Geoambientes e solos no Pantanal do Abobral, Mato Grosso do Sul, Brasil.

Abstract

The Pantanal basin is seasonally flooded in different degrees in space and time, overflowing most part of the lowland and forming distinct landscape units or geo-environments. The Abobral Pantanal is one of the Pantanal sub-regions. This study aimed to classify and report soil physic-chemical characteristics and evaluate the soil-plant relations. We subdivided the landscape using hydromorphism, phytophysiognomies, relief, and soil conditions. The Abobral Pantanal was stratified in four geo-environments: Cordilheiras with semi deciduous forest over Chernozems with petrocalcic horizon; Corixo with flooded forest over Planosols with vertic character; Campo com Cambará over Planosols with gley character; and Lagoa Intermitente over eutrophic Planosols. At Cordilheira geo-environment, a non-flooded area, occurred snail shells buried in the soil at mean depth 55-80 cm, inducing occurrence of base rich Chernozems. At Cordilheiras there is occurrance of calcite, mica, smectites and albite. The high pH, the drain obstruction, and abundant occurrance of Ca and Mg in soluble forms in the soil allows high stability to the snail shells. At the seasonally flooded geo-environments the planic B horizon supports the maintenance of a higher water table. At these seasonally flooded geo-environments occurs micas, smectites, calcite, microcline, caulinite and quartz. At Cordilheiras, the snail shells dissolution above petrocalcic horizons are not the main ion source for petrocalcic horizon formation. The Mg soil richness indicates other non-biogenic carbonate source. The calcareous higher lands around Pantanal are likely responsibles for enrich the water flood at Abobral Pantanal. Sediments dating above and below the petrocalcic horizon points to 2500 BP the most likely time of the petrocalcic formation. At that time, the Pantanal basin were probably drier with a lower drainage, which would favor a cemented strata formation. Snail shells dating indicates mean age of 1700 BP, its deposition it is not considered anthropic. Petrocalcic horizon and Chernozems formations were not simultaneously. After the petrocalcic resposible event there was younger materials deposition, about 600 BP. Petrocalcic horizon partial degradation, allied to soil bioturbation originated Chernozems.