Validation of the DNDC-Rice model by using CH_4 and N_2O flux data from rice cultivated in pots under alternate wetting and drying irrigation management(Environment)

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The DNDC (DeNitrification-DeComposition)-Rice model, one of the most advanced process-based models for the estimation of greenhouse gas emissions from paddy fields, has been discussed mostly in terms of the reproducibility of observed methane (CH_4) emissions from Japanese rice paddies, but the model has not yet been validated for tropical rice paddies under alternate wetting and drying (AWD) irrigation management, a water-saving technique. We validated the model by using CH_4 and nitrous oxide (N_2O) flux data from rice in pots cultivated under AWD irrigation management in a screen-house at the International Rice Research Institute (Los Banos, the Philippines). After minor modification and adjustment of the model to the experimental irrigation conditions, we calculated grain yield and straw production. The observed mean daily CH_4 fluxes from the continuous flooding (CF) and AWD pots were 4.49 and 1.22kg C ha^<-1> day^<-1>, respectively, and the observed mean daily N_2O fluxes from the pots were 0.105 and 34.1g N ha^<-1> day^<-1>, respectively. The root-mean-square errors, indicators of simulation error, of daily CH_4 fluxes from CF and AWD pots were calculated as 1.76 and 1.86kg C ha^<-1> day^<-1>, respectively, and those of daily N_2O fluxes were 2.23 and 124g N ha^<-1> day^<-1>, respectively. The simulated gross CH_4 emissions for CF and AWD from the puddling stage (2 days before transplanting) to harvest (97 days after transplanting) were 417 and 126kg C ha^<-1>, respectively; these values were 9.8% lower and 0.76% higher, respectively, than the observed values. The simulated gross N_2O emissions during the same period were 0.0279 and 1.45kg N ha^<-1> for CF and AWD, respectively; these values were respectively 87% and 29% lower than the observed values. The observed total global warming potential (GWP) of AWD resulting from the CH_4 and N_2O emissions was approximately one-third of that in the CF treatment. The simulated GWPs of both CF and AWD were close to the observed values despite the discrepancy in N_2O emissions, because N_2O emissions contributed much less than CH_4 emissions to the total GWP. These results suggest that the DNDC-Rice model can be used to estimate CH_4 emission and total GWP from tropical paddy fields under both CF and AWD conditions.
2012-06-00

Validation of the DNDC-Rice model by using CH_4 and N_2O flux data from rice cultivated in pots under alternate wetting and drying irrigation management(Environment)

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