Interannual variability of carbon dioxide circulation in paddy field soil, Sukhothai Province

Abstract

Interannual variability of soil respiration was investigated in a paddy field, Sukhothai Province in northern Thailand. The objectives of this research were to monitor the variation in soil respiration in paddy field and to evaluate both soil temperature (Ts) and soil water content (SWC) functions as predictors of soil respiration. Soil respiration was measured with closed chamber technique throughout an annual cycle in 2003. For each measurement date, soil water content was taken in the top 5 cm, using time domain reflectometry (TDR) and soil-surface temperature also was recorded in the same depth, using a temperature probe. Also soil sample from surface to 30 cm depth soil core (5 cm diameter) was collected for each measurement. Variation on SR exhibited highest in January, the later month quite steady except for the extremely high respiration rates in July, in particular dry period (528.58 mg CO[subscript 2] m[superscript -2] h[superscript -1] overall mean) from January to February and from November to December and wet period from March to October (299.12 mg CO[subscript 2] m[superscript -2] h[superscript -1]). During measurement period, Ts slightly varies but SWC large changes corresponding with rainfall pattern. For the dry period, SR rates were mainly limited by SWC. Ts is minor factor influence. Whereas, in the wet period, SR rates were poorly correlated with both Ts and SWC, however Ts also seem be the most effectors and SWC still be minor factor even though shows a bit correlation. The best fitted equations were reconstructed base on Arrhenius equation as bivariate nonlinear relationships for both of the dry and the wet period. Total annual of SR to be 2.99 kg CO[subscript 2] m[superscript -2] y[superscript -1] by using measured data and 2.89 kg CO[subscript 2] m[superscript -1] y[superscript -1] estimated by integrating the model outputs in part of the dry (1.53 kg CO[subscript 2] m[superscript -1] y[superscript -1]) and wet period (1.36 kg CO[subscript 2] m[superscript -1] y[superscript -1])