Nitrogen and Harvest Frequency Effect on Yield and Cost for Four Perennial Grasses

A USDOE and USDA study concluded that more than 20 million U.S. hectares of cropland, idle cropland, and cropland pasture could be converted from current uses to the production of perennial grasses from which biomass could be harvested for use as biorefinery feedstock. This study was conducted to determine the most efficient species, level of N, and harvest frequency from among four perennial grass species {'Midland 99' bermudagrass [Cynodon dactylon (L.) Pers.], 'Carostan' flaccidgrass (Pennisetum flaccidum Griseb.),'SL 93-3' (a selection from 'Alamo') switchgrass (Panicum virgatum L.), and weeping lovegrass [Eragrostis curvula (Schrad.) Nees]). Each species was established in 2002 on a Kirkland silt loam soil near Stillwater, OK. Treatments in postestablishment years consisted of four N fertilization levels (34, 67, 134, and 269 kg ha(-1) yr(-1)) and two harvest systems (once year(-1) in October, and twice year(-1) in July and October). Plots were harvested in 2003, 2004, and 2005. For bermudagrass, flaccidgrass, and lovegrass, the greatest biomass yield year(-1) was produced from plots harvested twice year(-1). Switchgrass produced significantly more biomass than the other three species. Biomass yield to N response functions were estimated for switchgrass. For most biomass price and N price combinations, the optimal strategy is to establish switchgrass, and in postestablishment years, to fertilize with 65 kg N ha(-1) yr(-1) and harvest once year(-1) after senescence.