Nitrogen Use Efficiency and Yield Response of High Biomass Sorghum in the Lower Midwest

Core Ideas Two‐year study evaluating high biomass sorghum yield response to a broad range of N treatments. A minimal N fertilizer rate of 56 kg ha−1 is needed to increase average ethanol yield to 5519 L ha−1, with no additional yield benefit at greater N rates. Yields were limited by varying environmental conditions and delayed planting. Nitrogen recovery efficiency were greatest at low N rates, but N use efficiency more stable across N rates, but greatly impacted by environment. High biomass sorghum [Sorghum bicolor (L.) Moench] could potentially produce high yields in the midwestern United States with minimal fertilizer inputs. However, little is known about the yield response, N uptake, nitrogen use efficiency (NUE), and nitrogen recovery efficiency (NRE) of high biomass sorghum (HBS) at varying N fertilization rates when grown for lignocellulosic ethanol. The objectives of this 2‐yr study were to determine the effect of five N rates (0, 56, 112, 168, 224 kg N ha−1) on the dry matter (DM) yield and lignocellulosic ethanol yield (LEY), and the NRE and NUE of two HBS varieties in the midwestern United States. The two varieties responded similarly for most measured parameters. Total DM yield averaged 13.1 Mg ha−1 and estimated LEY averaged 5519 L ha−1 across N rates when grown in central Missouri. Nitrogen rates between 56 and 224 kg N ha−1 resulted in similar DM yield and LEY in 2010, and there were no yield differences among N rates ranging from 0 to 224 kg N ha−1 in 2011. The greatest N removal in DM was at or above 56 kg N ha−1. Nitrogen recovery efficiency and NUE differed by year, where low rainfall and a shortened growing season in the second year resulted in reduced NRE and NUE. Lack of NUE and DM yield differences at N rates above 56 kg N ha−1 indicates the potential for producing high biomass sorghum with minimal amounts of fertilizer N in the Midwest.