Nitrogen fertility and harvest management of switchgrass for sustainable bioenergy feedstock production in Illinois

To meet the U.S. government goals for cellulosic biofuel production, more than 300 million metric tons of lignocellulosic feedstock must be collected annually by 2022. Perennial grasses, such as switchgrass (Panicum virgatum L.), are expected to play a vital role in meeting these biomass demands. Determining optimum nitrogen fertilization practices and harvest timing will be essential to maximize yields, ensure stand longevity, and optimize feedstock quality. A field experiment was conducted from 2009 to 2012 at six locations in Illinois to determine the effect that N source (urea and slow-release N), N application rate (0, 56, 112, 168, and 224 kg N ha⁻¹), and harvest timing (late summer, late fall, and early spring) have on above ground biomass yield and quality. The nitrogen source generally had no effect on biomass yield, moisture content or composition. Biomass yields increased with increasing N rates at each harvest timing with the highest yields occurring with 224, 168, and 112 kg N ha⁻¹ for summer (12.9 Mg ha⁻¹), fall (9.0 Mg ha⁻¹), and spring (6.7 Mg ha⁻¹) harvests, respectively. Moisture content was not affected by N rate and steadily decreased with delayed harvest timings. In general, cellulose, and hemicellulose contents were highest and lignin, protein and ash contents lowest when plots received 56 kg N ha⁻¹ at all harvest timings. Based on this study, we recommend applying N fertilizer at 56 to 112 kg N ha⁻¹ and harvesting from late fall to early spring to optimize switchgrass production in Illinois.