High Biomass Sorghum Production Across Tillage Systems and Nitrogen Rates.

Bioenergy production has traditionally focused on perennial crops; however, these crops require an establishment period before they can be utilized.  High biomass sorghum (Sorghum bicolor L. Moench) grown as an annual crop can be used during this establishment period, but typical yields and nutrient removal across different tillage systems and nitrogen (N) rates are not well established in the Southeast.  In 2010, an experiment was initiated across conventional and conservation tillage systems on a Compass loamy sand to determine total dry matter (TDM) production and selected nutrient uptake across six different N rates (0, 34, 67, 101, 134, 168 kg ha^-1).  The split-split plot arrangement of six N rates as main plots and tillage systems as subplots also included a photoperiod sensitive (ES 5200) and a non-photoperiod sensitive cultivar (SS1515) as sub-subplots with four replications. Total dry matter yields averaged 16.3 Mg ha^-1 (2010) and 15.4 Mg ha^-1 (2011) across N rates, tillage systems, and cultivars.  No TDM response to N was observed either growing season, but an interaction between cultivar and N rate indicated that ES 5200 did respond to the lowest N rate (34 kg ha^-1).  Nitrogen uptake was highest in 2010 (148.8 kg ha^-1) compared to 2011 (99.3 kg ha^-1), but was not consistent across tillage systems.  Phosphorus uptake for the top three N rates increased 21% compared to no N, but this was only observed for ES 5200.  Potassium uptake was 22% greater in 2010 (162.2kg ha^-1) compared to 2011 (132.8 kg ha^-1), but was inconsistent across tillage systems and sorghum cultivars.  These are only preliminary results, but we have observed increased root knot nematode (Meloidogyne incognita) numbers under the ES 5200 cultivar, which could influence subsequent TDM production and nutrient uptake.