The effect of pH on phosphorus adsorption in acidic soils of Tsegede, western zone of Tigray, Ethiopia

Availability of phosphorous(P) is main challenges to crop production in the acid soils of the Tsegede. There is lack of information on which to base P fertilizer recommendations for production differences caused by acidity levels. This experiment was done in 2020 to evaluate Low phosphorus availability limits crop production in acidic soils of Tsegede due to strong P fixation. However, quantitative information on P adsorption characteristics across different acidity levels is lacking, hindering site-specific fertilizer recommendations. Adsorption characteristics and its relationship with soil properties were studied in acidic soils of Tsegede. KH2PO4 was used for the adsorption isotherm studies by duplicating 3 g from each soil types at different acidity ranges holding a total of ten soil samples with 50 ml of P in 0.01 M CaCl2, containing concentration of 0, 20, 40, 60, 80,100 mg L− 1. Langmuir and Freundlich adsorption isotherm models were used to describe adsorption processes. Results indicated that P adsorption increased significantly with the increase of P level and also P adsorption was increased as soil pH decline. Comparing the two models, the Langmuir linear model showed a better fit to the tested soils. The regression coefficients (R2) for the fitted Langmuir P adsorption isotherms were highly significant ranging from (0.955–0.999) for all tested soils except in moderate acidity in Dystric Cambisols. The adsorption maxima obtained from the Langmuir isotherm ranged from 357 mg P kg− 1 soil in strong acidic Dystric Cambisols to 2500 mg P kg− 1 soil in very strong acid Skeletic Leptosols. The bonding energy (k) for Langmuir adsorption model varied from 0.012 to 2.8 L mg− 1. Finally, increment of soil pH using amendment materials and their proper management in soils are important in making productive use and higher dose of P is required by soils because of fixation, alternative P management strategies is needed to reduce P adsorption and enhance P availability in such acidic soils in the study areas.