Exploring multifunctionality of summer cover crops for organic vegetable farms in the Upper Midwest

Intensive vegetable crop rotations can have detrimental effects on soil health, draining soil of organic matter reserves and necessitating nitrogen (N) inputs. In addition, many vegetable crop rotations leave little time or space to integrate beneficial arthropod and pollinator habitat into crop rotations; the lack of habitat may cause declines in beneficial arthropods, which can lead to insufficient pollination services and increased pest pressure. Nine treatments, each containing one to seven species of cover crops, were evaluated for flowering, aboveground biomass production and N content, soil-N contribution after biomass incorporation, and beneficial arthropod visitation. A seven-species mix composed of oat (Avena sativa L.), field pea (Pisum sativum subsp. Arvense L.) and five clover species (Trifolium spp.) added the largest amount of biomass (8747 kg ha-1). Likewise, this mix contributed the most organic N (265.6 kg N ha-1), and increased soil-N after biomass incorporation (10.9 mg-N kg-1 of soil). Buckwheat (Fagopyrum esculentum Moench) and phacelia (Phacelia tanacetifolia Bendth.) monoculture produced most abundant floral resources. Beneficial arthropods observed included pollinators (native, honey and bumblebees), predators (syrphid flies and green lacewings) and parasitoids. Increased floral diversity was associated with abundance of flies in the Syrphidae family. Phacelia monoculture was most attractive for bees in the Apidae and Halictidae family, both of which may provide pollination services. These results highlight floral visitation patterns as an indicator for beneficial insect community support and conservation, especially in summer months, when greater insect reproduction occurs. Summer-planted cover crops are an underexplored rotation option for organic farming systems in the Upper Midwest, and may provide a wide range of ecosystem services including increases in available soil N and beneficial arthropod populations.