Tim J Foster, Agronomy Department, Kansas State University, Manhattan, KS and David B. Mengel, Department of Agronomy, Kansas State University, Randolph, KS
Several tools are available to wheat producers to reduce N losses by leaching and denitrification. Applying N as close as possible to the time of uptake by the plant is one commonly used tool to avoid N loss. Another strategy is the use of nitrification inhibitors (NI) with ammonium N sources such as anhydrous ammonia (AA). Maintaining N in the ammonium form by reducing nitrification can help reduce leaching and denitrification. This project was conducted during the 2011-2012 and 2012-2013 winter wheat growth seasons, at three locations in Kansas on soils differing in both denitrification and leaching potential. The study compared the effectiveness of fall preplant AA with/without NI to the traditional practice of spring topdressing with urea as methods of applying N to winter wheat. Fall and winter precipitation varied widely between the locations, resulting in variable N use and yield. Minimal losses from fall ammonia were seen at Manhattan in 2012 and 2013, as indicated by high N recovery. Recovery was lower with topdress urea. Similar trends were observed at Ottawa in 2013, with no differences in yield or N use seen at Ottawa in 2012 between N application systems. At the sandier Kansas River Valley site, yield and N uptake were severely impacted by disease in 2012. In 2013, the Silver Lake site showed similar, high levels of N use from both fall AA and spring urea.