Optimizing Sweet Sorghum Production for Biofuel in the Southeastern USA Through Nitrogen Fertilization and Top Removal
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Sustainable bioenergy cropping systems require not only high yields but also efficient use of inputs. Management practices optimizing production of sweet sorghum [Sorghum bicolor (L.) Moench] for bioenergy use are needed. The effects of N rate (45, 90, 135, and 180 kg N ha−1) and top removal (at boot stage, anthesis, and none) on biomass, brix, estimated sugar yield, and N and P recovery of sweet sorghum cv. M-81E were investigated in Florida at two sites differing in soil type. Across all data, dry biomass yields averaged 17.7 Mg ha−1 and were not affected by N fertilization rate at either site (P > 0.10). Mean brix values ranged from 131 to 151 mg g−1 and were negatively related to N rate. Top removal, either at boot stage or anthesis, resulted in greater brix values and 13% greater sugar yields at both locations. Whole plant N recovery was positively and linearly related to N rate and ranged from 78 to 166 kg N ha−1, approximately two thirds of which was in leaf and grain tissues. Based on yield and nutrient recovery responses, optimal nutrient requirements were 90 to 110 kg N ha−1 and 15 to 20 kg P ha−1. Higher N fertilization led to greater N recovery, but little to modest gain in sugar yield. Thus, proper nutrient and harvest management will be needed to optimize sugar yields of sweet sorghum for production of biofuels and bio-based products. Further research is needed to refine management practices of sweet sorghum for bioenergy production, especially with regard to the use of leaf and grain tissues.
KeywordsSweet sorghum N recovery Sweet sorghum P recovery Sweet sorghum biomass partitioning Sweet sorghum nutrient partitioning Bioenergy Sweet sorghum ethanol
Financial support for this study was provided by a USDA Special Grant, the Florida Agricultural Experiment Station, a Florida Farm to Fuel Grant, and the Florida Energy Systems Consortium. We are grateful to Andrew Schreffler, Jim Boyer, Jeffrey Fedenko, Johnathan Holland, Randi Randell, Maninderpal Singh, and Arkorn Soikaew for laboratory and field support.
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