Nitrous oxide is one of key greenhouse gases with high global warming potential. Agricultural soil is regarded as a major source of N2O. As an effective management practice to improve soil fertility and to sequester carbon in soils, the application of organic amendments has been gaining worldwide attentions. Although the effect of organic amendments on N2O emissions from agricultural soils has been extensively studied in the past two decades, little information is available on soil N2O emissions from Mollisols in Northeast China as affected by organic amendments and chemical fertilizers. Dr. Lu-Jun Li and his group conducted a field experiment to evaluate the influences of long-term applications of organic amendments and chemical fertilizers on N2O emissions from Mollisols and to relate soil N2O fluxes to soil moisture and temperature.
Results showed that cumulative N2O emissions in the entire maize growing period were significantly (all P<0.05) increased by 66, 86 and 83% under the applications of 4.5 Mg ha–1 maize straw combined with NPK, 7.5 and 22.5 Mg ha–1 pig manure combined with NPK, respectively, compared with the control (0.64±0.01 kg N2O-N ha–1), whereas NPK fertilizer alone and 2.25 Mg ha–1 maize straw combined with NPK had no remarkable influences (P>0.05). Nonetheless, even increasing nitrogen inputs, the cumulative microbial N2O emission over 126 days had an upper threshold around 1.2 kg N2O-N ha–1. Approximately 25-44% of N2O was emitted from the applied organic amendments, and the emission factor of applied organic amendments as N2O based on 126 days was between 0.07 and 1.52%, higher than NPK fertilizer-induced EF (0.03%). Soil temperature explained 38-96% of the seasonal variation in soil N2O fluxes using exponential models, with a Q10 of 2.01-3.48.
The results suggest that the influences of organic amendments on soil N2O emissions from Mollisols primarily vary with the type of the applied organic amendments, whereas great nitrogen inputs at maximum asymptotically double baseline cumulative emissions.