Evaluation of CO₂ fluxes from an agricultural field using a process-based numerical model
2008
Buchner, Jens S. | Šimůnek, Jiří | Lee, Juhwan | Rolston, Dennis E. | Hopmans, J. W. (Jan W) | King, Amy P. | Six, Johan
During 2004, soil CO₂ fluxes, and meteorological and soil variables were measured at multiple locations in a 30-ha agricultural field in the Sacramento Valley, California, to evaluate the effects of different tillage practices on CO₂ emissions at the field scale. Field scale CO₂ fluxes were then evaluated using the one-dimensional process-based SOILCO2 module of the HYDRUS-1D software package. This model simulates dynamic interactions between soil water contents, temperature, and soil respiration by numerically solving partial-differential water flow (Richards) and heat and CO₂ transport (convection-dispersion) equations using the finite element method. The model assumes that the overall CO₂ production in the soil profile is the sum of soil and plant respiration, whose optimal values are affected by time, depth, water content, temperature, and CO₂ concentration in the soil profile. The effect of each variable is introduced using various reduction functions that multiply the optimal soil CO₂ production. Our results show that the numerical model could predict CO₂ fluxes across the soil surface reasonably well using soil hydraulic parameters determined from textural characteristics and the HYDRUS-1D software default values for heat transport, CO₂ transport and production parameters without any additional calibration. An uncertainty analysis was performed to quantify the effects of input parameters and soil heterogeneity on predicted soil water contents and CO₂ fluxes. Both simulated volumetric water contents and surface CO₂ fluxes show a significant dependency on soil hydraulic properties.
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