Carbon Stocks Stored Above and Belowground in Switchgrass as Affected by Cultivar and Nitrogen Fertilization.

Carbon Stocks Stored Above and Belowground in Switchgrass as Affected by Cultivar and Nitrogen Fertilization Donald D. Tyler, Charles T Garten, Robin L. Graham, Julie D. Jastrow Stan D. Wullschleger, Burton C. English Switchgrass (Panicum virgatum) is a perennial, native, warm-season grass that has been chosen by the Department of Energy as a model crop for use as a cellulosic biofuel feedstock. It develops an extensive root system and has the potential to enhance above and below ground carbon storage as compared to annual row crops. Carbon stocks in 4 and 5 year old ‘Alamo’ switchgrass stands were evaluated in a cultivar study, involving three synthetic lowland ecotypes, and a nitrogen-seeding rate study. In the 4 year old cultivar study, above and below ground carbon stocks were measured three times during the growing season. Belowground roots were sampled and sorted into size fractions, and dead and live roots. At the end of the season dead roots were less than 10 % of the total root mass in the top 90 cm. The total belowground root biomass was over 500 g per m2. In the nitrogen-seeding rate study using nitrogen rates of 0, 67, 134, and 202 kg N per ha, both above and below-ground biomass increased with nitrogen fertilization and the higher nitrogen rates resulted in lower C:N ratios primarily from increasing nitrogen concentration in the root tissue. This could possibly enhance root decomposition and result in less carbon storage compared to the lowest nitrogen fertilization rate which resulted in similar above ground biomass yields as compared to the higher N rates.