Agricultural management practices can cause changes in the weed seed bank, and understanding these effects can help producers better understand and manage weeds. Little work has been done to compare different organic management systems and their weed communities. The goal of this study was to assess what weed species were present in the soil weed seed bank, and growing aboveground, in the most recent crop rotation cycle (2017-2022) of the long-term Organic Cropping Systems (OCS) experiment. There are four different systems in OCS, all of which grow organic grain and forage, but differ in inputs and management practices. 1) the High fertility system receives high rates of nutrients, 2) Low Fertility receives low rates of nutrients, 3) Enhanced Weed Management has more frequent weed control events, and 4) the Reduced Tillage system focuses on soil health with less intensive soil disturbance.
We collected soil samples from the four treatments in 2017 and again in 2022, which were grown out in a greenhouse germination bioassay. We also sampled aboveground weed community biomass in each system in every year. We used weed abundance, taxonomic diversity, community-weighted means, and functional dispersion of weed traits in statistical models to assess the effects of the different treatments.
The Reduced Tillage system had the highest weed seed bank diversity (aka, the greatest number of species) and Enhanced Weed Management system had the lowest. Reduced Tillage and Low Fertility had higher functional dispersion of weed traits in the seed bank than did High Fertility. In High Fertility and Reduced Tillage, weeds were more likely to be short, have small seeds, and germinate early. The preceding crop had a large influence on these differences that were observed between systems. In aboveground weeds, crop species and rotation year influenced what species were found.
Results suggest that availability of nutrients and management events act as “filters” to influence what weed species survive in a given system.
