Response of acidic silt loam soil properties to biochar application under soybean cultivation

Biochar is widely recognized for its potential to stabilize soil acidity and enhance carbon sequestration, yet its functional effects in temperate acidic silt loam soils remain insufficiently quantified. A two-year field study was conducted in Kentucky to evaluate changes in soil physicochemical properties following annual application of 12 t ha -1 of pine ( Pinus spp.) sawdust biochar (pyrolyzed at 650 °C) under continuous soybean ( Glycine max ) cultivation. Composite soil samples (0–15 cm) were collected pre-planting (May) and post-harvest (October) to monitor acidity indices, organic reserves, fertility indices, and hydrological properties. Biochar acted primarily as a chemical and carbonaceous stabilizer rather than an immediate fertility enhancer. The amendment significantly maintained higher post-harvest pH levels compared to the control, effectively buffering against the seasonal acidification observed in unamended plots. Soil organic carbon (SOC) and buffer pH exhibited a distinct “lag effect,” with significant increases emerging only after two years of cumulative application; at the final October 2024 sampling, SOC in the biochar-treated plots had increased to 1.96% from a 1.74% baseline, whereas the control plots declined to 1.66%. Conversely, soil fertility and hydrological parameters showed no significant treatment effects, being driven instead by seasonal environmental factors and crop uptake. These findings suggest that an annual application of 12 t ha − ¹ of pine biochar serves as an effective benchmark for mitigating acidification and building organic reserves in temperate silt loams, though further multi-rate studies are required to optimize application dosages for long-term agronomic use.