Compostos orgânicos, ciclos de umedecimento e secagem e a capacidade de suporte de carga de tecnossolos

Abstract

The Technosols derived from iron mining have limitations, among which is their structuring. The objective of this study was to investigate the effect of organic compounds (OCs) with different degrees of hydrophobicity and wetting and drying (WD) cycles on the structuring of Technosols formed after the collapse of the Fundão dam in Mariana (MG), using load- bearing capacity (LBC) as an indicator. Two experiments were conducted: (1) incubation of samples with OCs for 180, 365, and 547 days; and (2) analysis of the impact of 26, 52, and 78 WD cycles associated with the application of OCs. Both experiments followed a 3 x 2 x 4 x 3 factorial scheme, comprising 3 incubation periods (180, 365, and 547 days – exp-1) or 3 WD cycles (26, 52, and 78 – exp-2), 2 types of OCs (starch and stearic acid), 4 doses [0.0 (control); 2.5; 5.0 and 10.0 g kg−1], and 3 initial tensions for LBC measurement (-10, -100, and -1,500 kPa). The experimental designs were randomized block designs with 3 replications. After applying the OCs, the Technosol was placed in volumetric cylinders, set in trays, moistened to estimated field capacity (FC), and kept in a greenhouse. In exp-1, trays were sealed, while in exp-2, they remained open and were moistened weekly to FC. At the end of the incubation periods and WD cycles, the samples were saturated and equilibrated to tensions of -10, -100, and -1,500 kPa. They were then subjected to uniaxial compression testing to determine pre-consolidation pressures and develop LBC models. Additionally, total porosity (TP), microporosity (Mi), and macroporosity (Ma) were measured. The results indicated that in exp-1, OCs did not influence TP, Ma, or Mi of the Technosol. However, an effect on structuring was observed at 180 days, evidenced by increased LBC. It is possible to achieve increased LBC with a lower dose (2.5 g kg−1) of the hydrophobic OC, with a similar effect to that of a higher dose (10 g kg−1) of the hydrophilic OC. At 365 days, the hydrophilic OC showed an effect on Technosol structuring, acting as a modulator of LBC in relation to soil moisture. However, beyond 365 days, OCs did not affect the increase in LBC of the Technosol. In exp-2, the hydrophobic OC and WD cycles influenced TP and Mi. The hydrophobic OC contributed to the initial structuring of the Technosol, indicated by higher LBC values. This effect was achieved with a lower dose (2.5 g kg−1) and fewer WD cycles (26), or with higher doses (10.0 g kg−1) and more cycles (52 and 78). Conversely, the hydrophilic OC, when associated with a prolonged number of WD cycles (78), reduced the LBC of the Technosol. It is concluded that the application of OCs, especially hydrophobic ones at low doses and under fewer WD cycles, can aid in the structuring of Technosols derived from iron mining.