Effect of Different Types of Biochar Amendment on Hydraulic Conductivity of Fine-Grained Soils
Abstract
Biochar has emerged as a promising sustainable soil amendment due to its potential to improve soil structure and enhance stormwater management. However, its effects on saturated hydraulic conductivity (Ksat) and unsaturated hydraulic conductivity (Kunsat) at high suction ranges (i.e., around 100 kPa) remain inconsistent due to variations in biochar properties. This study investigates the influence of nine commercially available wood-based biochars, applied at 3% and 6% rates, on two different fine-grained soils. Laboratory tests included determination of index properties, scanning electron microscopy (SEM), Ksat, and Kunsat of biochar soil mixtures. Ksat was measured using a falling head permeameter, and Kunsat was evaluated through evaporation tests. SEM analysis revealed varied surface structures and pore formations among the biochars, which indicate differences in feedstock characteristics. Results showed that biochar application, especially at 6% reduced bulk density, increased porosity, and improved Ksat and Kunsat in the biochar soil mixtures. Among the biochars tested, three types (Biochar Now Medium, Biochar Now Small, and Char Bliss) were most effective in increasing Ksat for both soils, while certain biochars (Blue Sky and The Anderson) exhibited limited or negligible effects. The primary influencing factors were soil type, biochar type, and application rate. Overall, these findings highlight the potential of biochar amendments to enhance soil infiltration and water retention, which offers practical benefits for managing stormwater runoff in fine-grained soils.