Intra‐aggregate Pore Characteristics: X‐ray Computed Microtomography Analysis

Abstract

Intra-aggregate pores play an important role in controlling soil processes on a micro-scale. Differences in parent materials, pedogenic processes, land use, and management practices can have a substantial effect on their characteristics. The goal of this study is to examine intra-aggregate pore characteristics using X-ray computed microtomography (μCT) images in soils of two contrasting parent materials and of contrasting land use and management. In addition, to quantify pore characteristics in aggregate exterior and interior layers we have developed an approach for aggregate boundary delineation in μCT images. Soil aggregates from a Hapludalf under Long Term Ecological Research conventional tillage treatment (LTER-CT) and native succession vegetation treatment (LTER-NS) in southwest Michigan, and from an Ustochrept under native succession vegetation and bare soil in northeast China were used. The LTER-CT aggregates had significantly greater macro- porosity (>14.6 μm in diameter) than those of LTER-NS. The LTER-NS aggregates had more large pores (>97.5 μm) and more small pores (<15 μm) than LTER-CT aggregates, while more medium size pores (37.5–97.5μm) were found in LTER-CT aggregates. Greater abundance of medium sized pores in LTER-CT aggregates could be the cause of their reported lower stability and higher macro-aggregate turnover rate. The differences in pore size distributions between LTER-CT and LTER-NS were more pronounced in the aggregate interiors, as compared to the exterior layers. In aggregates from both studied soils large pores tended to prevail in the aggregate interiors while medium size pores (37.5–97.5 μm) were more abundant in the aggregate exteriors.