Evaluation of Ammonium Sulfate Nitrate in Virginia Snap Bean Production

Fresh-market snap beans occupy 5,500 acres in Virginia. Producers are interested in exploring sources and rates to improve N use efficiency. This trial compared five N sources (urea with dicyandiamide, ammonium nitrate, calcium nitrate, ammonium sulfate-nitrate, and urea-ammonium nitrate) at three rates.
In 2009, for spring-grown beans, urea with dicyandiamide increased yield by 25% over the control, while the other sources did not. For fall-grown beans, all N sources increased yield by 56% over the control, with an optimum N rate of 80 lb/A, and reduced symptoms of common rust (Uromyces appendiculatus). In 2010, an abnormally dry and hot summer hampered snap bean growth and as a result yields did not increase beyond 40 lb N/A. All N sources increased yields to a similar degree, except ammonium nitrate, which did not increase yields over the check. There were no responses to S applied either as gypsum or as ammonium sulfate-nitrate. In 2011, dry weather in May followed by an intense rainstorm in June resulted in poor yields and no response to applied N in spring beans. The fall beans responded positively to N but not to S. Ammonium sulfate-nitrate, urea, and urea with dicyandiamide produced higher yields than urea-ammonium nitrate or ammonium nitrate. Grade quality was not influenced by N source. These findings support N management decisions that optimize food yields while minimizing risk of water contamination by N on the sandy loam soils of the Chesapeake Bay watershed. VA-22F