Development of Fertilizer Recommendations for Big Bluestem and Switchgrass as Bioenergy Crops.

Bioenergy crops are of recent interest owing to their potential as a renewable energy source.  Perennial grasses have been investigated as a potential source of biomass.  Information on nutrient management for these crops in the southeastern U.S. is deficient.  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) fertilization.  The experiment was conducted near Brewton, AL on the southeastern coastal plain from 2007 to 2009.  Different levels of N, P, and K fertilizer were applied to a split-plot randomized complete block design.  Dry matter yield displayed a positive response to N but not P or K fertilization.  Rates of maximum agronomic yield were calculated to be 155 and 161 kg N ha^-1 for big bluestem and switchgrass, respectively.  Net return was modeled for N treatments and two biomass prices.  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.  Nutrient concentration for N treatments was modeled across time 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 enough.  This study suggests only N fertilization at a rate of 150 kg N ha^-1 is needed to acquire maximum yield in both species.