Effects of Biosolids Application and Harvest Management On Switchgrass Biomass Production and Biofuel Feedstock Quality.

Reducing input costs by applying biosolids, optimizing N fertilization rates, and increasing yields on marginal land would improve the sustainability of biofuel systems. To this end, we determined the effects of biosolids application rate and harvest frequency on switchgrass yield, N concentration and removal. Switchgrass was harvested once (November) or twice (July and November) per season. Anaerobically digested, pasteurized and dewatered biosolids were applied once at 0, 153, 306, and 459 kg N ha^-1 in May 2010. Switchgrass yield, N concentration, and N removal were determined for three years. Biosolids increased switchgrass yield, N concentration, and N removal in biomass in all years.  Switchgrass yield was greater with the two-cut system (11.9 vs 9.8 Mg ha^-1) except in the first growing season (5.4 vs 3.4 Mg ha^-1), which was affected by a summer drought. In November, plant N concentrations were higher in biomass under two-cut management (9.9 vs. 6.4 g kg^-1). Cutting twice per season removed almost 50% more N than the one-cut system. Combining low biosolids application rates with two-cut management came closest to balancing N inputs and outputs. Differences in N removal between harvest systems largely reflected differences in N concentration rather than differences in yield. Nitrogen use efficiency, apparent recovery, and partial factor productivity were reduced as biosolids rates increased. Cutting twice per season can increase switchgrass yields and N removal, but may lower feedstock quality. Managing for balanced N inputs and exports may have a negative effect on biomass production with biosolids application.