Modeling Biochar Effects on Soils and Crops Using Apsim.

To better understand the complex interactions that occur in the soil-plant-atmosphere continuum following biochar amendments, we modified the APSIM model to account for biochar effects on soil organic matter (SOM), CO₂ emissions, priming effects on fresh organic matter, N immobilization/mineralization, soil bulk density, soil pH, cation exchange capacity, drained upper and lower limits (DUL and LL) and saturation point. The diversity among biochar types was captured by using generic equations and biochar specific input parameters to the equations. The modified model was used to investigate the impact of different biochar parameters (sensitivity analysis) on a number of soil-plant-atmosphere variables in Iowa cropping systems using climate data form 1950-2010. Our analysis indicated that biochar effects on plant available water content (PAWC) and corn yield were larger in poor quality soils (low SOM and water holding capacity) than in high quality soils. Among the studied biochar parameters, we found that the amount of biochar applied had the greatest impact on the simulation output. The magnitude of the corn yield response to the biochar application found in this modeling study ranged from -2 to 4% and was variable among years, soils and cropping systems. Positive yield responses were caused by the increase in PAWC (up to 24% increase) and net N mineralization rates (up to 15% increase), while negative responses were caused mainly by nitrogen limitations due to priming effects, N immobilization by biochar and/or pH effects on N cycling. Model calibration and validation are in progress