Mineralogia da fração argila de um argissolo submetido ao sistema de plantio direto por vinte e quatro anos

Abstract

In the last decades, it has been more intensive the development and improvement of techniques which aim to provide the sustainability of productive farming systems, while increasing their yields. In this scenario, is included the no-tillage system (SPD), which continuous use, observing the practices recommended by the management system besides the soil preservation practices, has been showed noticeable effects on the improvement of soil physical, biological and, possibly, mineralogical attributes. The main goal of this work was to evaluate the no-tillage system effects on the soil Fe oxides and kaolinite (Kt), resulted from 24 years using the following management systems: i) absence of agricultural cultivation, ii) SPD without grazing, iii) SPD with grazing simulation and iiv) native pasture – control. The effects evaluation was made through a chemical attributes analysis, use of x-ray diffraction and thermal analysis techniques, applied on soil layers of 0-5cm and 5-10cm in a Typic Paleudalf of the Central Depression region of Rio Grande do Sul. Although some physical and chemical attributes were altered, through the techniques used it was not possible to show treatments effects on Fe oxides, Kt and 2: 1 amounts mineralogy changes after 24 years of implantation on the Paleudalf. The Fe oxides abundance indicated the predominance of crystalline forms over the low crystallinity ones in all treatments and in the control, which did not have differences between the two layers. The isomorphic substitutions of Fe for were more significant in the less crystalline oxides. The Fe oxides crystallography referred to the greater occurrence of goethite (Gt) in comparison to the hematite (Hm), corroborating the results identified in the reflexes of the x-ray diffractograms. The isomorphic substitution (SI) was more expressive in Gt, and the predominance of widths at higher half (LMA) in these oxides indicated their lower degree of crystallinity compared to Hm. The average crystal diameters (DMC) indicated higher crystal occurrence in Hm, but with lower abundance compared to Gt. The higher values of the Gt / Gt + Hm ratio in the more superficial portion indicate there is a Gt formation promotion at this depth. It was verified a disordered Kt expressiveness in relation to more crystalline forms. In the two layers there were no distinctions between treatments with respect to the development of Kt crystals. The SC treatment showed the soil losses effect on Kt expressiveness, Kt IC and 2: 1 minerals.