Nitrous oxide emissions from cultivated black soil: A case study in Northeast China and global estimates using empirical model

Manure application is effective in promoting soil carbon sequestration, but its impact on N2O emission is not well understood. A field experiment was conducted in a maize-cultivated black soil in Northeast China with six treatments: inorganic fertilizer (NPK), 75% inorganic fertilizer N plus 25% pig (PM1) or chicken (CM1) manure N, 50% inorganic fertilizer N plus 50% pig (PM2) or chicken (CM2) manure N, and no N fertilizer (CK). Annual N2O emission significantly increased from 0.34 kgNha 1 for CK to 0.86 kgNha 1 for NPK and further to 1.65, 1.02, 1.17, and 0.93 kgNha 1 for PM1, CM1, PM2, and CM2, respectively. A N tracing study showed that 71–79% of total N2O was related to nitrification at 30–70% water-filled pore space (WFPS), and heterotrophic nitrification contributed 49% and 25% to total N2O at 30% and 70% WFPS, respectively. In an incubation, N2O emission was only stimulated when nitrate and glucose were applied together at 60% WFPS, indicating that denitrification was carbon limited. PM had a stronger effect on denitrification than CM due to higher decomposability, and the lower N2O emission at higher manure application rate was associated with decreased mineral N supply. After compiling a worldwide database and establishing an empirical model that related N2O emissions (kgNha ) to precipitation (Pr, m) and fertilizer N application rate (Nr, kg N ha ) (N2O = 1.533Pr + 0.0238PrNr), annual N2O emission from global-cultivated black soil applied with inorganic fertilizer N was estimated as 347 Gg N. Our results suggested that N2O emission from cultivated black soils in China was low primarily due to low precipitation and labile organic carbon availability, and would be stimulated by manure application; thus, increased N2O emission should be taken into consideration as applying manure increases soil organic carbon sequestration.