Weed seedbank communities of organic farms: A comparison of New England, the Midwestern United States, California, and the Netherlands
Weed communities on organic farms vary widely in density and diversity from their conventionally managed counterparts, but only a handful of studies report weed seedbank data from organic farms. We will present a detailed comparison of weed seedbanks on 91 organic farms from four distinct regions: northern New England, the Midwestern United States, California, and the Netherlands. Soil samples were collected to a depth of 10 cm from 3-5 fields at each farm in 2010 or 2011, and then germinated, identified, and counted in the greenhouse. Germinable weed seedbank density, diversity measures including richness and evenness, and community composition were measured.
Seedbank density significantly differed between regions with highest mean weed seed density in the Midwest (12,215 seeds per m-sq), followed by New England (8,739 seeds per m-sq), the Netherlands (4,453 seeds per m-sq), and California (1,693 seeds per m-sq). Notably, each region included high seedbank density farms with densities greater than 20,000 seeds per m-sq. The lowest seedbank density farms in each region varied from 13 seeds per m-sq in California to 2,774 seeds per m-sq in New England. Weed species community composition revealed shared and unique weeds of concern in each region. There were associations between community composition and farmer perceptions of their most problematic weeds. For example, on New England farms, hairy galinsoga Galinsoga ciliata and crabgrass Digitaria spp. were most often reported as the most problematic weeds. These two species were also the most abundant in New England seedbanks. We will highlight distinctive management strategies and philosophies in each region, and the implications for education and outreach.