Increased nitrogen fertilization of sweet sorghum drives increased uptake and removal of nine mineral nutrients in extracted juice and bagasse

Sweet sorghum [Sorghum bicolor (L.) Moench] has been reported to produce great yields of biomass and sugar for conversion to ethanol at relatively low N fertilizer levels but high N-use efficiency (NUE) when grown in the Midwestern U.S. Little previous research investigates the relationship of N management to the uptake and removal of many of the other important macro- and micronutrients in sweet sorghum. This can influence ethanol conversion efficiency and the long-term agronomic sustainability of sweet sorghum production. This two-year study examined the effects of five N fertilization treatments (0, 56, 112, 168, 224 kg N ha- 1) on the concentrations and contents of nine nutrients (P, K, S, Ca, Mg, Fe, Mn, Zn, and Cu) in extracted stem juice and bagasse of two sweet sorghum varieties (c.v. Dale and c.v. Top 76-6). Varietal and environmental (year) responses to N fertilization were few. In general, juice and bagasse nutrient concentrations stayed the same (Ca, Mg, Fe, Mn, Cu) or decreased (P, K, S, Zn) with increasing N rate at or above 112 kg N ha- 1, with a few exceptions. The applied N did not influence uptake and removal of P, K, and Zn in stem juice and bagasse, but Ca, Mg, S, Fe, Mn, and Cu contents increased with increasing N application. Most concentrations of different nutrients, including N, were positively correlated in both juice and bagasse. Results indicate that N fertilization increases the removal of many of the plant essential nutrients and that producers could alter N management of sweet sorghum for ethanol conversion to manipulate the mineral profile as well as target sustainable nutrient management.