Using a Process-Based Numerical Model and Simple Empirical Relationships to Evaluate CO2 Fluxes from Agricultural Soils.
Abstract
Carbon dioxide emissions from an agricultural field in the Sacramento Valley, California, were evaluated using the process-based SOILCO2 module of the HYDRUS-1D software package and a simple empirical model. CO2 fluxes, meteorological variables, soil temperatures, and water contents were measured during years 2004-2006 at multiple locations in an agricultural field, half of which had been subjected to standard tillage and the other half to minimum tillage. Furrow irrigation was applied on a regular basis. While HYDRUS-1D simulates dynamic interactions between soil water contents, temperatures, soil CO2 concentrations, and soil respiration by numerically solving partially-differential water flow (Richards), and heat and CO2 transport (convection- dispersion) equations, an empirical model is based on simple reduction functions, closely resembling the CO2 production function of SOILCO2. It is assumed in this function that overall CO2 production in the soil profile is the sum of the soil and plant respiration, optimal values of which are affected by time, depth, water contents, temperatures, soil salinity, and CO2 concentrations in the soil profile. The effect of these environmental factors is introduced using various reduction functions that multiply the optimal soil CO2 production. While in the SOILCO2 module it is assumed that CO2 is produced in the soil profile and then transported, depending mainly on water contents, toward the soil surface, an empirical model relates CO2 emissions directly to various environmental factors. It was shown that both the numerical model and the simple reduction functions could reasonably well predict the CO2 fluxes across the soil surface. Regression coefficients between measured CO2 emissions and those predicted by the numerical and simple empirical models are compared.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.H13F1654B
- Keywords:
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- 1818 Evapotranspiration;
- 1847 Modeling;
- 1865 Soils (0486);
- 1866 Soil moisture;
- 1875 Vadose zone