Concern over the consequences of increased weed seed inputs to the soil seed bank during the transition period from conventional to organic production is one obstacle to grower adoption of reduced input and nonchemical weed management strategies. An 11-yr study was established in southwest Montana to investigate the effect of a single pulse of wild oat seeds on subsequent seed bank dynamics. In 1993, wild oat seeds were sown at five densities (0, 20, 80, 320, and 800 seeds m⁻²) in eight wheat–small grain cropping systems that differed in the number of crops in rotation and fallow periods. Wild oat seed banks were measured each spring from 1994 to 2004 in half of the cropping systems and from 2001 to 2004 in all eight systems. In 1994, seed bank densities in response to the pulse were as much as 11 times higher than controls that received no seeds in 1993. By 1996, after mechanical fallowing of all cropping systems, wild oat seed bank densities were not significantly different from densities in control plots regardless of the size of the initial seed pulse and remained so through 2004. These data suggest that increases in wild oat seed inputs during the organic transition period will have relatively few long-term agronomic effects on the dynamics of wild oat seed banks in these systems. In addition, wild oat seed banks may be constrained by factors other than cropping sequence when herbicides are not used, such as possible density-dependent regulation as a result of increased soil pathogen attack and seed predation.

Nomenclature: Wild oat, Avena fatua L. AVEFA, wheat, Triticum aestivum L