Micro- and Macro-Nutrient Composition of Sweet Sorghum Bagasse in Response to N Fertilization.

Sweet sorghum (Sorghum bicolor (L.) Moench) is a C4 annual grass that is capable of yielding high amounts of sugar, grain, and biomass under suboptimal environmental conditions.  Bagasse, the leftover biomass after stem juice extraction, can be used as a forage feedstock or combusted as fuel.  The mineral composition of bagasse can lower the energy outputs by favoring undesirable reactions and decreasing conversion efficiencies.  The objective of this study was to quantify the effects of N fertilization on the mineral composition of two sweet sorghum varieties (Dale and Top 76-6) from 2009-2011.  Mineral elements included in this study were P, K, Ca, Mg, S, Na, Fe, Mn, Zn, Cu, and B.  Overall, N fertilization did not drastically affect mineral composition except concentrations of Na and Mg.  This was especially apparent for 2011 when concentrations of Na and Mg were linearly related to N application rate.  In addition, concentrations of Na and Mg were greater in 2011 than in 2009 and 2010. These results may be accredited to drought stress in 2011 as the accumulation of Na and Mg have been demonstrated to occur in water-stressed plants.  Although there were no variety differences in total dry matter, Top 76-6 generally had greater mineral concentrations, including those that have negative effects in the energy conversion process (e.g. Na, Ca, Mg, S).  This study suggests that nitrogen fertilization and potentially water stress impact Na and Mg accumulation in sorghum bagasse which reduce potential energy outputs.