Medium term assessment of soil properties in a biochar amended Kentucky silty loam soil

Interest in biochar as a sustainable amendment is increasing, yet its medium-term effects on soil properties in fertile agricultural soils remain under-researched. Therefore, this study evaluated the effect of biochar treatment, soybean maturity group, and soil depth on selected physical and chemical properties of Kentucky silty loam soil. A field experiment was conducted using a split-split plot randomized complete block design with four replications, where the plot receiving the biochar and the untreated control plot were assigned as the main plot factor, soybean maturity groups were sub-plot factors, and soil depth was sub-sub plot factor. Biochar was applied at 12 t ha −1 yr − 1 over a two-year period, and soil samples were collected from two depths at the time of planting and after harvesting in the third year of study. At both sampling times, biochar treatment and soybean maturity groups showed no significant effects on most measured soil properties. However, biochar significantly increased the labile carbon permanganate oxidizable carbon (POXC) and manganese (Mn) after harvesting. POXC increased from 686.02 to 706.63 mg kg − 1, and manganese increased from 70.95 to 88.16 mg kg − 1 . Soil depth significantly influenced various soil properties. The surface layer (0–10 cm) had higher pore volume, organic matter, total carbon, total nitrogen, and micronutrient (Mn, Cu, B, and Zn), whereas the subsurface layer (10–20 cm) exhibited higher bulk density, cation exchange capacity, phosphorus, and calcium. Overall, biochar applications had limited effects on fertile, structurally stable silt loam soils over the medium term. Longer-term studies are needed to assess biochar’s role in maintaining soil fertility over time, and its potential as a preventive soil management strategy to sustain soil health before degradation occurs.