Abstract
Double rice (DR) and upland crop-single rice (UR) systems are the major rice-based cropping systems in China, yet differences in net global warming potential (NGWP) and greenhouse gas intensity (GHGI) between the two systems are poorly documented. Accordingly, a 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions and changes in soil organic carbon (SOC) in oil rape-rice-rice and wheat-rice (representing DR and UR, respectively) systems with straw incorporation (0, 3 and 6 t/ha) during the rice-growing seasons. Compared with the UR system, the annual CH4, N2O, grain yield and NGWP were significantly increased in the DR system, though little effect on SOC sequestration or GHGI was observed without straw incorporation. Straw incorporation increased CH4 emission and SOC sequestration but had no significant effect on N2O emission in both systems. Averaged over the three study years, straw incorporation had no significant effect on NGWP and GHGI in the UR system, whereas these parameters were greatly increased in the DR system, i.e., by 108% (3 t/ha) and 180% (6 t/ha) for NGWP and 103% (3 t/ha) and 168% (6 t/ha) for GHGI.
Highlights
Individual field studies have reported variable CH4 emissions among cropping systems[12,13]
It is apparent that the annual N2O emissions were significantly increased in the DR system relative to the UR system (Table 3)
Annual N2O emissions were significantly increased in the DR system, which is not in agreement with the results of previous pot experiments[16]
Summary
Individual field studies have reported variable CH4 emissions among cropping systems[12,13]. The mechanism by which straw addition affects carbon sequestration as well as CH4 and N2O emissions and GHGI in different rice cropping systems remains unknown. We hypothesize that (1) different rice cropping systems may differ greatly in CH4 and N2O emissions due to drastic flooding periods and (2) straw incorporation may result in different influences on CH4 and N2O emissions from different rice cropping systems. To test these hypotheses, a field experiment was established to measure CH4 and N2O emissions and SOC changes between the two major rice cropping systems in China. The objectives were to gain insight into the differences in grain yield, NGWP and GHGI between UR and DR systems as affected by straw application
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