Erosive strengths of concentric regions within soil macroaggregates

The stability of soil aggregate structures is very important for controlling aggregate dynamics and associated biogeochemical soil processes that respond to management and other physical disturbances. We examined the mechanical strengths of concentric soil layers from the surfaces to the centers of individual soil macroaggregates and compared them with polar tensile strengths (T-s), total soil C contents, soil texture, and bulk density of aggregates. Aggregates were sampled at depths of 0 to 5 cm from conventionally tilled (CT), no tilled (NT), and native forest (NF) ecosystems of a Wooster (fine-loamy, mesic Typic Fragindalf) and a Hoytville (fine, illitic, mesic Mollic Epiaqualf) soils Erosive strength (E-s) of aggregates was defined as the surrogate for erosive forces required to remove 1 g of soil during 1 min from the Surface of a soil aggregate rotating along the abrasive wall of a soil aggregate erosion (SAE) chamber. Total E-s values of macroaggregates were consistent with T-s of whole aggregates and were controlled by aggregate size and treatment. The E-s increased with decreasing aggregate size and from the exterior to the interior regions of aggregates. Measured changes in soil C content, texture, and bulk density across the different regions within aggregates did not completely explain the spatial distributions of E-s among concentric layers within macroaggregates. Higher contents of C and clay contributed to the greater strengths of the Hoytville soil aggregates, regardless of bulk density. On the other hand, E-s of soil aggregates from coarser-textured Wooster soils were correlated primarily with bulk density and appeared to be independent of C content.