Properties of Soils Developed from Ultramafic Rocks and their Land Suitability for Cocoa in East Kolaka Regency, Indonesia

Abstract

Soils developed from ultramafic rocks are widely distributed in East Kolaka Regency, Southeast Sulawesi Province, Indonesia. However, the soil characteristics and their land suitability for cocoa crop have not been known. Three soil profiles developed from ultramafic rocks in East Kolaka were described, sampled, and analyzed to characterize their mineralogical, physical, and chemical properties. Results indicated that sand mineral composition was dominated by opaque, quartz, and garnet minerals, while clay minerals were composed of kaolinite, goetite and hematite. All the soils were characterized by clay textures, low bulk density (0.89-1.04 g/cm³), medium to very high available water (11-22%), and rapid permeability (13-25 cm/hour). The soil reaction was acid (pH 4.64-5.03). The soil organic carbon was medium in A horizon (2.02-2.95%) and very low in B horizons (0.35-0.87%). The N total values were medium to high in A horizon (0.37-0.51%) and low to very low in B horizons (0.07-0.18%). The available P and potential K₂O contents were very low, while the potential P₂O₅ content was low to medium (18-35 mg/100g).The exchangeable Ca content was low to very low (0.23-2.94 cmol_c/kg), while the exchangeable Mg content was low to high (0.22-2.59 cmol_c/kg). The soil CEC was low to very low (3-12 cmol_c/kg), while clay CEC was very low (< 6 cmol_c/kg). The base saturation was low to medium (19-51%), while Al saturation was very low (<3%). At family level, all the soils were classified as fine, kaolinitic, isohyperthermic, Rhodic Hapludox, All soils were marginally suitable (S3 class) for cocoa crop with limiting factors of acid soil reaction and very low potential K₂O. Liming and NPK fertilization should be applied to increase the soil productivity for cocoa development.

Keywords : soil properties, ultramafic rocks, land suitability, cocoa, East Kolaka