Nitrogen Management and Dynamics in Switchgrass (Panicum virgatum L.) Biomass Production.

Nitrogen Management and Dynamics in Switchgrass (Panicum virgatum L.) Biomass Production
Joshua R. Massey, Hailin Zhang, and Alsamad Aldabaa
ABSTRACT
The evaluation of switchgrass (Panicum virgatum L.) as a biomass fuel crop has shown great potential in the US, because of its ability for growth on marginal soils and in areas of land designated in conservation reserve programs.  The objectives of this study are to determine the optimum nitrogen (N) fertilization rates for biomass production of switchgrass and to investigate nutrient cycling and dynamics. Two locations, Stillwater and Haskell, OK, were used for the N calibration studies.  Eight N treatments (0, 30, 60, 90, 120,150, 180 and 210 lbs N acre^-1 as urea) with four replications in a randomized complete block design were used in both locations.  Subsamples within 120 lbs N treatment plots were hand harvested at 45 day (six week) intervals to determine nutrient concentration.  Whole plant samples were collected to observe nutrient translocation throughout the plant life cycle.  Switchgrass yields responded well with N rates at the Stillwater site (R² = 0.69), but little response was found at the Haskell site, probably due to high soil residual N (R² = 0.13).  Yields increased with time at Stillwater until October, and decreased thereafter.  At Stillwater, percentages of nitrogen, phosphorus and potassium in the aboveground harvested biomass tended to decrease with time.  Changes in macronutrient percentages in above and belowground biomass will be investigated further.  The resulting data from this research will lead to more accurate nitrogen fertilizer recommendations for switchgrass grown for biofuel and give greater insight to nitrogen movement in the plant throughout the growing season.