Impact of compaction and post-compaction vegetation management on aggregate properties, Weibull modulus, and interactions with intra-aggregate pore structure

As building blocks of soil structure, aggregates shape the physical environment for soil biota, control available surfaces for nutrients, and are key in regulating soil functions including carbon and nutrient cycling, water flow and storage, and soil-atmosphere gas exchange. Abiotic and biotic processes play essential roles in aggregate formation. Consequently, soil management has a strong impact on characteristics and properties of aggregates. In this study, we quantified the impact of compaction and post-compaction management with and without vegetation (permanent grass and bare soil, respectively) on soil aggregate density, tensile strength, fractal dimension, friability and on pore structure within aggregates. Based on theory from material science, we hypothesized that the Weibull modulus, which is a measure tensile strength variability, reveals information on the pore structure within aggregates. Our results show that compaction had a stronger effect on aggregate density and tensile strength than vegetation. Soil friability was highest in the permanent grass control treatment and lowest in the compacted bare soil. Quantification of intra-aggregate pore structure of these contrasting treatments revealed that aggregates from the permanent grass control treatment had a more complex pore structure and longer pores than aggregates from the compacted bare soil. As a result, we show that friability is driven by intra-aggregate pore length rather than aggregate density. Weibull modulus was strongly correlated with intra-aggregate pore structural features (pore-length distribution, number of pore branches and junctions per volume). However, the relationships between Weibull modulus and pore characteristics were treatment specific. The temporal evolution of Weibull modulus could be a helpful metric to better understand how different pore features recover from compaction over time.