Long-Term Stover Removal Decreases Soil Aggregate Stability in a Dryland Continuous Corn System.

Corn stover has been identified as a primary biofuel feedstock for supporting cellulosic ethanol production.  The long-term impacts of corn stover removal on soil physical quality and erosion potential will affect the sustainability of harvesting crop residues.  Surface soils (0-5 cm, 5-10 cm, and 10-30 cm) were evaluated for soil aggregate distribution and wet aggregate stability following 12 consecutive years of corn stover removal (50% removal rate) at a dryland no-tillage continuous corn site in the western Corn Belt.  Long-term corn stover removal generally decreased the size of soil aggregates (mean weight diameter) in 0-10 cm soils.  For all soil depths, however, the proportion of large soil aggregates (> 2 mm diameter) decreased and smaller aggregate size classes (0.053-2 mm diameter) increased in soils where stover was removed compared to those where stover was retained.  Aggregate size distributions were not affected by nitrogen fertilizer rates (60, 120, 180 kg N ha-1) or by N-by-residue removal interactions.  The wet aggregate stability of 0-5 cm soils tended to be lower when residue was removed, though the effect was not significant.  The breakdown of larger aggregates with stover removal was correlated with significant losses in particulate soil organic matter (POM) in 0-10 cm soils, despite measured increases in total soil organic carbon (SOC) in this depth increment since the beginning of the study (1998).  Significant increases in the 0.053-2 mm aggregate size classes and decreases in POM suggest that soils in this dryland continuous corn system are at increased risks for erosion and loss of soil carbon as POM, respectively, despite the use of no-tillage practices.