Tillage and Nitrogen Rate Effects on Area- and Yield-Scaled Nitrous Oxide Emissions from Pre-Plant Anhydrous Ammonia

Precision-guided technologies enable corn (Zea mays L.) growers to apply pre-plant anhydrous ammonia (NH3) parallel to intended corn rows even when full-width tillage follows NH3 application. Close, but crop-safe, proximity of NH3 to corn rows may potentially increase N use efficiency and lower N requirements and nitrous oxide (N2O) emissions. Experiments in 2011 and 2012 on silty clay loam Mollisol near West Lafayette, IN, assessed area-and yield-scaled N2O emissions when spring pre-plant NH3 was applied at recommended (202 kg N ha(-1)) and reduced rate (145 kg N ha(-1)), in no-till (NT) and conventional tillage (CT) systems following NT soybean [Glycine max (L.) Merr.]. Each 12-cm deep NH3 band was positioned 15 cm from, and parallel to, intended corn rows using precision guidance. Nitrification of NH3 in application bands was 31% faster under CT than NT. Area-and grain yield-scaled N2O emissions were N rate dependent in both growing seasons. On average, CT+202 kg N resulted in highest area-scaled (mean = 2.45 kg N ha(-1)) and grain yield-scaled (mean = 360 g N Mg-1) N2O emissions. In contrast, CT+145 kg N had similar yield-scaled emissions as NT+202 and NT+145 kg N, and reduced area-scaled N2O emissions by 65, 45, and 19% respectively, relative to CT+202 kg N, NT+202 kg N, and NT+145 kg N treatments. These preliminary results suggest that reducing pre-plant NH3 rates by similar to 30% under CT has the potential to reduce N2O emissions without significant yield declines in the CT phase of a NT-CT rotation, despite faster nitrification in CT.