Cover crops can serve as a valuable management tool for improving soil and water quality, but are an added expense for farmers. We evaluated the yields and economics of four cover crops and two winter fallow treatments in a spring wheat (Triticum aestivum L.)-soybean [Glycine max (L.) Merr.] rotation at three sites in Minnesota. The four cover crop treatments were winter rye (Secale cereal L.), forage radish (Raphanus sativus L.), winter camelina [Camelina sativa (L.) Crantz], and pennycress (Thlaspi arvense L.) planted into spring wheat stubble. The fallow treatments consisted of no-tilled and conventionally tilled soil. Radish winterkilled and rye was terminated chemically before planting soybean in early May. Soybean was inter-seeded between rows of camelina and pennycress at the same time it was planted in other treatments. Camelina and pennycress were harvested over soybean seedlings in late June. Camelina yields ranged from 600 to 1100 kg ha -1 , while pennycress ranged from 900 to 1550 kg ha -1 . Mono-cropped soybean averaged 1819, 3510, and 4180 kg ha -1 in northern, central, and southern Minnesota, respectively. Soybean seedlings under oilseed cover crop canopies exhibited lightstress, which likely reduced soybean yield in these treatments by 22 to 30%. When oilseed and inter-seeded soybean yields were combined, total seed yields generally were equal to or exceeded those of mono-cropped soybean. In addition, net income for inter-seeded systems was typically equivalent to mono-cropped soybean. Improvements in net income are likely needed before the benefits of oilseed cover crops are fully realized.• Net income from relay cropping was rarely different from that of mono-cropping. • A 25-cm oilseed row spacing was likely too narrow for optimal soybean growth. • Further domestication of oilseeds will likely improve relay cropping with soybean.

Winter cover crops might reduce nutrient loss to leaching in the Upper Midwest. New oilseed‐bearing cash cover crops, such as winter camelina (Camelina sativa L.) and pennycress (Thlaspi arvense L.), may provide needed incentives. However, the abilities of these crops to sequester labile soil nutrients are unknown. To address this unknown, N in shoot biomass, plant‐available N and P in soil, and NO3−–N and soluble reactive P in soil water collected from lysimeters placed at 30, 60, and 100 cm were measured in cover crop and fallow treatments established in spring wheat (Triticum aestivum L.) stubble and followed through a cover crop–soybean [Glycine max (L.) Merr.] rotation. Five no‐till cover treatments (forage radish [Raphanus sativus L.], winter rye [Secale cereale L.], field pennycress, and winter camelina) were compared with two fallow treatments (chisel till and no‐till). Pennycress and winter camelina were harvested at maturity after relay sowing of soybean. Winter rye and radish sequestered more N in autumn shoot biomass, ranging from 26 to 38 kg N ha−1, but overwintering oilseeds matched or exceeded N uptake in spring, ranging 28 to 49 kg N ha−1 before soybean planting. Nitrogen uptake was reflected by reductions in soil water NO3−–N during cover crop and intercropping phases for all cover treatments (mean = 4 mg L−1), compared with fallow treatments (mean = 31 mg L−1). Cash cover crops like pennycress and winter camelina provide both environmental and potential economic resources to growers. They are cash‐generating crops able to sequester labile soil nutrients, which protects and promotes soil health from autumn through early summer. Core Ideas Alternative, easily established winter‐surviving covers are needed in the Upper Midwest. Cover crops sequestered N and reduced soil and soil water NO3−–N in autumn compared with fallow. Winter oilseed crops reduced soil water NO3−–N in autumn through soybean planting. Novel winter oilseeds provide environmental and economic incentives to enhance adoption.