Across the US Midwest agricultural region, cereal rye ( Secale cereale L.) and other cool-season grasses remain the most common cover crops ( Singer, 2008). Vegetable farmers often grow multiple cash crops during the growing season, leaving few periods of bare ground and thus limiting opportunities for cover crop use. This interest is particularly high among organic growers, who are mandated to follow practices that combine soil fertility and pest management with biological processes ( Bellows, 2005). Recent surveys indicate increased farmer interest in and adoption of cover crops, with the majority of respondents reporting that cover crops have improved soil health on their farms ( SARE CTIC, 2017). Cover crop effectiveness is typically measured by the degree of contribution to supporting or regulating services, or indirect effects of maintained cash crop yield ( Kaspar and Singer, 2011 Schipanski et al., 2014). Because cover crops increase rotational diversity, they may also provide important contributions to farming system resilience ( Bowles et al., 2020). Cover crop integration into vegetable rotations can perform supporting and regulating services such as contributing to soil carbon, nitrogen contribution, and pest suppression ( Ding et al., 2006 Bulan et al., 2015 Blesh, 2018). Intensive production practices characterizing typical vegetable farming focus on maximal cash crop yield (provisioning services) to the detriment of supporting or regulating ecosystem services ( Smuckler et al., 2012). Summer cover crops, because of their biomass accumulation potential, may be used by farmers in northern climates to fit into cropping system niches that have historically been left as bare soil, but care with timing is necessary to optimize weed suppression and mitigate tradeoffs for cash crop production. Broccoli in Y2 did not reach maturity due to fall freeze. Data from Y1 show that cover crops were unable to replace fertilizer for fall broccoli yield, and led to reduced fall crop yield. Most cover crops did not outcompete weeds, but treatments with less weeds produced more overall biomass. Mean total biomass (cover crop + weeds) by site year ranged from 1,890 kg ha −1 in MN Y1 to 5,793 kg ha −1 in WI Y2 and varied among species in Y1 for both the SD and LD treatments. To quantify effects on cash crops, we measured fall broccoli yield and biomass. To quantify cover crop quantity, quality, and weed suppression capacity, we measured cover crop and weed biomass, and biomass C:N. Our study included four site years, during which we investigated the effects of four cover crop species treatments, grown for 30 (short duration, SD) or 50 days (long duration, LD) alongside bare fertilized and unfertilized control treatments: buckwheat ( Fagopyrum esculentum) and sunn hemp ( Crotalaria juncea) monocultures, and biculture of chickling vetch ( Lathyrus sativus) or cowpea ( Vigna unguiculata) with sorghum-sudangrass (sudex) ( Sorghum bicolor x S. This project evaluated summer cover crops in the northern USA (MN and WI) for biomass accumulation, weed suppression, and contribution to fall cash crop yield. In northern climate vegetable systems, warm-season cover crops planted during short summer fallows could be a tool to build resilience via ecosystem service enhancement. Vegetable farming often includes spring and fall production, limiting establishment and productive potential of over-wintered cover crops that are more widely used in the USA. Diversification with cover crops may support increased resilience through soil organic matter (SOM) contributions and physical soil protection. Intensive production practices characterizing vegetable farming contribute to high productivity, but often at the expense of supporting and regulating ecosystem services.
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