Soil acidity in Manipur's Entisols, Inceptisols, and Ultisols is mainly due to pH-dependent acidity. Hill soils have higher acidity than alluvial soils. Ammonium acetate extractable Al levels suggest the presence of soluble Al(OH)3 and hydroxy Al polymers. Exchange acidity is controlled by exchangeable Al3+, while pH-dependent acidity is influenced by organic matter and free iron oxides. Exchangeable Al3+ and aluminium saturation increase as soil pH decreases, reaching zero at pH 5.6. To manage acidic soils, liming is recommended to neutralize exchangeable Al3+ for better crop growth.