Background: Though soils in the study areas are characterized by higher iron and aluminum oxides, and low available P contents, study on P adsorption characteristics is limited. The purpose of this experiment was to evaluate adsorption properties of selected soils and determine the standard phosphorous requirements of the soils. In this experiment, separately weighed 2 g soil samples were equilibrated in 50 ml of 0.01 M CaCl 2 solution containing KH 2 PO 4 at rates of 0, 1, 2.0, 4.0, 8.0, 16.0, 24.0, and 32.0 mg P L −1 .Results: The Freundlich model was found to be the best model for the description of the P adsorption characteristics of the soils. The Freundlich coefficient K f ranged from 123.32 to 315.31 mg P kg −1 . The Goha-1 soil had the highest K f (315.31 mg P kg −1 ) as Ketasire had lowest K f (123.32 mg P kg −1 ) values. The value of SPR f was ranged from 50.50 to 154.02 mg P kg −1 for soils of the study area. Highly significant (P ≤ 0.01) correlation was observed between the Freundlich adsorption parameters and soil physicochemical properties. Conclusion:The standard P requirement of the studied soils was higher than the blanket P fertilizer rate recommendations in Ethiopia. Lack of inadequate knowledge about internal and external P requirement of each crop might have decreased yield in the study areas as it could have resulted in under-application of fertilizer P. The presence of high correlation between the adsorption parameters and the soil properties suggested the indices' prominent role in explaining P adsorption characteristics of the soils. Since higher dose of P is required by soils in the study area because of fixation, alternative P management strategies is needed to reduce P adsorption and enhance P availability. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

Background: Soil acidity and low availability of P are among the major problems limiting crop production in the highlands of Ethiopia. The current study was conducted to evaluate the distribution of chemical P forms and selected physical and chemical properties of soils in Cheha and Dinsho districts, southern highlands of Ethiopia. Twelve representative composite soil samples were collected from the surface layer (0-15 cm) and analyzed for selected soil properties. Analysis of available P and oxalate extractable P, Al and Fe, and P fractionation were done following standard procedures. Results:The pH of soils in the study area ranged from 4.65 to 5.45. In the study area the Mehlich-3 extractable P ranged from 8.90 to 25.75 mg kg −1 , while the Bray-I extractable P varied from 8.54 to 22.81 mg kg −1. The studied soils had a total P content that ranged from medium to very high. Mehlich-3 P was positively and significantly correlated with pH, CEC and OM, while it was negatively and significantly (P ≤ 0.01) correlated with exAc and exAl. Oxyhydroxides of iron and aluminum were dominating the exchange sites of the studied soils. In terms of the relative abundance of P forms, Res-P and HCl-P followed by NaOH-P o and NaOH-P i were the dominant P forms in Cheha and Dinsho districts respectively. The total sum of readily available P forms (NH 4 Cl-P i , NaHCO 3 -P i and NaHCO 3 -P o ) did not exceed 4% of the total P. Conclusion:Soils of the study area were acidic in reaction and found to have low available P. Given the presence of considerable amount of total P, low P availability and high soil acidity in the study areas, further research has to be done on adsorption characteristics to determine the P requirements of the soils for better P management.