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Xionghui J.,Hunan Academy of Agriculture Science | Xionghui J.,Key Laboratory of Agri Environment in Midstream of Yangtze Plain | Jiamei W.,Hunan Academy of Agriculture Science | Jiamei W.,Key Laboratory of Agri Environment in Midstream of Yangtze Plain | And 12 more authors.
Journal of the Science of Food and Agriculture | Year: 2012

Background: Soil organic carbon (SOC) sequestration, methane emission, and the net carbon sink represented by rice straw incorporated into soil (RIS) were studied using long-term experimentation with rice straw incorporated into soil (LRIS) and short-term experimentation with different patterns of rice straw incorporated into soil (SPRIS). Results: Soil organic carbon could be improved by RIS combined with soil ploughing. The increased rate of SOC deposition per cultivated layer was 0.10 t C ha -1 for 2.625 t ha -1 straw incorporated each season in LRIS and 0.36 t C ha -1 for 4.5 t straw ha -1 season -1 incorporated in SPRIS; the apparent SOC conversion by rice straw (stubble) was reduced as the amount of incorporated straw increased. However, RIS methane emission from paddy fields also significantly exacerbated the CH 4 emission flux observed during the early and late rice growing seasons, which was increased by 75.0% (P < 0.01) and 251.5% (P < 0.01), respectively, compared with combined application of nitrogen, phosphorus and potassium fertiliser (NPK). The apparent methane conversion of straw was almost uniform with a similar rice yield and soil cultivating mode. Among the patterns of RIS, methane emission was significantly reduced under straw covering untilled land, and this property led to the lowest apparent methane conversion. Conclusion: RIS with ploughing and tilling resulted in negative carbon sequestration because of increased methane emissions. A combined NPK application with only rice stubble incorporation may be sustainable for a higher rice yield, but this approach has a reduced rate of negative carbon sequestration in the paddy field. Straw covering with no tillage was the best measure to realise high yield and low carbon emission for RIS. © 2012 Society of Chemical Industry.

Wu J.M.,Central South University | Wu J.M.,Key Laboratory of Agri Environment in Midstream of Yangtze Plain | Wu J.M.,Institute of Soil and Fertilizer in Hunan Province | Ji X.H.,Key Laboratory of Agri Environment in Midstream of Yangtze Plain | And 6 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2013

Application of organic manure increases methane emissions from rice paddy fields by increasing soil organic matter. Soil organic carbon is one of the key substrates that affect methane emission from paddy soils. Different methods of researching organic carbon have been used by different researchers which have led to different conclusions regarding correlations between organic carbon and methane emission from paddy soils. To define how methane emission is influenced by fractions of soil organic carbon, a paddy field experiment with application of different exogenous organic carbon (rice straw + chemical fertilizer, chicken manure + chemical fertilizer and pig manure + chemical fertilizer) was used to monitor and analyze methane emission, changes in organic carbon fractions and their correlation. A week after application of organic manure, rice straw +chemical fertilizer (RS) and chicken manure + chemical fertilizer (CM) showed emission peaks of 221. 6 and 128. 2 mg·m-2·h-1, respectively. The methane emission was mainly concentrated before the heading stage. The amount of methane emitted in the growing season following the chemical fertilizer (CF) treatment was 296. 0 kg/hm2 and following the pig manure + chemical fertilizer (PM), CM, and RS treatments were 340. 7, 493. 6 and 794. 8 kg/hm2, respectively. There was no significant difference in methane emissions between the PM and CF treatments, while emissions from the CM and RS treatments were 1. 67 times (P < 0. 05) and 2. 69 times (P < 0. 05) higher than from the CF treatment, respectively. Amounts of methane emission and the content of oxidizable organic carbon in the paddy soil followed the same order: RS > CM > PM > CF and no fertilizers. The content of organic C fractions followed the order: fraction 1 (organic C oxidizable by 33 mmol/L KMnO4) > fraction 2 (the difference in C oxidizable by 167 mmol/L and that by 33 mmol/L KMnO4) > fraction 3 (the difference in C oxidizable by 333 mmol/L and that by 167 mmol/L KMnO4). Fraction 1 was the highest proportion of the easily oxidizable organic carbon at 42. 7% - 65%; followed by fraction 2 at 23. 3% - 48. 9%; and fraction 3 was the smallest at 2. 7% - 17. 1%. Fractions 1 and 2 in the tilling stage were higher than in the other stages in rice growth, and were a minimum in the mature rice. Fraction 1 in the rice growing season showed the same trend with methane emission as the RS and CM treatments, being obviously higher than the CF and no fertilizer treatments. Results of path analysis showed that, for fraction 1, the direct path coefficient and correlation coefficient were extremely significant at 1. 0381 and 0. 6709, respectively, whereas the direct path coefficients of fraction 2 and fraction 3 had negative values. Among all the organic carbon fractions, fraction 1was directly related to methane emission, while the other organic carbon fractions were only indirectly related to methane emission through fraction 1 during the later growth stages of rice, and the emission amounts were lower. Taken together, our results show that fraction 1 of the oxidizable organic carbon was the primary substrate of methane emission. Effective measures causing a decline in fraction 1 as a proportion of oxidation organic carbon in fertilizer resources and soil are possible key technologies for mitigating methane emissions from paddy fields.

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