Nitrous Oxide Emissions Respond Differently to Mineral and Organic Nitrogen Sources in Contrasting Soil Types

The use of various animal manures for nitrogen (N) fertilization is often viewed as a viable replacement for mineral N fertilizers. However, the impacts of amendment type on N2O production may vary. In this study, N2O emissions were measured for 2 yr on two soil types with contrasting texture and carbon (C) content under a cool, humid climate. Treatments consisted of a no-N control, calcium ammonium nitrate, poultry manure, liquid cattle manure, or liquid swine manure. The N sources were surface applied and immediately incorporated at 90 kg N ha(-1) before seeding of spring wheat (Triticum aestivum L.). Cumulative N2O-N emissions from the silty clay ranged from 2.2 to 8.3 kg ha(-1) yr(-1) and were slightly lower in the control than in the fertilized plots (P = 0.067). The 2-yr mean N2O emission factors ranged from 2.0 to 4.4% of added N, with no difference among N sources. Emissions of N2O from the sandy loam soil ranged from 0.3 to 2.2 kg N2O-N ha(-1) yr-1, with higher emissions with organic than mineral N sources (P = 0.015) and the greatest emissions with poultry manure (P < 0.001). The N2O emission factor from plots amended with poultry manure was 1.8%, more than double that of the other treatments (0.3-0.9%), likely because of its high C content. On the silty clay, the yield-based N2O emissions (g N2O-N kg(-1) grain yield N) were similar between treatments, whereas on the sandy loam, they were greatest when amended with poultry manure. Our findings suggest that, compared with mineral N sources, manure application only increases soil N2O flux in soils with low C content.