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

Abstract

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 ∼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.