Modeling soil carbon and nitrogen dynamics in no-till and conventional tillage using PASTIS model

The performance of the PASTIS model was evaluated to simulate soil C and N fluxes under real field conditions with conventional moldboard plowing (CT) and no-tillage (NT) systems differentiated for 33 yr for a loamy soil in northern France. Afterward, the influences on the C and N fluxes by soil temperature, soil water content, and quantity and localization of soil organic matter (SOM) and crop residues in the soil profile were determined. The model PASTIS was able to provide good simulations for the dynamics of soil water content and temperature, CO2 emissions, residue decomposition, and N mineralization. Simulation showed that the presence of the mulch layer in NT reduced cumulative total water evaporation and increased water drainage at the bottom of the 25-cm depth. Furthermore, simulation showed that the larger cumulative total CO2 flux in NT resulted from larger CO2 emissions as a product of crop residue decomposition and not as product of SOM decomposition. The larger amount of accumulated residues of previous crops in NT more than compensated for the slower residue decomposition rate of surface compared with incorporated residues. It was the water content of the surface crop residues that largely controlled the magnitude of this difference in decomposition rate of the crop residues between CT and NT. This means that, besides the amount of crop residues in both tillage systems, the distribution of rainfall and potential evaporation have a large influence on the differences in C and N fluxes between the two tillage systems.