Optimizing preplant nitrogen rate for early versus late biomass sorghum in the US Mid‐Atlantic

Abstract Biomass sorghum [ Sorghum bicolor (L.) Moench] is an alternative biofuel feedstock to maize [ Zea mays (L.)]. One advantage of biomass sorghum over maize is relatively lower nitrogen (N) requirement and its ability to tolerate late planting or fit into double cropping systems. To evaluate the most economic rate of N (MERN) for biomass sorghum in the Mid‐Atlantic region, a 3‐year (2017, 2018, and 2019) field trial was conducted at two locations (Holland and Hare) in Southeastern Virginia. Treatments were two planting dates (early [EP] versus late [LP]) and seven N rates (0, 56, 112, 168, 224, 280, and 336 kg ha −1 ) conducted in six environments. Data on dry matter yield of biomass sorghum, plant height, stem diameter, susceptibility to foliar diseases, and stalk lodging were recorded. Between the two planting dates, EP had 52%, 19%, and 16% higher dry matter, plant height, and stem diameter, respectively, compared to LP. However, LP exhibited lower disease pressure in four of 6 site‐years and lodging severity likely in response to weather conditions. Nitrogen rates between 112 and 224 kg ha −1 significantly improved dry matter, plant height, and stem diameter, with lower disease and lodging severity. At the MERN of 123 kg ha −1 , dry matter yield (20.66 Mg ha −1 ), plant height (454 cm), disease (61%), and lodging severity (34%) were least as compared to other treatments. Application of N at 123 kg ha −1 can provide the highest economic return while reducing the potential for N loss in the Mid‐Atlantic region.