Print PageAn improved systems-level understanding of how different approaches to weed and soil quality management affect weed population and community dynamics is necessary to develop effective weed management practices in organic production systems. We assessed the density, composition and diversity of the readily germinable fraction of the soil weed seed bank in the spring and fall each year (2007-2010) following organic certification in four replicated feed and forage production systems in central PA. The four systems differed in the intensity of tillage during the three-year transition period prior to organic certification (full or minimum-tillage), weed population densities at the end of the transition period (low densities in full-tillage; high densities in minimum-tillage), and the subsequent approach to weed and soil management implemented during the three years following organic certification.
Results/Conclusions
Following organic certification, germinable weed seed bank densities increased more than four-fold by the final year of the study in system 1 (high initial weed densities due to minimum tillage during the transition period, and tilled only in the first of the three years following organic certification). In contrast, seed bank densities and species richness in the final year of the study were lowest in the system that employed the most intense tillage practices over the first two years post-certification (system 3), despite this system also having high initial weed densities due to minimum tillage during the transition period. Relative to the effect of the four management systems, the timing of seed bank sampling (spring versus fall) was a strong determinant of weed seed bank community composition. Smartweed (Polygonum spp.) and wild buckwheat (Polygonum convolvulus L.) were strongly associated with the spring seed bank, while purslane speedwell (Veronica peregrina L.) and field pennycress (Thlaspi arvense L.) were the most consistent indicators of the fall seed bank. Results from this study suggest that rotating minimum tillage practices (for soil quality improvement) with tillage-intensive practices (aimed at reducing weed populations) may be a viable approach to managing the readily germinable fraction of the weed seed bank. However, more work will be necessary to determine the optimal balance between full and minimum tillage phases over an organic rotation and how initial seed bank density and composition may dictate the periods of time within each phase (full or minimum tillage) required to realize desired goals for weed management and soil quality over the longer-term.
