Effect of Land Use and Management on Soil Intra-Aggregate Properties Determined from µct Images.

Most techniques for soil analyses are destructive.  The advent of computed microtomography (µCT) has allowed for in situ, non-destructive analysis of soil aggregates that visualizes intact aggregates and their internal features.  Images obtained from µCT are 3D gray scale images in which the gray scale values (GVs) correlate to structural components of the studied material.  For soil samples, the important structural components influencing the GVs patterns are:  differences in mineralogy, distribution of solid/void space, and presence/amount of soil organic matter (SOM).  Because SOM has a lower density than the mineral phase, it typically has lower GVs (appears darker) on the images.  Our preliminary results indicated that intra-aggregate soil carbon is significantly correlated with image GVs.  Here we build on this relationship to explore spatial patterns in the GVs of intra-aggregate solid material in relation to positions and characteristics of soil pores. We assume that the GV patterns will serve as an indirect indicator of SOM patterns.  The study examines the GV distributions around intra-aggregate pores from aggregates originated under three different long term management practices:  conventionally managed corn-soybean-wheat rotation system, organic corn-soybean-wheat rotation system with cover crops, and native succession vegetation.  Layers selected at 13-78 μm, 78-143 μm and 143-205 μm distances away from defined pores were explored using GVs, normalized to the average GVs of the solid material of the entire image.  Results show that GVs tend to be darker and more variable near the pores and lighten farther away from the pores for aggregates from all three studied management systems.    One of the possible causes for the observed pattern is SOM accumulation near the pores with little SOM movement farther from the pores. Results of these and additional analyses will be presented and discussed.