Weed Seedbank Response to Cover Crops in Traffic Pathways Between Vegetable Production Beds Under Organic Management in the US Midwest

Abstract

Abstract Weed management is a primary barrier to sustainable organic vegetable production, and reducing the germinable soil weed seedbank is a critical long-term strategy for alleviating weed pressure. This study evaluated the effect of cover crops established in alleyways or traffic pathways on germinable warm-season weed seedbank density, species composition, functional group structure, and temporal emergence dynamics during transition to certified organic vegetable production. Treatments included three grass/legume cover crop bicultures of perennial ryegrass ( Lolium perenne L.)/white clover ( Trifolium repens L.), orchardgrass ( Dactylis glomerata L.)/red clover ( Trifolium pratense L.), sorghum-sudangrass [ Sorghum × drummondii (Steud.) Millsp. & Chas] /white sweet clover [ Melilotus officinalis (L.) Lam.], and a tilled fallow control. In the third year of the study, soil samples from cover-cropped and tilled fallow control pathways were subjected to a 60-day greenhouse emergence bioassay with observations recorded at 15, 30, 45, and 60 days after greenhouse setup. All three cover crop treatments reduced total germinable weed seedbank density by 73% to 82% relative to the tilled fallow, with no significant differences among cover crop treatments. Suppression was driven primarily by reductions in the annual broadleaf and annual grass functional groups, with carpetweed and foxtail identified as the principal species suppressed. Weed species richness did not differ among cover crop treatments or between cover crop treatments and the tilled fallow control. The tilled fallow produced a highly concentrated early emergence flush, with approximately 88% of total seedlings emerging within the first 15 days, whereas cover crop treatments substantially reduced and redistributed emergence across the monitoring period. Perennial ryegrass/white clover exhibited the most delayed peak emergence timing among all treatments. These findings demonstrate that traffic pathway cover cropping effectively suppresses the readily germinable warm-season weed seedbank during organic vegetable transition, with both annual and perennial cover crop bicultures providing equivalent suppressive benefits.