Phosphorous Sorption Characteristics of Soils in Smallholding Land Use in Southern Ethiopia

Purpose. This study evaluated the P sorption characteristics of soils under smallholding land use in Wolaita Zone, Southern Ethiopia. Methods. Soil samples (0–20 cm) were collected from each of the home garden, grazing land, cropland, and woodlot in three replications at two sites and analyzed for P sorption isotherm data and selected soil properties. Results. The P sorption data were generated by equilibration with P solutions and the data were fitted with the Freundlich model (r2 = 0.88–0.98, SE = 0.16–0.24) and Langmuir model (r2 = 0.81–0.98, SE = 0.45–1.71). The Langmuir P sorption maximum (Qmax) and Freundlich sorption coefficient (Kf) were the highest in the cropland soils while these parameters were the lowest in the home garden. Maximum buffering capacity (MBC) was in the order cropland > woodlot > home garden > grazing land, but Freundlich P buffering capacity (PBC) followed the order cropland > grazing land > home garden > woodlot. Langmuir bonding energy (bL) and Freundlich phosphate sorption affinity (1/n) were in the order of home garden > woodlot > grazing land > cropland. The Qmax was positively correlated (p < 0.05) with clay, Kf, PBC, the oxalate and dithionates extractable Al, Fe, and Mn, but it negatively correlated (p < 0.05) with soil pH, SOC, AP and bL. Conclusion. Generally, the effect of P sorption of the smallholding home garden was slightly different from eucalyptus woodlot and grazing lands but considerably different from cropland. The high P sorption capacity in cropland was attributed to the high amorphous and crystalline Fe/Al oxides/hydroxides, low SOC, and low soil pH. Hence, combinations of P managements are required for increasing P availability in the smallholding land uses.