Simulation of Soil Respiration at Hourly Time Step.

Improved simulation of carbon dynamics in agroecosystems can benefit from representation of sub-daily dynamics. In this study we simulate hourly soil CO2 flux by incorporating biophysical controls related to soil moisture, soil temperature and availability of soil organic carbon. In addition we incorporated the effect of root respiration driven by canopy photosynthesis. Following the conceptual framework suggested by Thornley (1970), conversion efficiency (Yg) and maintenance coefficient (m) were estimated using two years of field experiment conducted at Isfahan University of Technology, Isfahan, IRAN. The framework was then implemented into the BioCro R package (which simulates C4 photosynthesis, biomass production and plant physiological parameters at hourly time step) to account for root respiration. Coupled with soil carbon dynamics, the model explicitly separates between root-derived respiration and respiration derived from SOM decomposition due to microbial activity. The model’s output was compared with soil respiration form field experiments planted to maize conducted in Ames, USA. Preliminary results show that the cumulative soil respiration simulated by model matches better with in-row in comparison to the between rows or 1/3 of the row measurements.  It was also found that addition of root respiration to the model improves the simulation of cumulative soil respiration by lowering NRMSE by 5% and bias by 8%.