Characteristics of CO2,CH4 and N2O emissions from winter-fallowed paddy fields in hilly areas of South China

摘要

With closed static chamber and modified gas chromatograph (HP5890II),the in situ measurements were made on the CO2,CH4 and N2O emissions from winter-fallowed paddy fields in the hilly areas of South China.Gas samples were taken simultaneously from the fields with and without rice stubble.The results showed that both of the fields had the peak value of CO2 flux in the later afternoon.In the fields with and without rice stubble,the CH4 flux was positive in the day time while negative in the night,and the N2O flux in the day time was 1.79 and 1.58 times as much as that in the night,respectively.The diurnal average CO2 flux in the plot with rice residue was significantly higher than that of bare plot (P＜0.05).Correlation analysis demonstrated that CO2 flux in the winter-fallowed paddy fields had significant correlations with soil temperature at a depth of 5 cm,above-ground temperature and air temperature,suggesting that temperature was the main factor affecting CO2 emission from rice fields after harvesting.During the observation time (from November 10,2003 to January 18,2004),the average CO2,CH4 and N2O fluxes in the field with rice residue were (180.69±21.21) mg/m2.h,(-0.04±0.01) and (21.26±19.31)μg/m2.h,respectively.Compared with bare fields,the CO2 flux in the field with rice residue was 13.06% higher,CH4 absorption increased by 50%,while N2O flux was 60.75% lower.It was concluded that the winter-fallowed paddy field in hilly areas of South China was the source of atmospheric CO2 and N2O,and the sink of atmospheric CH4.