Aggregate formation pathways as indicators of soil health in different grazing systems in the Brazilian Pampa

Soil health is the soil’s ability to perform physical, chemical, and biological functions, promoting ecosystem services intrinsic to its edaphoclimatic specificities. In this context, identifying the origin of aggregate formation pathways can act as an indicator of soil health, as it directly reflects management practices that influence physical structure and biological activity. Different aggregate formation pathways indicate distinct forms and amounts of carbon, which require further investigation; however, the first step consists of morphologically separating physical and biological aggregates. The objective of this study was to quantify, through visual assessment, biogenic and physicogenic aggregates. Soil samples were collected at depths of 0–10, 10–20, and 20–30 cm in improved native pasture and unimproved native pasture areas located in Eldorado do Sul, RS, on a sandy clay loam Ultisol. Aggregate classification was based on visual identification, using a microscope, of biological structures (such as macropores and roots) and aggregate shape, considered angular (physicogenic) or rounded (biogenic). Preliminary results in the unimproved pasture indicate a predominance of physicogenic aggregates: 70% in the 0–10 cm layer and 80% in the 10–30 cm layer. In the improved areas, biogenic aggregates represent 55% and 40%, respectively. These results indicate a shift in the dominant aggregate formation pathway in response to management practices; however, gaps remain in identifying the amount of carbon associated with each formation pathway, which will be addressed during the development of this study.