Broadcast interseeding cover crops into corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) instead of drill-planting after harvest extends the cover crop season and improves productivity, but establishment can be insufficient. Our objectives were to find broadcast seeding rates that result in maximum spring biomass and N uptake. We tested cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) in south-central and eastern Nebraska in 2016–2017 and 2017–2018. Seeding rates for rye were 341, 512, and 682 seeds∙m−2, and 119, 178, and 238 seeds∙m−2 for vetch. We broadcast in late September and terminated by early May. Fall emergence was between 3 and 54% of broadcast seeds, and greater for vetch. When broadcast into corn, rye spring biomass was 1472 kg∙ha−1 with N uptake of 38 kg∙ha−1. Vetch biomass was 361 kg∙ha−1 with 13 kg∙ha−1 N uptake. In soybean, rye produced 2318 kg∙ha−1 with 59 kg N∙ha−1 and vetch produced 535 kg∙ha−1 with 21 kg N∙ha−1. Higher seeding rates increased biomass and N uptake only for rye broadcast into corn. Year and site effects and possibly differences in main crops influenced cover crop productivity