First validation of the method Visual Evaluation of Soil Structure in coal mining area using a long-term field revegetation experiment as testbed

Topsoil compaction is a persistent problem in minesoils, jeopardizing the revegetation and ecological reclamation of the mined land. Evaluation of soil structural quality (Sq) through quantitative methods is usually labor-intensive and/or costly, especially if a large area has to be examined. Therefore, reconciling cost-effective and accurate diagnose of minesoil Sq is crucial. The Visual Evaluation of Soil Structure (VESS) is a spade-based method scoring the soil Sq from 1 (good) to 5 (poor), which has not yet been validated for minesoils, and this was exactly the aim of this study. We made use of our long-term field experiment where quantitative physical attributes differed between perennial grasses used for minesoil revegetation, creating a Sq range to be screened by VESS. The minesoil, located in Southern Brazil, was revegetated for 14.3 years with Hemarthria altissima, Paspalum notatum, Cynodon dactylon, and Urochloa brizantha. The Sq of the minesoil (0.00–0.10 and 0.10–0.20 m layer) was evaluated by VESS and tensile strength of aggregates (TS), soil macroaggregates and microaggregates (%), soil organic matter (SOM) content, bulk density (BD), macroporosity (MaP), microporosity, total porosity (TP), and soil penetration resistance (PR). Through significant correlations between VESS scores and TS, MaP, macroaggregates (%), microaggregates (%), TP, SOM and especially BD (r = 0.60) and PR (r = 0.56), we found VESS to be a suitable method for reliable assessment of minesoil Sq. VESS scores 2.0–3.1 confirmed improved Sq at 0.00–0.10 m compared to 0.10–0.20 m (2.7–3.5), and this was supported by the ordination of 0.00–0.10 m samples together with SOM, macroaggregates (%), MaP and TP by principal component analysis. Moreover, VESS confirmed improved Sq in H. altissima (2.7) compared to C. dactylon (3.6) at 0.10–0.20 m, likely due to gains in soil MaP, TP, macroaggregates (%) and SOM. In this pioneering study we validated VESS as a practical and science-grounded method to monitor the Sq of a clayey subtropical minesoil.