Atributos físicos, químicos e biológicos do rejeito de mineração oriundo da Barragem de Fundão modificados por sistema de consórcio e plantio de Enterolobium contortisiliquum

Abstract

The objective of this study was to evaluate the changes in the chemical, physical and biochemical properties of the Tecnosolo formed from the tailings deposited on the banks of the Rio Doce River Basin, after the Fundão dam rupture, and to determine which proposed revegetation systems promoted the best conditions for the rehabilitation of the impacted areas. The experiment was conducted in a greenhouse using iron mining tailings collected on the banks of the Gualáxo do Norte river, two years after the Fundão dam rupture in Mariana, Minas Gerais - Brazil. The proposed revegetation systems are intended to initiate the rehabilitation process with herbaceous plants and, subsequently, the establishment of native tree. To this end, the study was divided into two phases. Initially, the treatments were distributed in a randomized block design in a 5x2 factorial scheme, with three replications. The treatments consisted of precultivation systems with intercropped herbaceous plants: Urochloa ruziziensis single (RS); U. ruziziensis intercropped with Crotalária spectabilis (R+C); U. ruziziensis intercropped with Guizotia abyssinica (R+G) and U. ruziziensis intercropped with C. spectabilis and G. abyssinica (R+C+G) and two arbuscular mycorrhizal fungus (AMF) inoculation conditions, with and without inoculation, lasting 100 days. Simultaneously, another 5 replications of each treatment were established, however, without the inoculation factor, besides a control treatment containing only technosol, without the preculture of the herbaceous plants. These treatments comprised the second phase of the study, in which 100 days after germination, the herbaceous plants were cut at the height of the collection, crushed (5 cm) and placed over their respective pots. The experimental design was a randomized block design with five replications. The treatments consisted of the tree Enterolobium contortisiliquum established on the cover of herbaceous plants: U. ruziziensis single (Ruz/E); U. ruziziensis + C. spectabilis (R+C/E); U. ruziziensis + G. abyssinica (R+G/E), U. ruziziensis + C. spectabilis + G. abyssinica (R+C+G/E) and Technosol without plants (Rej/E). This phase began after the tree was established and lasted 120 days. The inoculation with AMF did not influence the shoot dry matter production or the accumulation of elements in the herbaceous plants cultivated in Tecnosolo. The greater diversity of herbaceous plants (R+C+G) proved to be efficient in the production of phytomass and in the initial stabilization of the technosol, which may be a viable alternative for the rehabilitation process. Also, the accumulation of chemical elements was higher in R+C+G cultivation, indicating the potential of these species in the extraction of the chemical elements contained in the Tecnosolo. At the end of the second phase of the study, it was observed that the system composed by the greater plant diversity (R+C+G/E) favored the absorption of elements in the E. contortisiliquum tree shoot, while in the R+C/E and, the tree was contrary to the evaluated production indexes. The E. contortisiliquum showed to be efficient in the rehabilitation of the technosol by absorbing metals in its aerial part, demonstrating that this tree species has potential to be used in the phytostabilization of these areas. Still, at the end of both phases, it was evaluated the physical, chemical and biochemical attributes of Tecnosolo, it can be observed that the rehabilitation system composed by Ruz/E and R+C+G/E contribute to the improvement of the attributes. Technosol, while the R+C/E system is contrary to improving the development of physical attributes.