Wheat Nitrogen Requirements Following Sunn Hemp in Alabama.

Elevated nitrogen (N) fertilizer costs have renewed interest in alternative N sources, such as legumes. Sunn hemp (Crotalaria juncea L.) is a tropical legume capable of producing considerable biomass in a short period of time.  Recent breeding efforts at Auburn University, AL have produced a sunn hemp cultivar capable of producing seed in the region that may lead to its widespread use across the Southeast. A randomized complete block design with a split-plot restriction and four replications was conducted at the Wiregrass Research and Extension Center (WGS) in Headland, AL on a Dothan sandy loam in 2008 and 2009 and at the Tennessee Valley Research and Extension Center (TVS) in Bella Mina, AL on a Rexor sandy loam in 2009.  Main plots were legume cover (sunn hemp and fallow) and subplots were N rates (0, 28, 56, 84, and 112 kg ha^-1) applied as ammonium nitrate in early to mid-February at approximately Feekes 4 to determine wheat (Triticum aestivum L.) yield production.  Average sunn hemp biomass production was 53 % greater in 2008 than 2009. In 2008, overall wheat grain yields were extremely low, but sunn hemp produced a 54 % yield increase in harvested wheat grain compared to fallow plots. Increasing N application during 2008 also resulted in reduced grain moisture and increased test weights. During the following year, there was a 58 % yield improvement in harvested wheat grain following sunn hemp when compared to the fallow treatment at WGS, but no significant differences were seen at TVS. Results from 2009 found wheat grain test weights decreased as fertilizer application increased at TVS. Future research will continue to evaluate how sunn hemp can fit into existing crop rotations across the Southeast.