Soil Carbon and Nitrogen Stabilization Within Soil Aggregates Associated With Earthworm Middens In Boreal Climate Conditions.

Earthworm interaction with soil processes, including aggregation, decomposition of residues and aeration, has made earthworms a topic of interest when developing sustainable agroecosystems. Earthworms increase the mineralization of N and enhance the incorporation of soil organic carbon (SOC) from residues to casts therefore possibly improving the stabilization of soil C. It is suggested that the passage of soil through the earthworm gut enhances the formation rate of microaggregates (53–250 µm) within macroaggregates (>250 µm). These microaggregates offer a more stable long-term storage for sequestered SOC and N. Our objective was to determine if earthworm activity increased soil aggregation, the total SOC and N, and if the areas with higher earthworm activity had more SOC and N stored in the microaggregates within macroaggregates compared to areas with less earthworm activity. Soil samples to determine the distribution of SOC and N in different soil fractions were taken from anecic soil surface feeding Lumbricus terrestris L. midden and adjacent non-midden areas at three study sites under long-term no-till and analyzed by wet sieving and by further isolating microaggregates from large (>2000 µm) and small (250–2000 µm) macroaggregates.  Increased earthworm activity resulted in more large macroaggregates at the clayey sites (site 1 and 2) but less smaller macroaggregates at site 2. We found more SOC in the large macroaggregates in midden versus non-midden areas and in microaggregates within these large macroaggregates but there was no change in the level of SOC in microaggregates within small macroaggregates. A significant increase was found in the amount of total SOC between earthworm middens and surrounding soil. No changes, however, we found at the third site with coarse soil. These results suggest earthworms have a potential to increase soil aggregation and enhance the storage of SOC and N to more protected, stable microaggregates in clayey no-tilled soils under boreal climate conditions.