LAUSR

The potential benefits of different cover crops, biological control amendments, and vegetable rotation on soil chemical and biological properties, crop development and yield, and disease development in organic vegetable production, as represented by legume (green bean, Phaseolus vulgaris ), cucurbit (yellow summer squash, Cucurbita pepo ), and solanaceous (sweet pepper, Capsicum annuum ) vegetable crops, were evaluated in a multi-year field trial in Maine, USA. Cover crops evaluated included winter rye ( Secale cereale )/hairy vetch ( Vicia villosa ), mustard ( Brassica juncea ) green manure, a multi-species mixture (8 crops), and a fallow control. Overall, cover crops had only marginal effects on soil chemical properties, but all cover crops improved biological properties (microbial activity, populations, respiration) compared to fallow soil. The multi-species mixture and rye/vetch cover crops were associated with earlier emergence in beans and squash. All cover crops improved yield in beans and squash by 7–13%, but only the cover crop mixture increased yield for pepper (by 7–11%). Minimal crop diseases were observed throughout these studies, and biological control amendments, which included commercial formulations of Streptomyces , Trichoderma , and Bacillus sp., in general, did not positively affect yield, but reduced powdery mildew on squash and leaf necrosis on beans by 10–28%. The vegetable rotation also had significant effects, with beans yielding 8% higher following squash vs. pepper, squash yielding 15% higher following beans vs. pepper, and pepper yielding 11% higher following beans vs. squash. These results help define specific management practices to improve organic vegetable production and provide useful information and options for growers.