Soil aggregation and root growth of perennial grasses in a constructed clay minesoil

Studying constructed soils (anthropogenic) in mined areas provides an opportunity to expand the existing knowledge about the formation and stabilization of aggregates, due to the magnitude of ecosystem disruption, that creates a “zero time” scenario. The aim of this study was to evaluate the relationship between the aggregation and the root growth of perennial grasses 103 months after the reconstruction of a constructed minesoil, in a coal mining area located in Candiota/Rio Grande do Sul State, Brazil. The evaluated plant species were Hemarthria altissima, Paspalum notatum cv. Pensacola, Cynodon dactylon cv. Tifton, and Urochloa brizantha. The grass roots promoted the recovery of the soil physical condition in the 0.00-0.10 m layer, with a decrease in dry bulk density and an increase in soil macroporosity related to the formation of new aggregates. The decrease in root development of all species below 0.10 m depth is the result of the restrictive soil physical conditions, with high bulk density and low macroporosity related to aggregates formed originally by compression. The results of root and soil attributes found in this study suggest a different soil-aggregation hierarchy in compacted constructed minesoils, where first a disintegration occurs of large cohesive aggregates formed by compression followed by a re-aggregation process, with sequential re-formation and stabilization of aggregates. The Urochloa brizantha showed a greater root density, volume, length and area, thus presenting a greater potential to recover the physical attributes of the degraded areas, especially those in the compacted layer below 0.10 m depth. The recommendation of this and other species in the reclamation of constructed soils after coal mining should take into account the thickness of the topsoil layer because the roots of these species can grow into the overburden layers and thus accelerate the sulfurization process. The recovery of physical attributes of the constructed minesoil, especially below the 0.00-0.10 m layer, is a slow process, possibly due to the low accumulation rates of organic carbon in this layer.