Nitrogen Fertilization of C4 Grasses Grown for Bioenergy.

Nitrogen fertilization has the potential to significantly affect yield, nutrient concentration and removal and overall stand longevity of C₄ grasses grown for bioenergy production. While most studies report that these grasses need little to no fertilizer inputs to maximize yield, no specific recommendations have been given for fertilizer requirements across a wide range of C₄ perennial grass species, cultivars, harvest timings and N application rates.  Two field trials were established in the summer of 2008 in Ridgetown and Elora, Ontario to compare 4 miscanthus (M. sinensis and M. sacchiflorus crosses; Nagara and Amuri, and Miscanthus x giganteus; M1 Select and Polish), 2 switchgrass (Panicum virgatum L.; Cave-in-rock and Shelter) and 2 big bluestem varieties (Andropogon gerardii Vitman; Prairie view and Southlow), 4 nitrogen fertilization rates (0, 40, 80, and 160 kg N ha^-1) and 2 harvest timings (fall vs. spring harvest).   Plots were harvested in the fall of 2009 and spring of 2010.  Results were analysed to compare yield response, elemental nutrient concentration in leaves and stems, stand establishment and size.  Miscanthus, switchgrass and big bluestem all responded significantly to N fertilizer application for both the fall and spring harvest timings.  The effect of the nitrogen on N, P and K tissue concentration and removal will be presented.