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>Methane and Nitrous Oxide Emissions from Rice-Duck and Rice-Fish Complex Ecosystems and the Evaluation of Their Economic Significance
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Methane and Nitrous Oxide Emissions from Rice-Duck and Rice-Fish Complex Ecosystems and the Evaluation of Their Economic Significance
Rice-duck (RD) and rice-fish (RF) ecological systems are major complex planting and breeding models of rice paddy fields in southern China. Studying the methane (CH4) and nitrous oxide (N2O) emissions and their economic value from these two ecosystems can provide theoretical and practical basis for further development and utilization of these classical agricultural techniques. CH4 and N2O emissions from RD and RF ecological systems were measured in situ by using static chambers technique. Using global warming potentials (GWPs), we assessed the greenhouse effect of CH4 and N2O and their economic value. Results showed that the peaks of CH4 emission fluxes from RD and RF appeared at full tillering stage and at heading stage, and the average emission fluxes were significantly (P < 0.05) lower than that from CK. N2O fluxes remained low when the field is flooded and high after draining the water. Compared with CK, the total amount of N2O emissions was significantly (P < 0.05) higher and slightly lower than those from RD and RF, respectively. In 2006 and 2007, the total greenhouse effect of CH4 and N2O from RD and RF were 4 728.3 and 4 611 kg CO2 ha-1, 4 545 and 4 754.3 kg CO2 ha-1, respectively. The costs of greenhouse effect were 970.89 and 946.81 RMB yuan ha-1, and 933.25 and 976.23 RMB yuan ha-1, respectively, which were significant lower than those from CK (5 997.6 and 5 391.5 RMB yuan ha-1). Except for the environment cost of CH4 and N2O, the economic benefits from RD and RF were 2 210.64 and 4 881.92 RMB yuan ha-1; 3 798.37 and 5 310.64 RMB yuan ha-1, respectively, higher than those from CK. Therefore, RD and RF complex ecological planting and breeding models can effectively decrease and control CH4 and N2O emissions, and they are two of the effective strategies to reduce greenhouse gases from rice paddy fields and contribute in alleviating global warming. Thus, their adoption is important to the environment together with their economy benefits.
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