Study on mechanism of biochar improving acid Soil: Multi-scale experiment and numerical simulation

This study explored peanut shell biochar's remediation effects on acidic soils through leaching experiments and numerical simulations. Five biochar application rates (0-10 %) were tested under leaching (LP) and natural (NP) conditions. Biochar significantly increased soil pH (from 5.23 to 6.81 in 10 cm LP soil at 10 % treatment) while reducing electrical conductivity (173.6 μS/cm) and exchangeable acid (0.15 μmol/kg). Leaching accelerated pH improvement, with acidic ion migration reaching 15.87 %. Biochar's alkaline components (carbonates/ash) neutralized acidity, while surface functional groups adsorbed acidic ions. Its porous structure retained base ions and enhanced macro-aggregate formation (>0.25 mm, +35 %), improving water retention. Numerical simulations revealed increased porosity (58.03 % at 10 % treatment) and reduced outflow rate (-64.5 %) through flow impedance and low-velocity zone formation. The dual mechanism combines chemical neutralization, physical adsorption, and hydrodynamic modification, demonstrating biochar's synergistic potential for acidic soil remediation. These findings provide theoretical support for sustainable agricultural practices using organic amendments.