Surface application of liming materials with biochar and organic amendments for subsoil acidity amelioration in the laterite soils

The study aimed to evaluate liming materials combined with biochar and organic amendments for surface and subsoil acidity amelioration. A soil column incubation study was conducted under laboratory conditions for 12 weeks using the southern laterite soils (AEU-8) of Kerala, at College of Agriculture, Vellayani. The 17 treatments studied included farmyard manure (FYM) at 20 t ha− 1, humic acid (HA) at 10 kg ha− 1, poultry manure (PM) at 1 t ha− 1 and coconut frond biochar (CFB) at 10 t ha− 1 each in combination with lime, dolomite, calcium silicate (CS) or phosphogypsum (PG) at lime requirement (LR) and a soil alone control. After 12 weeks of incubation, soil pH was highest under CFB at 10 t ha⁻¹ with lime as per LR (6.7 at 0–15 cm), FYM at 20 t ha⁻¹ with CS as per LR (5.8 at 15–30 cm), and CFB at 10 t ha⁻¹ with PG as per LR (5.16 at 30–60 cm). Application of CFB at 10 t ha⁻¹ with CS as per LR significantly lowered exchangeable Al³⁺ (0.16, 0.16, 0.42 meq 100 g⁻¹) and H⁺ (0.11, 0.13, 0.21 meq 100 g⁻¹) while enhancing Ca²⁺ (792.46, 521.68, 498.69 meq 100 g⁻¹), and CFB at 10 t ha⁻¹ with dolomite as per LR maintained higher Mg²⁺ values (103.60, 90.31, 89.05 meq 100 g⁻¹) across soil depths. Among the tested combinations, the application of CFB at 10 t ha− 1 with CS ad per LR most effectively ameliorated subsoil acidity, followed by the treatment CFB at 10 t ha-1 with dolomite as per LR.