Hoben, J. P. 2009. On-farm nitrous oxide (N2O) response to nitrogen fertilizer in corn cropping systems. Thesis, Michigan State University, East Lansing, Michigan, USA..
Previous studies have indicated that large reductions in N2O emissions may be possible with relatively little impact on grain yield or economic return by better managing N fertilizer. To test this hypothesis in farm settings, experiments were conducted in Michigan at three farms and one experiment station, all planted to corn, in 2007 and in 2008. Six rates of nitrogen fertilizer (0-225 kg N ha-1) were broadcast and incorporated prior to planting. Across all sites and years, increases in N2O flux were best described by a nonlinear response to increasing N rate. Emission factors ranged from 1.4 to 3.4% and increased with increasing N application across all sites and years, especially at N rates above that required for maximum crop yield. Nitrous oxide flux increased by 43% (2.0 kg N2O-N ha-1 yr-1) and 115% (5.1 kg N2O-N ha-1 yr-1) for the 180 and 225 kg N ha-1 rates, respectively, compared with the next lowest, 135 kg N ha-1 rate, which was closer to the maximum return to N rate (MRTN). The MRTN (0.10 price ratio) of 154 kg N ha-1 yielded 8.3 Mg ha<sup-1. Application of N fertilizer at or slightly below the MRTN would have reduced total N2O flux by 79% on average. This study shows the potential to lower agricultural N2O fluxes within a range of N fertilization which does not greatly affect yield.
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