Abstract:

【Objective】 The rice-duck and rice-fish ecological systems are the major complex planting and breeding models of rice paddy fields in Southern China. Studying on methane and nitrous oxide emissions and their economic value from these ecosystems can provide a theoretical and practical basis for further development and utilization of these classical agricultural techniques. 【Method】 Methane and nitrous oxide emissions from rice-duck (RD) and rice-fish (RF) ecological systems were measured in situ by using static chambers technique. Using global warming potentials (GWPs), the greenhouse effects of methane and nitrous oxide and the economic value were assessed. 【Result】 Results shown that the peak of methane emission fluxes appeared at full tillering stage and complete heading stage, and the average emission fluxes from RD and RF were significant lower than that from CK. Nitrous oxide fluxes remained low in flooding irrigation and high in draining of water. Compared with CK, the total amount of nitrous oxide emissions from RD significantly higher and RF lower. In 2006 and 2007, the total greenhouse effects of methane and nitrous oxide were 4 728.3 kg CO2?hm-2 and 4 611.0 kg CO2?hm-2, 4 545.0 kg CO2?hm-2 and 4754.3 kg CO2?hm-2, respectively. So the cost of greenhouse effect was 970.89 yuan/hm2 and 946.81 yuan/hm2, 933.25 yuan/hm2 and 976.23 yuan/hm2, respectively, which were significant lower than that from CK (5 997.6 yuan/hm2 and 5 391.5 yuan/hm2). Except for the environment cost of methane and nitrous oxide, the achieved economic benefits from RD and RF were higher than that from CK (2 210.64 yuan/hm2 and 4 881.92 yuan/hm2; 3 798.37 yuan/hm2 and 5 310.64 yuan/hm2, respectively). 【Conclusion】 Rice-duck and rice-fish complex ecological planting and breeding models can effectively decrease and control methane and nitrous oxide emissions, and they are effective strategies to reduce greenhouse gas from rice paddy fields. Thus, they are worthy to be populated by farmer in view of their economic benefit.

Key words: methane emission, nitrous oxide emission, rice-duck complex ecosystem, rice-fish complex ecosystem, greenhouse effect, economic benefit