Relationship between CH4 and N2O flux from soil and their ambient mixing ratio in a riparian rice-based agroecosystem of tropical region
2011
Temporal variations of the ambient mixing ratio of greenhouse gas (CH4 and N2O) in a riparian rice-based agro-ecosystem of tropical region were studied during 2005–2006 in coastal Odisha. The endeavour was made with the hypothesis that the ambient mixing ratio of CH4 and N2O depends on the changes in the flux of CH4 and N2O from the rice fields in the riparian rice ecosystems. A higher ambient mixing ratio of CH4 was recorded during the tillering to grain filling stages of the rice crop, during both dry and wet seasons. The higher ambient mixing ratio of CH4 during the wet season may attribute to the higher CH4 emission from the rice field. The average mixing ratio of CH4 was recorded as 1.84 ± 0.05 ppmv and 1.85 ± 0.06 ppmv during 2005 and 2006, respectively. The ambient CH4 mixing ratio was recorded negatively correlated with the average ambient temperature. The N2O mixing ratio ranged from 261.57 to 399.44 ppbv with an average of 330.57 ppbv during 2005. However, the average mixing ratio of N2O was recorded as 318.83 ± 20.00 ppbv during 2006. The N2O mixing ratio was recorded to be negatively correlated with rainfall and average ambient temperature. Significant negative correlation (r = −0.209) of N2O with sunshine hours may attribute to the photochemical break down of N2O. The temporal variation of N2O flux from the rice field does not affect the ambient mixing ratio of N2O in the same way as in the case of the ambient mixing ratio of CH4. However, the higher mixing ratio of N2O during the fallow period of the post monsoon period may attribute to the N2O flux from soil. Results indicate that intensively cultivated coastal ecosystems can be a major source of ambient greenhouse gas.
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