Nitrous oxide emissions in Midwest US maize production vary widely with band-injected N fertilizer rates, timing and nitrapyrin presence

Nitrification inhibitors have the potential to reduce N _2 O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N _2 O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N _2 O fluxes and (ii) identify UAN treatment combinations that both reduce N _2 O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha ^−1 ), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N _2 O–N emissions ( Q _10 corrected) were 0.81, 1.83 and 3.52 kg N _2 O–N ha ^−1 for the rates of 0, 90 and 180 kg N ha ^−1 , respectively; 1.80 and 2.31 kg N _2 O–N ha ^−1 for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N _2 O–N ha ^−1 for with and without nitrapyrin, respectively. Yield-scaled N _2 O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N _2 O–N Mg grain ^−1 for the 0, 90 and 180 kg N ha ^−1 rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N _2 O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing

Mean separations for the year and treatment effects on daily N₂O–N fluxes

<p><b>Table 1.</b>  Mean separations for the year and treatment effects on daily N₂O–N fluxes. The analysis was performed on lnN₂O–N, and the data presented here are the back-transformed results. Different letters indicate statistically significant differences (LSD 5%). ANOVA summary is pertinent for the treatment effects on lnN₂O–N daily fluxes for years 2010, 2011 and both years pooled together. (Notes: ,, significant at 0.05, 0.01 and 0.001 probability levels, respectively.) </p> <p><strong>Abstract</strong></p> <p>Nitrification inhibitors have the potential to reduce N₂O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N₂O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N₂O fluxes and (ii) identify UAN treatment combinations that both reduce N₂O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha⁻¹), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N₂O–N emissions (<em>Q</em>₁₀ corrected) were 0.81, 1.83 and 3.52 kg N₂O–N ha⁻¹ for the rates of 0, 90 and 180 kg N ha⁻¹, respectively; 1.80 and 2.31 kg N₂O–N ha⁻¹ for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N₂O–N ha⁻¹ for with and without nitrapyrin, respectively. Yield-scaled N₂O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N₂O–N Mg grain⁻¹ for the 0, 90 and 180 kg N ha⁻¹ rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N₂O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.</p

Weather characterization for the experimental site for years 2010, 2011 and normal data from the 30 year series 1981–2010

<p><b>Table 5.</b>  Weather characterization for the experimental site for years 2010, 2011 and normal data from the 30 year series 1981–2010. Precipitation (pp) in millimeters (mm) and mean temperature (temp.) in degrees centigrade (° C). </p> <p><strong>Abstract</strong></p> <p>Nitrification inhibitors have the potential to reduce N₂O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N₂O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N₂O fluxes and (ii) identify UAN treatment combinations that both reduce N₂O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha⁻¹), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N₂O–N emissions (<em>Q</em>₁₀ corrected) were 0.81, 1.83 and 3.52 kg N₂O–N ha⁻¹ for the rates of 0, 90 and 180 kg N ha⁻¹, respectively; 1.80 and 2.31 kg N₂O–N ha⁻¹ for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N₂O–N ha⁻¹ for with and without nitrapyrin, respectively. Yield-scaled N₂O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N₂O–N Mg grain⁻¹ for the 0, 90 and 180 kg N ha⁻¹ rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N₂O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.</p

Mean separation for the main-factor effects on N₂O–N cumulative emissions for the 2010 and 2011 growing seasons (118 and 97 d, respectively)

<p><b>Table 3.</b>  Mean separation for the main-factor effects on N₂O–N cumulative emissions for the 2010 and 2011 growing seasons (118 and 97 d, respectively). Different letters indicate statistically significant differences at Scheffe-5%. </p> <p><strong>Abstract</strong></p> <p>Nitrification inhibitors have the potential to reduce N₂O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N₂O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N₂O fluxes and (ii) identify UAN treatment combinations that both reduce N₂O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha⁻¹), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N₂O–N emissions (<em>Q</em>₁₀ corrected) were 0.81, 1.83 and 3.52 kg N₂O–N ha⁻¹ for the rates of 0, 90 and 180 kg N ha⁻¹, respectively; 1.80 and 2.31 kg N₂O–N ha⁻¹ for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N₂O–N ha⁻¹ for with and without nitrapyrin, respectively. Yield-scaled N₂O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N₂O–N Mg grain⁻¹ for the 0, 90 and 180 kg N ha⁻¹ rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N₂O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.</p

Mean separations for the significant individual and combined year and treatment interaction effects on daily N₂O–N

<p><b>Table 2.</b>  Mean separations for the significant individual and combined year and treatment interaction effects on daily N₂O–N. The analysis was performed on lnN₂O–N, and the data presented here are the back-transformed results. Different letters indicate statistically significant differences (LSD 5%). Without inhibitor (wo/I), and with inhibitor (w/I). </p> <p><strong>Abstract</strong></p> <p>Nitrification inhibitors have the potential to reduce N₂O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N₂O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N₂O fluxes and (ii) identify UAN treatment combinations that both reduce N₂O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha⁻¹), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N₂O–N emissions (<em>Q</em>₁₀ corrected) were 0.81, 1.83 and 3.52 kg N₂O–N ha⁻¹ for the rates of 0, 90 and 180 kg N ha⁻¹, respectively; 1.80 and 2.31 kg N₂O–N ha⁻¹ for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N₂O–N ha⁻¹ for with and without nitrapyrin, respectively. Yield-scaled N₂O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N₂O–N Mg grain⁻¹ for the 0, 90 and 180 kg N ha⁻¹ rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N₂O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.</p

Treatment mean separations for grain yield (GY), and yield-scaled N₂O–N

<p><b>Table 4.</b>  Treatment mean separations for grain yield (GY), and yield-scaled N₂O–N. Means presented in this table are obtained from the back-transformed data for yield-scaled means. Pre-emergence (Pre), and side-dress (Side). Different letters indicate statistically significant differences within columns (Scheffe-5%). <em>p</em>-values for each variable are included at the bottom of the table. (Notes: ,, significant at 0.05, 0.01 and 0.001 probability levels, respectively.) </p> <p><strong>Abstract</strong></p> <p>Nitrification inhibitors have the potential to reduce N₂O emissions from maize fields, but optimal results may depend on deployment of integrated N fertilizer management systems that increase yields achieved per unit of N₂O lost. A new micro-encapsulated formulation of nitrapyrin for liquid N fertilizers became available to US farmers in 2010. Our research objectives were to (i) assess the impacts of urea–ammonium nitrate (UAN) management practices (timing, rate and nitrification inhibitor) and environmental variables on growing-season N₂O fluxes and (ii) identify UAN treatment combinations that both reduce N₂O emissions and optimize maize productivity. Field experiments near West Lafayette, Indiana in 2010 and 2011 examined three N rates (0, 90 and 180 kg N ha⁻¹), two timings (pre-emergence and side-dress) and presence or absence of nitrapyrin. Mean cumulative N₂O–N emissions (<em>Q</em>₁₀ corrected) were 0.81, 1.83 and 3.52 kg N₂O–N ha⁻¹ for the rates of 0, 90 and 180 kg N ha⁻¹, respectively; 1.80 and 2.31 kg N₂O–N ha⁻¹ for pre-emergence and side-dress timings, respectively; and 1.77 versus 2.34 kg N₂O–N ha⁻¹ for with and without nitrapyrin, respectively. Yield-scaled N₂O–N emissions increased with N rates as anticipated (averaging 167, 204 and 328 g N₂O–N Mg grain⁻¹ for the 0, 90 and 180 kg N ha⁻¹ rates), but were 22% greater with the side-dress timing than the pre-emergence timing (when averaged across N rates and inhibitor treatments) because of environmental conditions following later applications. Overall yield-scaled N₂O–N emissions were 22% lower with nitrapyrin than without the inhibitor, but these did not interact with N rate or timing.</p