Daycent Simulation of Methane Emissions, Grain Yield, and Soil Organic Carbon in a Subtropical Paddy Rice System

Abstract

ABSTRACT:The DayCent ecosystem model, widely tested in upland agroecosystems, was recently updated to simulate waterlogged soils. We evaluated the new version in a paddy rice experiment in Southern Brazil. DayCent was used to simulate rice yield, soil organic carbon (SOC), and soil CH 4 fluxes. Model calibration was conducted with a multiple-year dataset from the conventional tillage treatment, followed by a validation phase with data from the no-tillage treatment. Model performance was assessed with statistics commonly used in modeling studies: root mean square error (RMSE), model efficiency (EF), and mean difference (M). In general, DayCent slightly underestimated rice yields under no-tillage (by 0.07 Mg ha -1 , or 9.2 %) and slightly overestimated soil C stocks, especially in the first years of the experiment. A comparison of observed and simulated CH 4 daily fluxes showed that DayCent could simulate the general patterns of soil CH 4 fluxes with slight discrepancies. Daily soil CH 4 fluxes were overestimated by 0.43 kg ha -1 day -1 (12 %). Growth-season CH 4 emissions under no-tillage were also somewhat overestimated (11 % or 45.29 kg ha -1). We conclude that DayCent simulated SOC, rice yield, and CH 4 with some inaccuracies, but the overall performance was considered adequate. However, the model failed to represent the observed potential of no-tillage to mitigate CH 4 emissions, possibly because model algorithms could not capture the actual field conditions derived from no-tillage management, such as soil redox potential, plant senescence, and surface placement of plant residue.

Modelling greenhouse gas emissions and mitigation potentials in fertilized paddy rice fields in Bangladesh

“…The Eh in soil changes based on the flooded or drainage conditions. Continuous flooding, whether by rainfall, irrigation or both, would be a FLOD 2 period in the model schedule, with maximum Eh of -250 mV (Cheng et al, 2013, Weiler et al, 2018. The water conditions under rainfall do not saturate in the model, therefore fixed values (-20 mV) were indicated as FLOD 1.…”

“…Eh approximations are specific to the methane model. Further development of the Eh algorithm was suggested by Weiler et al, (2018), where they found contrasting results between simulated and observed CH4 emissions in flood-irrigated rice paddy fields under no tillage in southern Brazil. Soil water and gas filled pore space in the current version are normal inputs to the N2O emissions, but are not currently considered in the methane Eh equations.…”

“…For this study, we selected the DayCent model (Parton et al, 1998) which has recently had a methanogenesis sub-model added. Early studies with this version showed adequate model performance in simulating trends in SOC content and CH4 fluxes in agricultural regions -in China (Cheng et al, 2013(Cheng et al, , 2014 and Brazil (Weiler et al, 2018). The DayCent was also applied in Bangladesh rice croplands to determine SOC sequestration potential at site level (Begum et al, 2018b) and the GHG mitigation potential in regional scale (Begum et al, 2018a).…”

Intensification and diversification of degraded pasture areas in Brazil: potential of soil C accumulation and mitigation of the climate changes

“…This finding is in accordance with other studies conducted with the DayCent model under different agricultural management systems (Del Grosso et al, 2001;Del Grosso et al, 2008;Smith et al, 2012;Begum et al, 2018;Weiler et al, 2019). As was also observed by Oliveira et al (2017) and Weiler et al (2018), the model modified in this study overestimated the soil C and N stocks. However, this result is considered acceptable considering the complexity of the management systems evaluated in these studies.…”