How Does Biochar Affect the Pore Size Distribution, S-Index and Saturated Hydraulic Conductivity of a Sandy Soil?.

In this study, we analyzed the effect of biochar on pore size distribution, S-index and saturated hydraulic conductivity of a sandy loam soil. An experiment was conducted by mixing hard-wood fast pyrolysis biochar with soil (0%, 3%, and 6% w/w). Then the mixed soil was placed into columns in either the bottom 11.4 cm or the top 11.4 cm to simulate deep banding in rows (DBR) and uniform topsoil mixing (UTM) applications, respectively. Four sets of 18 columns were incubated at 30 °C and 80% RH. Sets of columns were harvested after 1, 15, 29, and 91 days. In order to determine soil water retention curve, volumetric soil water content was measured using sample collected from the 6.35–11.4 cm depth at nine suction head. The analysis of the water retention curves was carried out using RETC (V6.02) model. Preliminary results showed that, generally there is a shift in soil pore size distribution in biochar treatments from Macro pores to Meso pores. A substantial reduction (on average 40%) happened in the most frequent pore size diameter in biochar treatments except for UTM 6%. The S-index which is the slope of the soil water retention curve at its inflection point and stands as a physical quality of soil increased in all soil mixtures with biochar. This analysis explores the mechanisms of the often observed increase in water holding capacity of sandy soils with biochar amendments.