Winter cereal rye (Secale cereale) (WCR) is often double cropped with corn for silage (Zea mays L.) to increase farm forage supply and profit. Winter cereal rye might respond to nitrogen (N) at different harvesting times. Therefore, two on-farm trials were conducted in the 2019-2020 and 2020-2021 growing seasons to evaluate the effect of harvesting time (late-March to end-of-April considering the growth stage) and spring N fertilization (0 vs. 47 kg N ha-1) on WCR morphology, forage yield, nutrient removal, and quality. A quadratic model best explained an increase in WCR biomass in response to growing degree days (GDD) accumulation (R2 = 0.81). An increase in GDD linearly decreased WCR relative forage quality (RFQ). Benchmarking RFQ at 150 for dairy milk production indicates WCR should be harvested at a GDD of 543, at which WCR plant height was 31.8 cm and dry matter (DM) biomass was 0.77 Mg ha-1. Benchmarking RFQ at 125 for heifer production indicated that harvest should occur at a GDD of 668, at which the WCR was 71 cm tall, and its DM yield was 2.25 Mg ha-1. Nitrogen balances were negative at the zero-N control treatment (0 kg N ha-1), indicating a need for some N to maximize WCR yield. We found that a rate between 21 and 42 kg N ha-1 maximizes yields reflecting slightly positive balances. Our results suggest that the harvesting time can be predicted by GDD and should be adjusted for RFQ. We conclude that less than 42 kg N ha-1 N fertilizer is required for WCR production in soils with manure history and high soil organic matter (>30 g kg-1).
