Effect of agricultural management on soil aggregates as determined from computed microtomography images

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Different agricultural managements are known to affect soil properties differently.  Soil aggregation, soil organic matter content, compaction and nitrogen mineralization are just a few factors known to depend on agricultural management at the field scale.  However, the effects of agricultural management on the aggregate scale are much less understood, even though many important processes take place at the aggregate scale (microbial processes, soil organic matter protection, etc.).  Using computed microtomography, 3D gray scale images of soil aggregates at micron scale can be obtained  The gray scale values correlate to mineralogical differences, as well as, pore/void space and organic matter.   Mineral material appears lighter while pores/organic matter appears darker on gray scale images .  In this study, aggregates from three agricultural managements (T1, T4 and T6) from Kellogg Biological Station Long Term Ecological Research Main Site were investigated to determine the effect of management on the soil within aggregates at 13-78 um, 78-143 um and 143-205 um from image identified pores (>13 um).  For all treatments, the soil is darker at 13-78 um and lightens at 78-143 um and 143-205 um.  The soil variability is highest at 13-78 um and decreases at 78-143 um and 143-205 um.  This might indicate that soil organic matter is concentrated near the pores and decreases away from the pores.  T4 and T7 are significantly (a=0.05) lighter and more variable than T1 at 143-205 um only.  This difference might be due to roots compacting the soil as they push through.  Root derived pores occur more frequently in T4 and T7 than T1.