Pedogênese e sequestro de carbono em planossolos ao longo de um gradiente pluviométrico na Província Borborema, Brasil

Abstract

Planosols are mineral soils with drainage restrictions. They have an abrupt change in texture, with the denser subsurface horizon due to the larger amount of clay. They are typical soils of the semiarid region of Brazil, however, few studies are performed for a better understanding of them. Most national works discuss physical, chemical, mineralogical and micromorphological aspects, and in the world, the discussion is related to its genesis, which is mostly based on the process of ferrolysis, however, other aspects deserve attention. A deeper understanding of the genesis of these soils, as well as the organic matter in it, will be of great importance for a scientific advance regarding the understanding of the evolution of these soils, their properties and their functions in the ecosystem. Therefore, the objective of this work is to characterize morphological, physical, chemical, microbiological, mineralogical and micromorphological planosols formed from the alteration of diverse metamorphic rocks over the Borborema Province, along a climossequence, aiming to better understand the genesis of these soils, which It is believed, for the development of research, that it is also associated with geogenic processes, and not exclusively pedogenic ones. For this, profiles were collected along the Borborema Province, regions inserted in the state of Pernambuco, with variable rainfall. Deformed and undeformed samples were collected for chemical, physical, mineralogical, petrographic, micromorphological, and microbiological analyzes, and an evaluation of the carbon stock in the area was also performed. The studied area, where these soils occur, has a considerable drought history and is subject to desertification processes if exposed to misuse. The chemical, physical and morphological characteristics led to the classification of the soils studied as Planosols, possibly formed by overlapping of material from adjacent areas (surface horizon), with concomitant clay formation in situ on the subsurface horizons, biotite and plagioclase being the most important. main primary minerals precursors of the secondary ones present in the clay, smectite and kaolinite fraction (main). Thus, ferrolysis is not the main process that promotes the formation of the soils studied, and the contribution of colluvium is a major factor. The studied Planossols presented relevant results regarding the stock of C, equating the total area occupied by these soils (130 million hectares) (9.5 Gt), to the stock of countries such as Chile and South Africa. mainly through organomineral interactions and nitrogen limitation in specific profile, in the subsurface horizons, position where the highest stock levels occur when observed the whole profile, on average 64% of accumulated C. With this, the Planosols, when evaluated worldwide become relevant for the storage of C. The evaluation of the properties of these soils contributes to the advancement of their knowledge in the caatinga ecosystem, which helps in studies on their potentialities and limitations. The better understanding about the carbon existing in these soils and its dynamics contributed to several aspects related to carbon storage in the semiarid, contributing to the protection of the area against possible degradation.