Investigating the Effects of Biochar on Soil Water Content By Optimizing the Soil Physical Parameters of Apsim Model.

Special physical properties of biochar like higher porosity can help to improve the water dynamics in soil and consequently it can translate to higher crop performance. But before conducting any modeling exercise for determining the biochar effect on crop yield, we need to make sure that the model can simulate the biochar effect on underlying soil processes like soil moisture. In this study, we determine the expected impact of biochar on soil physical properties by optimizing soil water balance in biochar and no biochar treatments. Soil water content was measured every 30 min at 4 depths (10cm, 25cm, 42cm and 60cm) in 8 different corn plots with 2 biochar (10 Mg ha-1) and no biochar treatments in 2013 in Lewis, IA. Daily mean soil water content at 10cm depth was used for ANOVA-based global sensitivity analysis as a screening tool and 9 soil physical parameters (KS, DiffusSlope, DUL, CN2Bare, LL15, Salb, SWCON and SAT) out of 26 were selected to be optimized. We used a Bayesian approach to find the posterior distribution of all these 9 parameters for both biochar and no biochar treatments. Comparison of posterior distributions between two treatments showed approximately 15 to 30% increase in drainage upper limit in first two layers, 15% decrease in saturated hydraulic conductivity and no change in the lower limit for the biochar treatment.