Elephantgrass Exhibits Higher Biomass Production and Water Use Efficiency and Less Nitrate Leaching Than Bahiagrass.

Land-use conversion is necessary to grow crops for energy purposes. Florida has >2 million hectares of bahiagrass (Paspalum notatum Flugge) pastures, and part of these pastures could be replaced with bioenergy crops. Elephantgrass (Pennisetum purpureum L. Schum.; EG) has high biomass productivity (~40 Mg ha-1) and is adapted to southeastern US conditions. However, little is known about the ecosystem services EG provides and the sustainability of applying residuals of the bioenergy industry as alternative nutrient sources to grow EG. Lignocellulosic based ethanol production and thermal processing of biomass produce fermentation residual and biochar residual, respectively, which are nutrient rich materials that could be returned to the field to minimize soil fertility depletion and disposal issues of these bioenergy residuals to the environment. A 3-year field study was conducted to compare evapotranspiration, drainage, soil moisture reserve, water use efficiency (WUE), and nitrate loss between EG and bahiagrass. Additionally, we evaluated the use of fermentation residuals and biochar as soil amendments on EG growth and ecosystem services. Treatments consisted of i) bahiagrass + 50 kg N ha-1, ii) EG +50 kg N ha-1, iii) EG +50 kg N ha-1+ fermentation residual, iv) EG +50 kg N ha-1,+ biochar, and v) EG +250 kg N ha-1. EG produced 88% more dry matter and exhibited 87% higher WUE compared to bahiagrass throughout the study. Regardless of residual application, nitrate concentration in drainage was 77% lower in EG plots compared to bahiagrass. Land application of bioenergy residuals can reduce inorganic N fertilization requirements, maintain adequate EG biomass yield and reduce detrimental environmental effects associated with nitrate loss to groundwater.