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• Macroaggregation was greater under NT compared to CT. • NT promotes occluded-C accumulation mainly in macroaggregates. • The increase in occluded-C accumulation leads to organomineral association. • Legume cover cropping favors the mineral-associated C enrichment in microaggregates. Both no-tillage and legume cover crops have been shown to increase soil organic carbon (SOC) in subtropical soils. However, the mechanisms underpinning management system effects on SOC accumulation are still not well understood. We used a combination of aggregate size and density fractionation to elucidate these mechanisms at a 30-year old experiment on an Acrisol in southern Brazil. The effects of two tillage systems [conventional system (CT) and no-tillage (NT)] combined with three cropping systems [oat/maize (O/M), vetch/maize (V/M) and oat + vetch/maize + cowpea (OV/MC)] were evaluated in the top 20 cm soil layer. Overall, macroaggregation (>0.25 mm) was significantly influenced by tillage with NT showing values 14% greater than CT in the 0–5 cm soil depth. On average, the occluded light fraction-C content in macroaggregates was more than twice as high under NT compared to CT (4.4 vs. 1.8 g kg−1). This effect was more pronounced when legume cover crops were grown. However, the most significant effect of cover crops was observed in the organomineral fraction of microaggregates, especially under NT (12.1 under O/M and 19.8 g kg−1 under OV/MC). Our results suggest that, although NT increased the occluded light fraction-C compared to CT, this effect was smaller than the gains that legume cover crops offered in organomineral association. [ABSTRACT FROM AUTHOR]

Revegetation with different plant species has been a strategy to restore the minesoil profile quality in many countries. However, restoration studies about soils degraded by surface coal mining show that it is not easy a simple task to bring back degraded/mined soil to its near original configuration. Thus, our study monitored the physical restoration of a minesoil by 10.6 years over the same experimental unit used by Pauletto et al. (2016), when the minesoil was with 4.8 years of revegetation. The study was conducted in a coal mining area in Candiota city, Southern Brazil. The minesoil was constructed in early 2003, and the experiment was set up between September/October 2007. The species analyzed were Urochloa humidicola , Panicum maximum , and Urochloa brizantha. Natural soil under native vegetation was used as a reference. In April 2018, soil samples were collected in the 0.00–0.10 and 0.10–0.20 m layers, and the following soil attributes were determined: distribution of the water-stable aggregates in different size classes, tensile strength, soil organic carbon content, bulk density, total porosity, macroporosity, and microporosity. In addition, soil penetration resistance was measured in all experimental areas. The minesoil attributes improvement between 4.8 and 10.6 years occurred in depth, mainly with the cohesive aggregates breakdown, and macroporosity and soil organic carbon content increases. At 10.6 years of revegetation, all perennial grasses improved physical conditions up to 0.10 m depth of the minesoil, with good results than those observed in the natural soil. However, compaction persisted in the 0.10–0.20 m layer, as shown mainly by the higher tensile strength of the aggregates, soil penetration resistance, and bulk density. [Display omitted] • Minesoil compaction is a persistent problem even 10.6 years of revegetation. • Minesoil aggregates formed by compression due to traffic of heavy-machinery. • Tensile strength and penetration resistance evidence minesoil compaction. • Roots grasses promotes the breakdown of larger and cohesive aggregates. [ABSTRACT FROM AUTHOR]

Abstract: The Visual Evaluation of Soil Structure is a helpful tool for assessing the physical quality of soil, since it allows detailed examination of the soil structure as well as identification of layers modified by soil management. The Visual Evaluation of Soil Structure (VESS) method (Ball et al., 2007) has been applied in Brazil because it is simple and relatively objective, giving semi quantitative results quickly. It was used to determine the physical quality of soils under systems of no-tillage. In the present study, the potential for utilization of the VESS method was studied in three field experiments under no-tillage: (i) a comparison between mechanical and biological soil loosening, (ii) a study of changes in soybean yield and soil structural quality along a transect with a soil textural gradient, and (iii) a comparison with Visual Soil Assessment (VS) method (Shepherd, 2009) along the same transect. Overall the use of VESS proved to be an efficient semi quantitative methodology for assessing soil physical quality in Brazilian soils under no-tillage. [Copyright &y& Elsevier]

Abstract: In this study, the effects of soil bulk density, total porosity, organic matter content, aluminium saturation and cation exchange capacity (CEC) on water and ethanol sorptivity and hydro-repellency index of various sized aggregates of horizons A and B were investigated. Soil samples were taken from horizons A and B in 17 different locations of Rio Grande do Sul, Brazil. Three samples were collected from each of the horizons for the determination of soil sorptivity in water and ethanol. Soil sorptivity was determined by a steady-state flow using a mini-infiltrometer. Hydro-repellency of samples was estimated from the ethanol/water sorptivity values. Aggregates from most soil samples exhibited low hydro-repellency index, R (1.24–3.12), except for luvisol and vertisol, which had R ≥5.79. The very low coefficients of determination, r 2 =0.18 and 0.22 at p =0.01 between hydro-repellency index and organic matter content, and between angle of contact and organic matter content, respectively is an indication that the quantity of organic matter have little influence on hydro-repellency, but the composition of organic matter and other soil properties. The mean pH of sampled soils ranged from 3.90 and 5.50 in both horizons A and B but presents no significant effect on the hydro-repellency of soil at p =0.01. The results show that soil hydraulic and sorptivity properties are dependent on interaction between aggregate sizes, which is mainly a function of the soil clay minerals. [Copyright &y& Elsevier]