Perennial grasses for recovery of the aggregation capacity of a reconstructed soil in a coal mining area in southern Brazil

Abstract

The construction of a soil after surface coal mining involves heavy machinery traffic during the topographic regeneration of the area, resulting in compaction of the relocated soil layers. This leads to problems with water infiltration and redistribution along the new profile, causing water erosion and consequently hampering the revegetation of the reconstructed soil. The planting of species useful in the process of soil decompaction is a promising strategy for the recovery of the soil structural quality. This study investigated the influence of different perennial grasses on the recovery of reconstructed soil aggregation in a coal mining area of the Companhia Riograndense de Mineração, located in Candiota-RS, which were planted in September/October 2007. The treatments consisted of planting: T1- Cynodon dactylon cv vaquero; T2 - Urochloa brizantha; T3 - Panicum maximun; T4 - Urochloa humidicola; T5 - Hemarthria altissima; T6 - Cynodon dactylon cv tifton 85. Bare reconstructed soil, adjacent to the experimental area, was used as control treatment (T7) and natural soil adjacent to the mining area covered with native vegetation was used as reference area (T8). Disturbed and undisturbed soil samples were collected in October/2009 (layers 0.00-0.05 and 0.10-0.15 m) to determine the percentage of macro- and microaggregates, mean weight diameter (MWD) of aggregates, organic matter content, bulk density, and macro- and microporosity. The lower values of macroaggregates and MWD in the surface than in the subsurface layer of the reconstructed soil resulted from the high degree of compaction caused by the traffic of heavy machinery on the clay material. After 24 months, all experimental grass treatments showed improvements in soil aggregation compared to the bare reconstructed soil (control), mainly in the 0.00-0.05 m layer, particularly in the two Urochloa treatments (T2 and T4) and Hemarthria altissima (T5). However, the great differences between the treatments with grasses and natural soil (reference) indicate that the recovery of the pre-mining soil structure could take decades.

Reclamation of a Degraded Coal-Mining Area with Perennial Cover Crops

“…In the constructed minesoil, the aggregation results are likely also derived from soil particle cohesion, due to intense machine traffic carried out in soil construction, as already discussed by Stumpf et al (2014). This type of condition was also reported in minesoils by Sencindiver and Ammons (2000) and in agricultural soils by Rev Bras Cienc Solo 2016;40:e0150482 Voorhees (1983), Carpenedo and Mielniczuk (1990), Topp et al (1997), Bergamin et al (2010), and Conte et al (2011).The soil used in recomposition of the mined area can reach its final construction stage in varying degrees of disintegration and compaction (Akala and Lal, 2001), and the use of machines at soil moisture close to the plastic limit is the main factor that causes compaction, since water reduces cohesion and acts as a lubricant between soil particles, allowing sliding and packing of particles when the soil is subjected to some sort of pressure (Luciano et al, 2012).…”

“…A vital component in exploitation of mineral resources is recovery of areas that have been degraded by the mining process, especially in the case of surface mining, which has major impacts on soil and landscape (Yada et al, 2015) due to the removal of vegetation cover and layers of soil and underlying rocks (Mukhopadhyay et al, 2013), resulting in total change of the soil profile (Stumpf et al, 2014).…”

“…A constructed minesoil is usually compacted by excessive machine traffic, which results in inadequate physical conditions for plant growth and development (Lunardi Neto et al, 2008;Sheoran et al, 2010;Borůvka et al, 2012;Stumpf et al, 2014;Sena et al, 2015), as well as a decrease in the biodiversity of soil fauna (Oliveira Filho et al, 2014) and carbon losses due to mechanical mixing of soil horizons (A, B, and/or C) during the operations of removal, transport, and placement of the soil (Ussiri and Lal, 2005;Leal et al, 2015). In addition to these impacts, in mine waste piles derived from coal processing (usually enriched in pyrite), the process of soil aggregation and structuring by the root system of cover crops can promote input of oxygen and water and increase the development of acid mine drainage in the reclaimed area (Quiñones et al, 2008;Campaner and Luiz-Silva, 2009;Costa and Zocche, 2009;Inda et al, 2010;Daniels and Zipper, 2010;Moura, 2014) Reclamation of a mined area should return a degraded ecosystem to a non-degraded condition, which may be different from the original environment (Ibama, 2011).…”

Initial Recovery of Organic Matter of a Grass-Covered Constructed Soil after Coal Mining

“…Although the covered constructed soil has a higher percentage of microaggregates (Stumpf et al, 2014b) and higher clay content compared to natural soil (Table 1), the MAC stock of covered constructed soil represented, on average, only 39 % of that of natural soil. This can be attributed to the constant addition of plant residues to the natural soil over the years and its low disturbance, leading to preservation of non-occluded OM associated with silt and clay fractions and to greater stability and protection of OM occluded in microaggregates (Six et al, 1998 (Table 3) reinforces this interpretation.…”

“…The data of the chemical properties of the constructed soil can be found in the study of Stumpf et al (2014b). ) with a total relative neutralizing power of 100 % and a fertilizer mixture (900 kg ha -1 N-P-K, 5-20-20) were applied.…”