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Title:   Author  item
                                            MAHARJAN, BIJESH - University Of Minnesotaitem
                                            Venterea, Rodney

                                                         - *Rod*
  Submitted to: Soil Biology and Biochemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 7/26/2013
                                    Publication  Date: 8/26/2013
                                    Publication URL: http://handle.nal.usda.gov/10113/57515Citation: Maharjan, B., Venterea, R.T. 2013. Nitrite intensity explains N management effects on N2O emissions in maize. Soil Biology and Biochemistry. 66:229-238.Interpretive Summary: Increasing use of N fertilizers and manures in agriculture has been contributing to rising atmospheric levels of the potent ozone depleting and greenhouse gas nitrous oxide (N2O). It is typically assumed that N2O emissions from soil depend on soil concentrations of ammonium and/or nitrate. In contrast, soil nitrite levels are seldom measured separately from nitrate in despite of its role as a central substrate in N2O production. We examined the effects of three N fertilizer sources and two placement methods on N2O and soil N levels in corn over two growing seasons. Cumulative N2O emissions were well-correlated with nitrite intensity (NO2I) but not with intensities of nitrate (NO3I) or ammonium (NH4I). By itself, NO2I explained more than 44% of the overall variance in N2O emissions. The pattern of treatment effects on N2O and NO2I were similar. When conventional urea (U) was applied using mid-row banding (MRB), both N2O and NO2I increased by a factor of about 2 compared to broadcast/ incorporated (BI). When polymer-coated urea (PCU) was the N source, MRB placement increased both N2O and NO2I compared to BI only in the wetter of the two years. When urea with microbial inhibitors (IU) was the N source, N2O and NO2I were lowest across both years and were less affected by placement than U or PCU. In the wetter year, for a subset of data including only the BI treatments, NO2I and NO3I considered as separate variables explained more of the variance then using their combined intensities. Thus, our results show that practices which reduce nitrite accumulation have the potential to also reduce N2O emissions, and that separate consideration of nitrate and nitrite dynamics can provide more insight than their combined dynamics as typically quantified. These results will be useful to scientists conducting research to better understand the sources of N2O emissions in soils and to farmers and resource managers in their efforts to reduce N2O emissions.
                                Technical Abstract: It is typically assumed that the dependence of nitrous oxide (N2O) emissions on soil nitrogen (N) availability is best quantified in terms of ammonium (NH4+) and/or nitrate (NO3-) concentrations. In contrast, nitrite (NO2-) is seldom measured separately from NO3- despite its role as a central substrate in N2O production. We examined the effects of three N fertilizer sources and two placement methods on N2O and N dynamics in maize over two growing seasons. Cumulative N2O emissions were well-correlated with NO2- intensity (NO2I) but not with NO3- (NO3I) or NH4+ (NH4I) intensity. By itself, NO2I explained more than 44% of the overall variance in cumulative N2O emissions. The pattern of treatment effects on N2O and NO2I were similar. When conventional urea (U) was applied using mid-row banding (MRB), both N2O and NO2I increased by a factor of about 2 compared to broadcast/ incorporated (BI). When polymer-coated urea (PCU) was the N source, MRB placement increased both N2O and NO2I compared to BI only in the wetter of the two years. When urea with microbial inhibitors (IU) was the N source, N2O and NO2I were lowest across both years and were less affected by placement than U or PCU. In the wetter year, for a subset of data including only the BI treatments, NO2I and NO3I considered as separate variables explained more of the variance then using their combined intensities. Thus, our results show that practices which reduce NO2- accumulation have the potential to also reduce N2O emissions, and that separate consideration of NO3- and NO2- dynamics can provide more insight than their combined dynamics as typically quantified.


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