Emissions of nitrous oxide and carbon dioxide: influence of tillage type and nitrogen placement depth

Innovative management practices are required to increase the efficiency of N fertilizer usage and to reduce nitrous oxide (N2O) and carbon dioxide (CO,) emissions from agricultural soils. The objectives of this study were to evaluate the feasibility of using conservation tillage and N fertilizer placement depth to reduce N2O and CO2 emissions associated with corn (Zea mays L.) production on clay loam soils in Eastern Canada. A 3-yr field study was established on a wheat (Triticum aestivum L.)-corn-soybean [Glycine max (L.) Merr.] rotation with each phase of the rotation present every year. Investigations were focused on the corn phase of the rotation. The tillage treatments following winter wheat included fall moldboard plow tillage (15 cm depth), fall zone-tillage (21 cm width, 15 cm depth), and no-tillage. The N placement treatments were "shallow" placement of sidedress N (2-cm depth) and "deep" placement of sidedress N (10-cm depth). Nitrous oxide emissions were measured 53 times and CO2 emissions were measured 43 times over three growing seasons using field-based sampling chambers. There was a significant tillage and N placement interaction on N2O emissions. Averaged over all three tillage systems and site-years, N2O emissions from shallow N placement (2.83 kg N ha(-1) yr(-1)) were 26% lower than deep N placement (3.83 kg N ha(-1) yr(-1)). The N2O emissions were similar among the tillage treatments when N was placed in the soil at a shallow depth. However, when N was placed deeper in the soil (10 cm), the 3-yr average N2O emissions from zone-tillage (2.98 kg N ha(-1) yr(-1)) were 20% lower than from no-tillage (3.71 kg N ha(-1) yr(-1)) and 38% lower than those from moldboard plow tillage (4.81 kg N ha(-1) yr(-1)). Tillage type and N placement depth did not affect CO2 emissions (overall average = 5.80 Mg C ha(-1) yr(-1)). Hence, zone-tillage and shallow N placement depth reduced N2O emissions without affecting CO2 emissions.