How Much N Should You Apply to Winter Cereal Double Crops in the Spring? an Evaluation of Agronomic, Economic, and Environmental Consequences.

Cereal rye (Secale cereal L.) and triticale (x Triticosecale Wittm.) grown as double crops in corn (Zea mays L.) silage rotations can increase on-farm forage production when supplied with sufficient nitrogen (N). Here we report yield and most economic rate of N (MERN) at green-up in the spring across 58 on-farm N-rate trials (21 cereal rye and 37 triticale trials, four replications, three years). Nitrogen was applied at dormancy break (0, 34, 67, 101, and 134 kg N ha^-1). Harvest was done at flag leaf stage in May. Regression tree analysis was performed to identify soil indicators that can predict yields and MERNs. Yield at the MERN ranged from 1.6 to 5.4 Mg DM ha^-1 for cereal rye (average of 3.6 Mg DM ha^-1) and from 1.5 to 6.8 Mg DM ha^-1 (average of 4.5 Mg DM ha^-1) for triticale. The MERN averaged 65 kg N ha^-1 for cereal rye and 59 kg N ha^-1 for triticale. However, 5 of the cereal rye sites (24%) and 15 of the triticale sites (38%) were unresponsive to N addition, while for 10 cereal rye sites (48%) and 13 triticale sites (35%) MERNs ranged from 78 – 100 kg N ha^-1. The MERN was primarily impacted by soil test P (STP), reflecting past fertility management. Highest MERNs (averaging 116 kg N ha^-1) were determined for sites with STPs between 5 and 13 mg kg^-1, buffer pH of 6.2 or less and soil nitrate levels below 3 mg kg^-1. We recommend 78 – 100 kg N ha^-1 for those sites. Soils lower in STP required less N while sites classified as high in soil test P (13 mg kg^-1 or higher Morgan STP), with less than 291 mg kg^-1 available Mg, and a buffer pH of 5.1 or less were unlikely to respond to N at green-up.