Effects of Straw Incorporation Years and Water-Saving Irrigation on Greenhouse Gas Emissions from Paddy Fields in Cold Region of Northeast China

Straw incorporation has a variety of impacts on greenhouse gas (GHG) emissions. However, few studies have focused on the effects of multi-year straw incorporation. In this study, a field experiment was established to study the effects of straw incorporation and water-saving irrigation on GHG emissions in the cold region of Northeast China. The following four treatments were included: (i) controlled irrigation (CI) with 1-year straw incorporation (C1), (ii) controlled irrigation with 5-year straw incorporation (C5), (iii) flooded irrigation (FI) with 1-year straw incorporation (F1), and (iv) flooded irrigation with 5-year straw incorporation (F5). The fluxes of N2O, CO2, and CH4 were measured by the static chamber–gas chromatography method, and their global warming potential (GWP) and greenhouse gas intensity (GHGI) in units of CO2-equivalent at the 100-year scale were calculated. The results showed that the 5-year straw incorporation reduced N2O emissions but increased CH4 emissions. Compared with C1 and F1, C5 and F5 reduced N2O emissions by 73.1% and 44.9%, respectively, while increasing the CH4 emissions by 101.7 and 195.8%, respectively. Under different irrigation regimes, CI reduced CH4 emissions by 50.4–79.7% while increasing CO2 emissions by 8.2–44.9% compared with FI. The contribution of N2O and CO2 emissions were relatively high at the mature and milk stages, respectively, with a range of 16–54% and 41–52% for the treatments. In contrast, CH4 emissions were mainly manifested at the tillering stage, with a contribution of 36–58% for the treatments. Affected by higher CH4 emissions in FI, the GWP of CI was 1.4–47.6% lower than FI. In addition, the yield of CI was 10.0–11.5% higher than FI, which resulted in a GHGI of 11.5–52.4% lower than FI, with C5 being the lowest. The irrigation regime of CI combined with 5-year straw incorporation was an effective agronomic measure to increase yield and reduce GHG emissions from paddy fields in the cold region of Northeast China.