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Title:   Author  item
                                            Venterea, Rodney

                                                         - *Rod*item
                                            COULTER, JEFFREY - University Of Minnesotaitem
                                            Dolan, Michael
  Submitted to: Journal of Environmental Quality
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 3/28/2016
                                    Publication  Date: 5/20/2016
                                    Citation: Venterea, R.T., Coulter, J., Dolan, M.S. 2016. Evaluation of intensive '4R' strategies for decreasing N2O emissions in rainfed corn. Journal of Environmental Quality. 45:1186-1195.Interpretive Summary: The ‘4R’ approach of using the ‘right’ rate, source, timing and placement is an accepted framework for increasing crop N use efficiency.  However, modifying one 4R component by itself does not consistently reduce nitrous oxide (N2O) emissions.  Our objective was to determine if split application timing (Sp), by itself or combined with changes in N source and rate, could improve N recovery efficiency (NRE) and N surplus (NS) and decrease direct N2O emissions for corn (Zea mays L.) over two growing seasons in Minnesota.  Compared to urea (U) applied in a single application at the recommended N rate, Sp by itself did not improve NRE or NS and did not decrease N2O.  Combining Sp with microbial inhibitors and/or a 15% reduction in N rate increased NRE from 57 to >73% and decreased NS by >20 kg N ha-1.  Emissions of N2O were correlated with NS (P < 0.001) and were more strongly correlated with NS calculated from grain N (R2 = 0.61) compared to whole-plant N (r2 = 0.39).  In spite of the relationship between N2O and NS, only the most intensive combination of Sp with inhibitors and reduced N rate decreased N2O (by 20–53%).  Strategies that modify more than one 4R component may be needed to reduce direct N2O.  Practices that increase NRE may not necessarily reduce direct N2O, but may decrease total (direct plus indirect) N2O.  These findings highlight the need for improved quantification of total N losses and indirect N2O emissions from fertilized cropping systems. These results will be useful to scientists, land managers and policy-makers interested in more accurate prediction and more effective mitigation of nitrous oxide emissions from agricultural soils.
                                Technical Abstract: The ‘4R’ approach of using the ‘right’ rate, source, timing and placement is an accepted framework for increasing crop N use efficiency.  However, modifying one 4R component by itself does not consistently reduce nitrous oxide (N2O) emissions.  Our objective was to determine if split application timing (Sp), by itself or combined with changes in N source and rate, could improve N recovery efficiency (NRE) and N surplus (NS) and decrease direct N2O emissions for corn (Zea mays L.) over two growing seasons in Minnesota.  Compared to urea (U) applied in a single application at the recommended N rate, Sp by itself did not improve NRE or NS and did not decrease N2O.  Combining Sp with microbial inhibitors and/or a 15% reduction in N rate increased NRE from 57 to >73% and decreased NS by >20 kg N ha-1.  Emissions of N2O were correlated with NS (P < 0.001) and were more strongly correlated with NS calculated from grain N (R2 = 0.61) compared to whole-plant N (r2 = 0.39).  In spite of the relationship between N2O and NS, only the most intensive combination of Sp with inhibitors and reduced N rate decreased N2O (by 20–53%).  Strategies that modify more than one 4R component may be needed to reduce direct N2O.  Practices that increase NRE may not necessarily reduce direct N2O, but may decrease total (direct plus indirect) N2O.  These findings highlight the need for improved quantification of total N losses and indirect N2O emissions from fertilized cropping systems.


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