Abstract
Straw retention is a widely used method in rice planting areas throughout China. However, the combined influences of straw retention and nitrogen (N) fertilizer application on greenhouse gas (GHG) fluxes from paddy fields merits significant attention. In this work, we conducted a field experiment in the lower Yangtze River region of China to study the effects of straw retention modes and N fertilizer rates on rice yield, methane (CH4) and nitrous oxide (N2O) emission fluxes, global warming potential (GWP), and greenhouse gas intensity (GHGI) during the rice season. The experiments included six treatments: the recommended N fertilizer—240 kg N·ha−1 with (1) no straw, (2) wheat straw, (3) rice straw, and (4) both wheat and rice straw retentions; in a yearly rice–wheat cropping system (N1, WN1, RN1, and WRN1, respectively); as well as both wheat and rice straw retentions with (5) no N fertilizer and (6) 300 kg N·ha−1 conventional N fertilizer (WRN0, WRN2). The results showed that CH4 emissions were mainly concentrated in the tillering fertilizer stage and accounted for 54.2%–87.5% of the total emissions during the rice season, and N2O emissions were primarily concentrated in the panicle fertilizer stage and accounted for 46.7%–51.4% total emissions. CH4 was responsible for 87.5%–98.5% of the total CH4 and N2O GWP during the rice season, and was the main GHG contributor in the paddy field. Although straw retention reduced N2O emissions from paddy field, it significantly increased CH4 emissions, which resulted in a significant net increase in the total GWP. Compared with the N1 treatment, the total GWP of WN1, WRN1, and RN1 increased by 3.45, 3.73, and 1.62 times, respectively; and the GHGI increased by 3.00, 2.96, and 1.52 times, respectively, so the rice straw retention mode had the smallest GWP and GHGI. Under double-season’s straw retentions, N fertilizer application increased both CH4 and N2O emissions, and the WRN1 treatment not only maintained high rice yield but also significantly reduced the GWP and GHGI by 16.5% and 30.1% (p < 0.05), respectively, relative to the WRN2 treatment. Results from this study suggest that adopting the “rice straw retention + recommended N fertilizer” mode (RN1) in the rice–wheat rotation system prevalent in the lower Yangtze River region will aid in mitigating the contribution of straw retention to the greenhouse effect.
Highlights
Of global rice production, 30% comes from China, making it one of the world’s most important rice producers [1,2]
- We investigated the effects of straw retention modes and N fertilizer rates on rice yield and CH4 and N2O emissions in a rice–wheat cropping system
Under the condition of double-season’s straw retentions, the cumulative N2O emission from the rice field treated with the conventional N fertilizer rate increased by 36.4% relative to the paddy field treated with the recommended N fertilizer rate
Summary
30% comes from China, making it one of the world’s most important rice producers [1,2]. In order to improve soil quality and stabilize rice yield, in recent years, the Chinese government has promoted straw retention over large areas during the rice planting process [1,3,4]. Many studies have demonstrated that straw retention offers favorable ecological and economic benefits, such as reducing chemical fertilizer inputs, increasing soil nutrients and enzyme activities, and improving crop yields [6,7,8,9,10]. Straw retention undoubtedly produces more greenhouse gas (GHG) emissions than chemical fertilizer treatment [11,12,13]. Xing et al [21] showed that the annual N fertilizer application was up to 500–600 kg N·ha−1 in the rice–wheat cropping system along the Yangtze River region. Knowledge of how GHG emissions and rice yields respond to straw retention and N management is helpful to assess the potential of rice–wheat rotation system to sustain rice yields and mitigate GHG emissions [29]
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