Cover Crop Diversity and Management for Weed Control in Organic Agro-Ecosystems.

Weeds are a primary concern in agricultural production. Organic agriculture in particular requires advanced weed management tactics, as the use of synthetic chemicals is prohibited. Effectively choosing and managing cover crops can provide weed control and facilitate crop production via improvements in soil quality. Here we describe results from two experiments using cover crops in organic vegetable production. In a cover crop diversity experiment, we grew crookneck squash following winter cover crops of barley, crimson clover, a barley-crimson clover mix, or a no-cover crop control. In a tillage experiment, we grew sweet corn following a winter cover crop mix of rye, crimson clover, and forage radish. Cover crops were then managed in one of four tillage treatments: no-till, strip till, conventional till, and conventional till followed by black plastic mulch. In both experiments, we measured in-field weed abundance and diversity, and weed seedbank abundance and diversity. Considering the results of the two experiments, we found substantial reduction in weed abundance with the presence of cover crop surface residue, but minimal differences in weed suppression by cover crop type.  Only high-disturbance cover crop management (conventional tillage and black plastic) reduced the weed seedbank. Inclusion of a nitrogen–fixing legume (crimson clover) improved crop plant performance and yield. In one year of the cover crop experiment, sub-optimal cover crop biomass and heavy weed presence interacted with the presence of cover crops to substantially reduce crop performance.