Potential for Enhanced Nutrient Cycling through Coupling of Agricultural and Bioenergy Systems

Emerging markets for fuels and energy from crop biomass are creating new opportunities for redesigning agricultural systems for improved ecological function and energy‐use efficiency. Innovative bioconversion processes configured to recover key plant nutrients from biomass will allow recycling nutrients to crop fields, thereby closing nutrient cycles and reducing the energetic and economic costs of fertilization. Such advanced bioconversion matched with complementary biomass production may promote the development of highly productive agricultural–industrial systems that protect environmental quality. A generally representative example of nutrient recovery from an integrated biological and thermochemical conversion process designed to produce ethanol and synthetic fuels from switchgrass ( Panicum virgatum L.) indicates that approximately 111 kg ha −1 yr −1 of N can be recovered. This is equivalent to 78% of the N‐fertilizer input required. This example illustrates that N recovery and cycling could significantly improve the sustainability of biomass production as well as the overall energy balance of ethanol production from lignocellulosic biomass. Demand for lignocellulosic biomass as an industrial feedstock may also allow the introduction of new crops and cropping systems. In addition to perennial grasses, double‐crop sequences and systems incorporating greater use of legumes, cover crops, and living mulch may be able to produce large amounts of biomass while improving resource use efficiency and reducing environmental impact.