Estabilidade de agregados e matéria orgânica em solos de elevado teor de areia na Depressão Central Sul-Riograndense frente ao aumento de temperaturas

Abstract

In view of the natural susceptibility to erosion of the predominant soils in the region of the Sul-riograndense Peripheral Depression, this study aimed to investigate the relationships between the increase in temperatures associated with climate change and the possible intensification of erosion processes on these soils in order to contribute and better understand the prognosis of this condition. Based on the relationship between organic matter and aggregate stability, with the latter as a parameter of erodibility, this study proceeded with expeditious preliminary evaluations of three samples and incubations of two samples, predominantly sandy and clayey, respectively. In the preliminary evaluations, the samples were placed in different environmental conditions such as a greenhouse and a refrigerator for approximately 70 days, to later apply the methodological evaluation of the stability index of aggregates in water and the content of organic matter, through the determination of the total carbon of the soil by ignition, before and after treatment. With this, the proposed methodology was tested and relevant assertions were contributed. Subsequently, the heat treatment itself began, the incubation, proposed to simulate the action of the conditions of rising temperatures associated with climate changes on the samples in a thermal box built specifically for the treatment. With this, an attempt was made to simulate a table of daily temperature cycles of a degraded soil in the southwest of Rio Grande do Sul during the month of January at a depth of 10 cm, oscillating between 28°C to 35°C, assuming that this would be a table of high temperatures to test the hypothesis that, under such climatic conditions, organic matter, the main cementing agent of the structure of sandy soils, would be affected and so would the susceptibility to erosion. Thus, analyzes of organic matter and aggregate stability were performed immediately after sample collection and throughout the incubation heat treatment every two weeks, lasting approximately 120 days. For reasons of apparent discrepancies in the organic matter results, the heat treatment test was repeated a second time. However, these results reappeared even in the second experiment and were assumed to be characteristic of this evaluation. Thus, it can be concluded from preliminary assessments that environmental restrictions on microbial action on organic matter, such as droughts, may not intensify erosion processes with regard to stability assessments of aggregates in water. And, from the incubations, it can be concluded that the passage of time under thermal action considerably increased the susceptibility to erosion in the sandy samples given their dependence on organic matter as a structural factor. The clayey samples, structurally governed by the electrostatic principles of clay dispersion, are not as vulnerable to heat treatment, although they show a decrease in the stability of aggregates at the end of the treatments. Thus, the proposed study concludes that the increase in temperatures, along with moisture, intensifies the erosive processes mainly in soils with sandy granulometry and that the replacement and maintenance of organic matter levels in the soil are fundamental to avoid this situation capable of leading to the destabilization of the landscape.