Inorganic and Organic Nitrogen Sources to Optimize Cover Crop Biomass and Cotton Yields in Conservation Systems.

The expected benefits associated with any type of conservation system require a winter annual cover crop in the Southeast.  Maximum biomass production and subsequent benefits require additional N, however no information exists on optimal rates, sources, or time of application to maximize cover crop biomass production, or how residual effects from organic N affect cotton N requirements in a high residue conservation system.  This experiment was located at the Wiregrass Research and in Headland, on a Fuquay sand (loamy, kaolinitic, thermic Arenic Plinthic Kandiudults) during crop years 2006-2008.  Main plots for the cover crop experiment were time of application (fall vs spring), subplots were N source (commercial fertilizer, and poultry litter), and sub-subplots were N rate (0 34, 67, and 101 kg N ha^-1 as commercial fertilizer and 0, 2.2, 4.5, and 6.7 Mg ha^-1 as poultry litter on an as-sampled basis).  Sub-subplot size was 7.3 m wide and 12.2 m long.  All corresponding eight row cotton plots were split with four rows receiving 101 kg N ha^-1 at sidedress, while the other four rows were not fertilized.  Growers that choose to maximize biomass production by utilizing N fertilizer, regardless of source or rate, may benefit more from fall application.  The 101 kg N ha^-1 rate increased cotton lint yields, regardless of cover crop N rate or source, but poultry litter enhanced both cover crop biomass and cotton yields compared to commercial N.  Results indicate that poultry litter could maximize biomass, maintain yields, and decrease costly commercial N use in a conservation system.