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.

RESUMO Os solos construídos após a extração de carvão a céu aberto são compostos do solo superficial e, ou, do estéril de mineração. As propriedades químicas desses solos diferem das propriedades dos solos naturais, principalmente em razão do processo de sulfurização. O objetivo deste trabalho foi avaliar o potencial de acidificação da pirita e de contaminação com metais pesados ao longo de perfis de solos construídos após mineração de carvão, em áreas de diferentes idades, com e sem recuperação ambiental concomitante com a lavra. Foram selecionadas áreas mineradas denominadas de I e II, sem recuperação ambiental durante a lavra e compostas somente pelo estéril de mineração, representando as áreas mais antigas, e IV e VII, contendo topsoil e em alguns locais na camada de argila, constituindo as áreas mais jovens deste estudo. Foram coletadas amostras deformadas até 2 m de profundidade. Analisaram-se granulometria, densidade de partículas, pH em água, Ca, Mg, Al, K, Na, P, H+Al, potencial de acidificação, potencial de neutralização, potencial líquido, teor de C orgânico e condutividade elétrica no extrato da pasta saturada. Também foram extraídos os metais potencialmente biodisponíveis pela metodologia USEPA 3050B, cujos resultados foram comparados com os valores orientadores de prevenção e investigação para solos. Na análise univariada, foi aplicada a estatística descritiva e o teste de aderência de Kolmogorov-Smirnov. O grau de dispersão de cada variável foi avaliado qualitativamente e classificado como: baixo, moderado ou alto. A análise multivariada de componentes principais foi realizada para os solos construídos das áreas I, II, IV e VII; posteriormente, foram construídos biplots dos primeiros componentes principais. Os solos construídos das áreas mais antigas evidenciaram menores pHs e significativo potencial de acidificação. As camadas superficiais detopsoil, dos solos das áreas IV e VII, apesar de proporcionar condições químicas favoráveis ao estabelecimento de culturas agrícolas, não evitaram a formação de drenagem ácida em profundidade. O processo de sulfurização e sua relação com a liberação de metais foi melhor caracterizado pela análise de componentes principais realizada nas áreas IV e VII, em razão da correlação entre pH e saturação por bases nos estéreis só se expressar em saturações por bases acima de 40 %, não observada nos materiais dos estéreis das áreas I e II.

ABSTRACT Soils rebuilt after coal strip mining is composed of topsoil and, or, overburden, and their chemical properties differ from those of natural soils mainly due to the sulfurization process. The objective of this study was to evaluate the potential for acidification from sulfides and heavy metal contamination across profiles of soils rebuilt after coal mining, in areas of different ages, with and without concomitant environmental reclamation during mine operations. Mining areas of different ages were selected: areas I and II, without environmental reclamation during extraction and composed only from overburden, representing the oldest areas; and areas IV and VII, containing topsoil and, in some profiles, a clay layer (B and BC horizons from the natural soil) between the topsoil and the overburden, constituting the younger rebuilt mine soils. Soil pits were opened and disturbed samples were collected up to a depth of 2 m. Determinations were made of soil particle size, particle density, pH, Ca, Mg, Al, K, Na, P, H+Al, acidity potential, neutralization potential, net potential, organic C content, and electrical conductivity in saturated paste. In addition, potentially bioavailable metals were extracted by the USEPA 3050B method (Fe, Al, Mn, Ba, Cu, Zn, C, Cr, Co, Cd, Pb, Mo, As, and Se), and the results were compared to the guideline values of prevention and investigation for soils. In univariate analysis, descriptive statistics and the Kolmogorov-Smirnov test were applied. The degree of dispersion of each variable, expressed by the coefficient of variation, was qualitatively evaluated and classified as low, moderate, or high. Multivariate principal component analysis (PCA) was carried out for the constructed mine soils of areas I and II, and IV and VII, and then biplots were applied to the first principal components. The rebuilt mine soils from the oldest areas (I and II) showed lower pH (<3.2) and higher acidification potential. The topsoil and clay layers in areas IV and VII, in spite of providing favorable chemical conditions for surface vegetation, did not prevent acid mine drainage from developing in the subsurface. The sulfurization process and its relationship to release of metals was best characterized by principal component analysis performed in soils from areas IV and VII because the correlation between pH and base saturation in overburden layers is only expressed in base saturation above 40 %, which was not observed in rebuilt mine soils from areas I and II.