Sunn Hemp As a Cover Crop to Reduce Nitrogen Inputs for Winter Wheat.

The tropical legume sunn hemp (Crotalaria juncea L.) has the potential to perform as a beneficial cover crop in the southeastern United States due to its ability to accumulate large amounts of biomass and symbiotic nitrogen (N) in a short period of time during the summer months.  Planting sunn hemp, prior to a winter cereal, such as wheat (Triticum aestivum L.) could reduce the amount of synthetic N fertilizer required for wheat production.  Treatments were arranged in a strip-plot configuration in a randomized complete block design with four replications at three locations in Alabama.  Main plots were three sunn hemp planting dates (May, June, July) compared with a fallow area, and subplots were four fall and spring N rate combinations applied to wheat fallow plots.   Sunn hemp plots only received spring applications.   Sunn hemp biomass and N content were measured and wheat yields were determined the following spring.  Sunn hemp biomass production and N content averaged 87% and 55 % higher for June and July planting compared with the May planting date.  Two of the three locations showed no difference in wheat yields between fallow and sunn hemp plots, while fallow plots yielded 30% higher than sunn hemp plots at the third location.  Differences were observed among N rate treatments across planting dates, but wheat yielded best under recommended N rates.  Current results fail to show that N from sunn hemp was successful in reducing fertilizer requirements for wheat in 2012, but an additional year of evaluation will be conducted to confirm these results.