Growing season N2O emissions from two-year potato rotations in a humid environment in New Brunswick, Canada

Few studies have examined the effects of crop rotation on N2O emissions. This study quantified N2O emissions from seven 2-yr potato rotations over a 3-yr period, 2008-2010, where the potato phase was present in 2008 and 2010. In addition, the potential to predict variation in cumulative growing season N2O emissions was examined using indices of nitrate availability [nitrate exposure (NE), a time integrated measure of soil nitrate concentrations in the surface soil], carbon availability (cumulative growing season CO2 emissions) and aeration [time-weighted average water-filled pore space (WFPS)]. In the potato phase of the rotations, even for treatments receiving the same fertilizer N rate (193 kg N ha(-1)), a wide range in cumulative growing season N2O emissions was measured in both 2008 and 2010 (0.39-1.49 and 0.81-2.03 kg N ha(-1), respectively). The NE explained 52 and 70% of the variation in growing season N2O emissions under potato production in 2008 and 2010, respectively. Carbon availability also had a significant effect on N2O emissions, as indicated by increased N2O emissions in rotations where residues of the preceding crop resulted in increased CO2 emissions early in the growing season. A large proportion (67%) of the variation in cumulative N2O emissions among rotation crops was also explained by NE. Choice of rotation crop resulted in an almost twofold difference (0.9-1.7 kg N ha(-1)) in N2O emissions over the 2-yr rotation cycle. Greater N2O emissions over the 2-yr rotation cycle were measured for rotation crops of soybean, Italian ryegrass, red clover and potato than for rotation crops of corn, canola and barley. However, the fertilizer N management in both the potato and rotation crop phases may be as or more important than the choice of rotation crop in influencing the risk of N2O emissions.