Phosphorus sorption by Andepts from the Southern Highlands of Papua New Guinea

Abstract

P sorption curves (18 hours, 0.01 M CaCl 2) were determined for various A, AB, B and C horizons of six Andepts. Two of these soils were formed in alluvially sorted and redeposited volcanic ash. P buffer capacity (PBC) and equilibrium solution P concentration (EPC) were derived from the curves. PBC was high for all samples indicating large sorption capacities. Soils formed in alluvial ash had lower PBC than those developed in airfall ash. In the latter soils, PBC was affected by degree of weathering. Multiple regression indicated that most variation in PBC was accounted for by citrate-dithionite minus pyrophosphate extractable Al, oxalate minus pyrophosphate extractable Al, and pyrophosphate extractable Fe. This suggests that allophane, crystalline and non-crystalline aluminium hydrous oxides, and Fe associated with organic matter, account for the predominant P-sorbing sites. The low EPC figures, which were correlated with Olsen extractable P, indicate potential P deficiency as a limitation to crop production.