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 ∼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

Achieving Lower Nitrogen Balance and Higher Nitrogen Recovery Efficiency Reduces Nitrous Oxide Emissions in North America's Maize Cropping Systems

Few studies have assessed the common, yet unproven, hypothesis that an increase of plant nitrogen (N) uptake and/or recovery efficiency (NRE) will reduce nitrous oxide (N2O) emission during crop production. Understanding the relationships between N2O emissions and crop N uptake and use efficiency parameters can help inform crop N management recommendations for both efficiency and environmental goals. Analyses were conducted to determine which of several commonly used crop N uptake-derived parameters related most strongly to growing season N2O emissions under varying N management practices in North American maize systems. Nitrogen uptake-derived variables included total aboveground N uptake (TNU), grain N uptake (GNU), N recovery efficiency (NRE), net N balance (NNB) in relation to GNU [NNB(GNU)] and TNU [NNB(TNU)], and surplus N (SN). The relationship between N2O and N application rate was sigmoidal with relatively small emissions for N rates <130 kg ha−1, and a sharp increase for N rates from 130 to 220 kg ha−1; on average, N2O increased linearly by about 5 g N per kg of N applied for rates up to 220 kg ha−1. Fairly strong and significant negative relationships existed between N2O and NRE when management focused on N application rate (r2 = 0.52) or rate and timing combinations (r2 = 0.65). For every percentage point increase, N2O decreased by 13 g N ha−1 in response to N rates, and by 20 g N ha−1 for NRE changes in response to rate-by-timing treatments. However, more consistent positive relationships (R2 = 0.73–0.77) existed between N2O and NNB(TNU), NNB(GNU), and SN, regardless of rate and timing of N application; on average N2O emission increased by about 5, 7, and 8 g N, respectively, per kg increase of NNB(GNU), NNB(TNU), and SN. Neither N source nor placement influenced the relationship between N2O and NRE. Overall, our analysis indicated that a careful selection of appropriate N rate applied at the right time can both increase NRE and reduce N2O. However, N2O reduction benefits of optimum N rate-by-timing practices were achieved most consistently with management systems that reduced NNB through an increase of grain N removal or total plant N uptake relative to the total fertilizer N applied to maize. Future research assessing crop or N management effects on N2O should include N uptake parameter measurements to better understand N2O emission relationships to plant NRE and N uptake