A influência do pH na gênese de horizonte com caráter coeso

Abstract

In Tabuleiros Costeiros, which extends from Southeast to Northern Brazil, the soils were developed from sediments of the Formação Barreiras and can present horizons with cohesive character, which are dense. Thus, this work was developed based on the hypothesis that soil pH may contribute to the formation of cohesive horizons by influencing clay dispersion and, consequently, densification. The general objective of this study was to evaluate the pH range that can contribute to clay dispersion, favoring clay tilting and densification of horizons of soils of Tabuleiros Costeiros, seeking specifically (i) to determine the physical parameters, related to the cohesive character, which were influenced by soil pH and (ii) to evaluate the influence of pH on clay dispersion in soils with different clay concentrations. The experiment was conducted with material collected from the B horizons, with cohesive character - CCC and without cohesive character - SCC, of soils in areas with lower clay content (~200 g kg-1 / Pacajus-CE) and higher clay content (~300 g kg-1 / Fortaleza-CE). The samples were collected in polyvinyl chloride (PVC) tubes, 7 cm high and 5 cm in diameter, which were submitted to nine cycles of percolation with solutions with the following pH values: 4,25; 4,75; 5,25; 5,75 and 6,25. After the cycles, analyses of water dispersed clay (WDA), soil density (SD) and soil resistance to penetration (Rp) were performed, to evaluate if there was any influence on the degree of soil densification. Other physical and chemical analyses were performed to complement the results regarding clay translocation due to pH influence. The factorial scheme was 2 x 2 x 5, where the first factor corresponds to the two soils (with more and with less clay), the second factor corresponds to the Bt horizons with cohesive character and without cohesive character and the third factor corresponds to the five pH values, with five repetitions. We conclude that: (i) the hypothesis was confirmed for the Fortaleza horizon - SCC (FSC) and refuted for the Pacajus-SCC (PSC); (ii) some variables identifying the cohesive character were sensitive to the treatment with pH solutions, as Ds and Rp in the (PSC) and there was no translocation of the water dispersed clay (WDA) by the influence of pH that characterizes the horizon as cohesive. The treatment with the solutions (different pH) favored the dispersion of clay in the FSC horizon; (iii) in the Fortaleza - CCC (FCC) horizon the less acidic solutions contributed to increased densification; in the Pacajus - CCC (PCC) horizon the ADA contents were not altered, but it was observed that fine material was lost during the cycles of percolating solutions; (iv) the physical parameters influenced by the pH of the percolating solutions were Rp, Ds, total clay, ADA, flocculation degree and total porosity.