Development of Fertilizer Recommendations for Big Bluestem and Switchgrass In Biomass Production.

Biomass is currently being utilized as source for renewable energy.  Perennial grasses may play a large role as a potential source of biomass.  Information on nutrient management of these crops in the Southeast is lacking.  The objective of this study was to examine the response of big bluestem (Andropogen gerardii) and switchgrass (Panicum virgatum) to different levels of nitrogen (N), phosphorus (P), and potassium (K) fertility.  The experiment was conducted near Brewton, AL on the southeastern coastal plain from 2007 to 2010.  Sixteen different levels of N, P, and K fertilizer were applied to a split-plot randomized complete block design.  Dry matter yield (DMY) displayed a positive response to N fertilization during all years while a response to P fertilization was only observed in switchgrass during 2010.  Phosphorus and K fertilization under any other scenario resulted in no change to DMY.  Rates of maximum agronomic yield were calculated to be 155 kg N ha^-1 for big bluestem and 143 kg N ha^-1 and 98 kg P₂O₅ ha^-1 for switchgrass, respectively.  Net return was modeled for N treatments and two biomass prices during 2008 and 2009.  It was observed that N fertilization increased net return in switchgrass but not big bluestem.  Removal was determined for N, P, and K treatments and luxury consumption was observed for all nutrients and species except for P in big bluestem.  Nutrient concentration for N treatments was modeled across time during 2008 and 2009 where a difference was observed between regressions lines of high and low N rates.  This indicated deficiency could be detected in these grasses if tissue samples are taken early in the growing season.  This study suggests N fertilization at a rate near 150 kg N ha^-1 in both species.  Data from 2010 indicates the need for P fertilization in switchgrass to acquire maximum yield after years of establishment.