Methane and Nitrous Oxide Emissions from Rice Field and Related Microorganism in Black Soil, Northeastern China

Methane (CH₄) and nitrous oxide (N₂O) emissions from rice field in black soil were measured in situ by using static chamber techniques during crop growth season in 2001. The experiment fields were divided into three plots for three different treatments, one with continuous flooded and applying urea (CU), one with continuous flooded and applying slow-releasing urea (CS), and one with intermittent irrigation and applying urea (IU). Under the same fertilization application, compared with continuous flooded, intermittent irrigation can significantly reduce CH₄ emission and increase N₂O emission. But, integrated global warming potentials (GWP_S) of CH₄ and N₂O emission were reduced greatly, while rice yield was not affected. So, the intermittent irrigation is an effective measure to reduce greenhouse gas emissions from paddy fields. The amount of CH₄ emission during rice-growing season for the three treatments was all much lower than that from any other region in China. There was a trade-off relationship between CH₄ and N₂O emissions. We also measured the numbers of methanogens, methanotrophs, nitrifiers and denitrifers from rice field at various growth stages in 2001. Bacteria populations were estimated by the most probable number (MPN) method. Regression analyses show CH₄ emissions were closely related to methanogens population for all the three treatments. There was a positive correlation between denitrifiers population level and N₂O emission in the treatment of IU.