Agronomy and Horticulture Department


Date of this Version



The Proceedings of the International Plant Nutrition Colloquium XVI, Department of Plant Sciences, UC Davis, UC Davis


Switchgrass (Panicum virgatum L.) has been targeted for cellulosic ethanol production. Our objective was to evaluate effects of location, harvest system, and N fertilizer rates on switchgrass biomass yield and N, P, and K removal. Randomized complete block experiments with four replications were established on one-year old stands of ‘Alamo’ switchgrass at two Oklahoma locations in 2008. Harvest system and N rate interactions affected total annual yield. Biomass yields ranged from 9020 to 10530 kg/ha across harvest systems when no N was applied. With application of 179 kg N/ha, biomass yields averaged 10715, 13912, and 16516 kg/ha when harvested at seed maturity (October), after a killing frost (December), and twice per year at boot stage (July) and after a killing frost, respectively. Nutrient removal tended to increase with N fertilization and was generally twice as great for each nutrient within the two-cut system relative to the one-cut systems. When 179 kg N/ha was applied, N removal was 198, 82, and 122 kg N/ ha when cut twice, cut once at seed maturity, and cut once after frost, respectively. Phosphorus removal was 22, 12, and 11 kg/ha among these systems, respectively. Corresponding K removal was 203, 62, and 25 kg/ha. Applying N and harvesting once after frost ensures both high biomass production and reduces soil nutrient mining. Total biomass harvest, however, was greatest under the two-cut system, enabling a potential use of switchgrass early in the season for forage and availability of regrowth for bioenergy purposes.