Relationship Between Exchangeable Alumunium and Phosphorus Sorption Parameters of Indonesian Acid Soils

Abstract

In acid soils, phosphorus (P) sorption is generally attributed to hydrous oxides of Fe and Aluminum (AI) particularly in tropical soils with low pH. However, reports concerning the role of exchangeable AI in P sorption mechanism are very liltle. Phosphorus (P) sorption isotherms were studied in fifteen acid upland soils containing different amount of exchangeable AI. P sorption characteristics were satisfactorily described by the Langmuir equation. which was used to determine P sorption maxima and bonding energies, with r values ranging from 0.97 to 0.99. The soils varied widely in their capacities to sorb P. P sorption maxima rangedfrom 303 to 1429 mg kg-I (mean 627 mg kg-I) and bonding energies from 0.65 to 8.00 L mtl (mean 2.39 L mg-I). Exchangeable AI was found not correlated with P sorption maxima (r = -0.11) but significantly correlated with P bonding energies (r = 0.68**). This was clearly shown by clayey soils from Java and Sumatra but not in sandy soils from Kalimantan. The results suggested that in general. reaction of exchangeable AI with P increased P bonding energy but exchangeable AI was not the main component in P sorption maximum.