Can Biomass Yield of Switchgrass be Increased without Increasing Nitrogen Requirements?

Switchgrass ( Panicum virgatum L.) has been identified as a cellulosic bioenergy feedstock crop partly because of its potential to produce high biomass yields on marginal lands. Many breeding programs are focused on increasing biomass yields to improve the economic viability of the crop. However, increasing biomass yields without selecting for reduced biomass nitrogen (N) concentration will result in substantial increases in N removal at harvest. Our objectives were (i) to determine the current trajectory of biomass yield and N removal from breeding programs, (ii) to estimate the reduction in the rate of genetic gain for biomass yield when N concentration was incorporated into a breeding program, and (iii) to estimate the effects reduced N concentration might have on biofuel quality. Biomass yield and N concentration had a negative genetic correlation (−0.43), but a 50% increase in biomass yield likely will result in a 37% increase in N removal with direct selection for biomass yield. We estimated that incorporating the goal of reducing N concentration into a breeding program would result in a 225% greater reduction in N concentration while achieving 74% of the biomass yield gains achieved with direct selection for biomass yield only. Reducing N concentration in biomass was predicted to improve quality for use of biomass in a combustion system and to have minimal effects on quality in an ethanol conversion system. We conclude that simultaneous selection for increased biomass yield and reduced N concentration is both a worthy and feasible objective for switchgrass breeding programs that should improve the likelihood that improved yields from breeding are not undermined by increased N requirements.