Nitrogen Management of Brown Midrib Sorghum × Sudangrass in the Northeastern USA

Brown midrib (BMR) forage sorghum [ Sorghum bicolor (L.) Moench.] × sudangrass ( Sorghum sudanense Piper) hybrids (S × S) have been considered as a possible forage alternative to maize silage ( Zea mays L.) where maize planting is delayed due to wet soil conditions. Our objective was to determine the most economic rate of nitrogen (MERN) for BMR S × S grown in a two‐cut management system with a split application of N. Six field trials were conducted in New York in 2003 and 2004. One trial followed a grass–legume sod; a second trial had received liquid manure 19 mo before S × S planting. The remaining four followed S × S, silage maize, and/or a small grain crop. The MERN ranged from 137 to 192 kg N ha −1 cut −1 with dry matter (DM) yield ranging from 7.8 to 9.7 Mg ha −1 at the sites without additional N input. At the sites with prior N inputs, yield was higher (10.4–13.8 Mg ha −1 ) and MERN lower. The apparent nitrogen recovery (ANR) at the MERN was highest (61–73%) for the sites with prior N inputs. Nitrogen application rates > 145 kg N ha −1 cut −1 decreased nitrogen use efficiency (NUE) to <15 kg DM kg −1 N, while the ANR became <45%. We concluded that the MERN for BMR S × S grown in New York in a two‐cut system following maize, small grains, or forage S × S is 125 to 145 kg N ha −1 cut −1 . For sites that follow sod plow‐down or recent manure application, N application rates should not exceed 40 to 60 kg N ha −1 cut −1