Testing of applicability and flexibility of isotherm equations to fit sulphate kinetics desorption data in Nigerian savanna soils

Abstract

Most agricultural soils exhibit minimal recovery of sulfate (S), the accuracy of isotherms to describe anion desor-ption data is very useful in establishing the fertilization schedule to promote optimal crop yield. The desorption of S by savanna soils and its applicability to isotherm equations in reserve form are both poorly understood. To fill this gap, soil samples were collected from three distinct parent materials: Basement Complex Rock, Chad Formation Rock, and Kerri-Kerri Formation Rock. Experimental soils were mixed with a 15 ml solution of Cal-cium dihydrogen phosphate containing 500 mg P/l for sulfate desorption analysis. Mixed samples were then shaken for different durations (30, 60, 150, 180, and 240 minutes). The data indicate a significant va-riation in soil pH among different parent materials. The isotherm equations were successfully applied to the de-sorption data of sulfur, with R2 values exceeding 0.98 for both Langmuir and Freundlich equations. The Langmuir equation proved to be the most suitable for the desorption data, as evidenced by low standard error. The order of desorption and fitness was found to be CFR > BCR > KKFR. Langmuir desorption qmax and KL were found to be favorably and significantly associated with pH, ​​Org C, and Alox. A negative and statistically significant relationship between Alox and Freundlich desorption nF was observed. The results showed that different mechanisms contribute to sulfate desorption from soils. To use fertilizers in the soil more efficiently, it is necessary to consider contact time, add forms of oxides as a filler to the S-formulated fertilizer, and apply organic management methods to support sustainable agriculture in the studied area.

Keywords

• testing
• applicability
• isotherm equations
• desorption
• sulphate