Potassium distribution of a toposequence provides management information for landscape sustainability. Potassium forms (total, structural, Fixed, Available, Exchangeable and Solution) in bulk and particle size fractions of soils on a toposequence in Mbano, Southeastern Nigeria were studied. Total, structural, fixed, available, exchangeable and solution K in bulk soil, sand, silt and clay particle size fractions ranged between 0.44-0.88, 0.21-0.59, 0.09-0.22, 0.13-0.33, 0.09-0.22 and 0.04-0.11 and 0.45-0.73, 0.05-0.27, 0.06-0.20, 0.11-0.26, 0.07-0.17 and 0.04-0.08 cmol+ kg-1 in A and AB horizons respectively. Also, concentration of most K forms in bulk soil and particle size fractions decreased in the order total > structural > available > fixed > exchangeable > solution for both horizons. Equally, within each horizon K forms varied with physiographic positions (summit, mid-slope and toe-slope) with concentrations of bulk soil, sand and clay particle size fractions better in the summit and that of the silt size fraction in the toe-slope of the A horizon while those of bulk soil and all particle fractions size fractions better in the toe-slope of the AB horizon. Furthermore, in each physiographic position, K enrichment of soil particle size fractions for A and AB horizons decreased in the order clay > silt > sand. Bulk soil and particle size K fractions correlated (P < 0.05) with soil ECEC, pH, OM, P, total N, sand, silt, clay and silt/clay ratio. In, general distribution of K forms in particle size fractions along a toposequence suggests the need for consideration of active soil portions for sustainable K management of the environment.
Keywords: Mbano and Southeastern Nigeria, Particle Size, Potassium Forms, Toposequence
