Publication Date:
2015-09-20
Description:
Process-based modeling of CH 4 and N 2 O emissions from rice fields is a practical tool for conducting greenhouse gas inventories and estimating mitigation potentials of alternative practices at the scale of management and policy-making. However, the accuracy of these models in simulating CH 4 and N 2 O emissions in direct-seeded rice systems under various management practices remains a question. We empirically evaluated the DeNitrification-DeComposition (DNDC) model for estimating CH 4 and N 2 O fluxes in California rice systems. Five and nine site-year combinations were used for calibration and validation, respectively. The model was parameterized for two cultivars, M206 and Koshihikari, and able to simulate 30% and 78% of the variation in measured yields, respectively. Overall, modeled and observed seasonal CH 4 emissions were similar (R 2 = 0.85), but there was poor correspondence in fallow period CH 4 emissions, and in seasonal and fallow period N 2 O emissions. Furthermore, management effects on seasonal CH 4 emissions were highly variable and not well represented by the model (0.2-465% absolute relative deviation). Specifically, simulated CH 4 emissions were oversensitive to fertilizer N rate, but lacked sensitivity to the type of seeding system (dry- versus water-seeding) and prior fallow period straw management. Additionally, N 2 O emissions were oversensitive to fertilizer N rate and field drainage. Sensitivity analysis showed that CH 4 emissions were highly sensitive to changes in the root to total plant biomass ratio, suggesting it is a significant source of model uncertainty. These findings have implications for model-directed field research that could improve model representation of paddy soils for application at larger spatial scales.
Print ISSN:
0148-0227
Topics:
Biology
,
Geosciences
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