Aggregation as soil quality indicator in areas under different uses and managements

This study aimed to evaluate the influence of different land uses, with contrasting vegetation covers and planting systems, on the formation pathways of aggregates (biogenic and physicogenic) and on their chemical and physical attributes. The study was conducted in the municipality of Guaíra in the western region of the state of Paraná, Brazil. Five treatments were selected for the study: an area with a conventional tillage system (SPC), no-till system with 6 years (SP6) and 18 years (SP18) of implementation, permanent pasture (PP) with 45 years of planting, and reference area with native forest (NF). In each area, four soil blocks (undisturbed samples) were collected from the 0.00–0.05 and 0.05–0.10 ​m layers. Aggregates were classified according to their formation pathways as biogenic or physicogenic, and the chemical attributes, aggregate stability, particle size, density fractionation of soil organic matter (SOM), and natural abundance of carbon (13C) were characterized. In the CTS area, lower pH values were observed for both aggregate formation pathways, and biogenic aggregates had the lowest calcium (Ca2+) content. In the NTS18 area, there was an increase in SOM content for both formation pathways, and the quantified values were similar to those observed in the NF area, with increase in total organic carbon (TOC) content and in the labile and recalcitrant fractions of SOM when compared with those of CTS. Significant differences were observed between aggregates formed in the forest area and those formed in other systems, indicating that different pathways can be used as indicators of soil quality. The chemical and physical parameters evaluated in the biogenic and physicogenic aggregates allowed the separation of the study areas through principal component analysis, with an emphasis on NTS18, which was separated from the other areas, demonstrating that long-term conservation management increased the mineral organic matter and TOC levels.