Soil Nitrogen Management Impacts on Nitrogen Dynamics and Ammonia Oxidizers in a Sweet Corn Production System.

Understanding the impacts of different systems of nitrogen (N) management in cropping systems is important for increasing N-use efficiency and enhancing the sustainability of food production. Here we examined the impacts of organic or conventional N management systems on several plant and soil parameters including the abundance of ammonia oxidizing bacteria and archaea (AOB and AOA), which play a critical in soil N mobility by mediating the first and rate limiting step of nitrification that is responsible for nitrate formation. Sweet corn was grown in plots receiving four treatments: Control (no N), ammonium sulfate at 112 (AS100) or 224 (AS200) kg N ha^-1 and poultry litter (PL) at 112 kg ha^-1. Mean crop yield was highest in 2013 for AS200 (30,000 ears ha^-1), with the greatest difference between AS200 and Control (p<0.001). Nitrification potential for PL in 2013 and 2014 was 4.2 and 3.3 mg N kg^-1 soil day^-1, with the greatest difference between PL and Control in 2014 (P=0.003). In 2013, copy numbers of the amoA gene were highest in the AS200 and PL treatments for AOB and AOA, respectively. Differences were observed for AOB between AS200 and the Control (p<0.001) and for AOA between PL and AS200 (p=0.021). AOB copy numbers were lowest for the Control. AOA had the lowest copy numbers of the amoA gene in the treatment with the greatest amount of N input, AS200. The abundance of AOB and AOA was influenced by the type and application rate of the N source, with more abundant AOB than AOA in conventional systems and vice versa in the organic (PL) and Control treatments. The differential response of AOB and AOA suggests the need for targeted approaches to maximize N use efficiency in the two systems.