change in recent years. An example of this scenario can be observed in the most densely populated semiarid underdeveloped region in the world, located in northeastern Brazil, which faces serious problems in agricultural production due to limitations caused by climatic and soil conditions, resulting in the process of desertification in some places. However, restoration practices (e.g. fallowing) are promising to contain desertification and eventually improve soil functioning. However, the understanding of the effect of fallowing, the genesis and mineralogy of soils under desertification still remain poorly understood. Therefore, in this work we integrated pedology and management with the aim of expanding knowledge about the genesis of Planosols originating from a gneiss rock in a desertified area in the semiarid climate, in addition to verifying the effect of fallow on the weathering evolution of the profile in relation to a forested area and another overgrazed area. The experiment was conducted in a desertification center in the municipality of Irauçuba, in the semiarid region of Brazil, where we performed a morphological description of the soil profiles and collected undisturbed and disturbed samples of soil and saprolite, in three profiles, one located in an area under fallow practice for 20 years, another in an overgrazed area and the last in a forested area. Then, chemical and physical analyses were performed, in addition to mineralogical and micromorphological analyses for the purpose of classification and determination of the genesis and weathering evolution of the soil. The results indicated that fallow promoted considerable changes in the surface horizons, with an increase in organic matter and improvement of the soil structure. The granulometry reflected the influence of management on pedogenesis. Mineralogical analysis showed the predominance of aluminosilicate minerals and the presence of primary minerals, decreasing the importance of clay in the pedogenetic process. Micromorphology revealed the presence of biotite and feldspars in the installation process. However, the type of management did not significantly influence the weathering rates. Therefore, it is possible to conclude that the pedogenetic process is predominantly clay-based, with several biotite and feldspar minerals disintegrating, although a level of clay deposition was observed in the particles of the Bt horizon of all areas. Using weathering indices, it is shown that the type of management does not significantly influence the weathering rates of the areas.