Nitrogen Management of Brachytic Dwarf Brown Midrib Forage Sorghum in New York

Abstract

Core Ideas Forage sorghum is a viable alternative to corn silage in the northeastern United States. Brachytic dwarf BMR sorghum can yield nearly 20 Mg DM ha–1 in the Northeast. Forage sorghum requires approximately 10 kg N per 1 Mg DM for optimum performance. Forage sorghum following manure or legume histories may not need additional N. ABSTRACTForage sorghum [Sorghum bicolor (L.) Moench] can be an alternative to corn silage (Zea mays L.) in the northeastern United States due to its drought tolerance and later planting date. Our objective was to determine the most economic rate of N (MERN) for a brachytic dwarf brown midrib (BMR) forage sorghum cultivar based on 13 N‐rate trials in New York from 2013 to 2017. Trials fell into one of three groups based on yield response to N: Group 1, no response (MERN = 0; n = 2); Group 2, no yield plateau (n = 4); and Group 3, yield plateau between the lowest and highest N rates (n = 7). Group 1 dry matter (DM) yields averaged 18.7 Mg DM ha−1 and included trials with manure or legume histories. Trials in Group 2 averaged 17.6 Mg DM ha−1 at the highest N rate with an increase of 38 kg DM per kg of N. Group 3 trial MERNs averaged 203 kg N ha−1 with a yield at the MERN of 19.9 Mg DM ha−1. Nitrogen use efficiency, apparent N recovery, and crude protein at the MERN of the Group 3 trials averaged 46 kg DM kg−1 N, 63%, and 80 g kg−1, respectively. Nitrogen did not greatly influence other nutritive value indicators. We conclude that the MERN of BMR forage sorghum is ∼10 kg N per 1 Mg DM yield. Additional trials are needed to confirm that fields with recent manure or legume histories may not require additional N.