article · ENVIRONMENTAL SYSTEMS RESEARCH
Soils in the Cheha and Dinsho districts of southern Ethiopia contain high levels of iron and aluminium oxides, leading to low available phosphorus. An evaluation of phosphorus adsorption across these acidic soils revealed that the Freundlich model accurately described their behaviour. Adsorption capacity varied substantially among local soil types, with the Freundlich coefficient ranging from 123.32 to 315.31 milligrams of phosphorus per kilogram. The standard phosphorus requirements of the tested soils spanned from 50.50 to 154.02 milligrams per kilogram. These requirements significantly exceeded Ethiopia's standard blanket fertiliser recommendations, suggesting that existing practices lead to phosphorus under-application and potential crop yield reductions. Furthermore, strong correlations linked phosphorus adsorption parameters directly to underlying soil physicochemical traits. Because these soils fix significant amounts of phosphorus, alternative soil management approaches are needed to minimise adsorption and improve nutrient availability for agriculture.
Acidic soils rich in iron and aluminium bind phosphorus tightly, making the essential nutrient unavailable to crops. Applying fertiliser based on generic regional recommendations risks under-fertilising these soils, capping agricultural productivity. Understanding local adsorption rates allows agronomists and policymakers to revise nutrient guidelines, ultimately helping farmers address nutrient fixation and improve crop yields across affected highland regions.
This early-stage research provides baseline soil chemistry data that could inform regional fertiliser blending companies, agricultural extension services, and soil testing laboratories. The findings highlight that standard fertiliser doses are insufficient due to high fixation, pointing toward the need for tailored fertiliser formulations or soil amendments. Commercial implementation remains at an applied research stage, requiring field-level testing to translate these laboratory adsorption metrics into specific, cost-effective product recommendations.
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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 CaCl2 solution containing KH2PO4 at rates of 0, 1, 2.0, 4.0, 8.0, 16.0, 24.0, and 32.0 mg P L−1. The Freundlich model was found to be the best model for the description of the P adsorption characteristics of the soils. The Freundlich coefficient Kf ranged from 123.32 to 315.31 mg P kg−1. The Goha-1 soil had the highest Kf (315.31 mg P kg−1) as Ketasire had lowest Kf (123.32 mg P kg−1) values. The value of SPRf 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. 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.
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DOI: 10.1186/s40068-018-0121-1
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