Agronomic management during the 3-yr transition period to organic certification influences soil quality and the weed seedbank. We studied two cropping systems during the transition period and the first certified organic season. A 4-yr rotation of corn, soybean, wheat/alfalfa, corn (C-S-W/A-C) [Zea mays L., Glycine max (L.) Merr., Triticum aestivum L., Medicago sativa L.], produced under a more complex management that included manure and cover crop residue, was compared to a perennial based corn, alfalfa, alfalfa, corn (C-A-A-C) rotation. We compared soil aggregate size distribution and bulk density after Year 1 and on completion of the transition period. Weed seedbank populations were quantified through two seasons in the greenhouse. Weed surface density and aboveground weed biomass were quantified in the field. Over the course of the study, the percentage of large soil macroaggregates (> 2000 mu m size class) had 2.7 and 3.4-fold increase for the C-A-A-C and C-S-W/A-C treatments, respectively. The C-S-W/A-C system generated a 4.5-fold increase in aggregates of this class when wheat that was interseeded with alfalfa was harvested as forage. Bulk density decreased 14 and 6% for the C-S-W/A-C and the C-A-A-C systems, respectively. There was a 60 to nearly 300% increase in total weed seeds germinated in the greenhouse for the C-S-W/A-C system. This same system had a 60 to more than 500% decreased weed seedbank density in the field. We conclude from this study that either strategy can improve soil quality while the weed seedbank was better managed in the more complicated C-S-W/A-C system.
