Resumo O objetivo deste trabalho foi avaliar a condição física e a potencialidade de uso agrícola de um solo construído após mineração com carvão, além do desenvolvimento radicular de gramíneas tropicais nesse solo, tendo-se considerado diferentes períodos de revegetação. O solo foi construído no início de 2003, e o experimento instalado em novembro/dezembro de 2007. A condição física do solo construído foi avaliada nas parcelas ocupadas por gramíneas perenes, como Urochloa humidicola, Panicum maximum e U. brizantha. Em julho de 2012, foram coletadas amostras de solo com estrutura preservada e não preservada para a determinação dos atributos físico-químicos, nas camadas de 0,00-0,10, 0,10-0,20 e 0,20-0,30 m. Monólitos de solo foram coletados para caracterização do sistema radicular das diferentes gramíneas. Após 58 meses de revegetação, a condição física do solo construído ainda é inadequada ao uso agrícola que envolva práticas mais intensivas de manejo de solo. Entre as camadas avaliadas, somente a de 0,00-0,10 m fornece condições para que o solo cumpra suas funções no ecossistema. Urochloa brizantha mostra-se mais promissora para a recuperação da estrutura do solo na camada de 0,00-0,10 m, e a densidade radicular foi o atributo mais sensível para a diferenciação do desenvolvimento potencial das diferentes espécies nesta camada.

Abstract The objective of this work was to evaluate the root development of the physical condition and the potential of agricultural use of a constructed minesoil after coal mining, besides the root development of tropical grasses in this soil, considering different revegetation periods. The soil was constructed in early 2003, and the experiment was installed in November/December 2007. Soil physical condition was evaluated in plots vegetated with perennial grasses such as Urochloa humidicola, Panicum maximum, and U. brizantha. In July 2012, disturbed and undisturbed soil samples were taken for determining physical and chemical attributes in the 0.00-0.10, 0.10-0.20, and 0.20-0.30-m soil layers. Soil monoliths were collected for characterizing the root system. After 58 months of revegetation, the physical condition of the constructed minesoil is still inadequate to an agricultural use that requires intensive soil management. Among the evaluated layers, only the 0.00-0.10-m layer provides conditions for the soil to function properly in the ecosystem. Urochloa brizantha was more promising for the recovery of soil structure in the 0.00-0.10-m soil layer, and root density was the most sensitive attribute to distinguish the potential development of the different species in this layer.

ABSTRACT: Studies addressing the potential of grass roots in improving the structural quality of constructed minesoils are not frequent in the literature, although they are essential for understanding the re-establishment of soil functions in the environment. The objective of this study was to quantify the root attributes of the species Urochloa humidicola, Panicum maximum, and Urochloa brizantha and relate them to the physical properties of a constructed minesoil in reclamation of an area degraded by coal mining. The study was performed in a field experiment in a coal mining area located in southern Brazil. Soil samples were collected, five years after experiment installation, to determine bulk density, macroporosity, distribution of water stable aggregates expressed in different size classes, mean weight diameter of water stable aggregates, and organic carbon content, as well as for chemical characterization. Root sampling was performed by the monolith method to a depth of 0.30 m. Results confirm the hypothesis that the root system of the perennial grasses studied positively contributes to recovery of the constructed minesoil in the 0.00-0.10 m layer after 58 months of revegetation. The higher percentage of large aggregates, higher bulk density, and lower macroporosity in the subsurface indicate the presence of degraded layers, negatively influencing the development of the grass root system. Urochloa brizantha exhibited the largest root matter in the surface layer, influencing the breakdown of the large and cohesive aggregates, transforming them into smaller crumbly aggregates. In the 0.10-0.20 m layer, Urochloa humidicola showed greater volume and root length in relation to other species; nevertheless, changes in soil physical properties were not observed, showing that the time span of the root growth of the species was not sufficient to provide improvements in the subsurface layers.