Intra-Aggregate Pore Network Stability Following Wetting-Drying Cycles in a Subtropical Oxisol Under Contrasting Managements

One type of pore fundamental to water dynamics is the intra-aggregate pore, which holds water vital for plant and root system development, mainly in finer-textured soils such as clays. The distribution of intra-aggregate pores also influences the redistribution of water. Thus, it is important to study the dynamics of the intra-aggregate pore network under processes such as wetting and drying cycles (WDC). Changes in these pore types can play essential roles in organic matter protection, water movement, microbial activity, and aggregate stability. To date, there are few studies analyzing the impact of WDC on intra-aggregate pore dynamics. This study aims to provide results in this regard, analyzing changes in the pore architecture of a subtropical Oxisol under no-tillage (NT), conventional tillage (CT), and forest (F) after WDC application. Three-dimensional X-Ray microtomography images of soil aggregate samples (2–4 mm) subjected to 0 and 12 WDC were analyzed. The results showed that WDC did not affect (p > 0.05) the imaged porosity, number of pores, fractal dimension, tortuosity, and pore connectivity for the different soil management types. To analyze the permeability and hydraulic conductivity of the soil pore system, the most voluminous pore (MVP) was examined. No differences were observed in the imaged porosity, fraction of aggregate occupied by the MVP, connectivity, tortuosity, hydraulic radius, permeability, and hydraulic conductivity between 0 and 12 WDC for the MVP. Comparing soil management types after 12 WDCs, for example, F samples became more porous than CT and NT samples. In contrast, the pore system of NT had a lower fractal dimension and was more tortuous than that of CT and F samples. Our results show that for highly weathered soils such as the Brazilian Oxisol studied, the intra-aggregate pore network proved resistant to changes with WDC, regardless of the type of management adopted.