Influence of monoammonium phosphate on glyphosate adsorption-desorption in tropical soils: Effect of the order of sorbate additions

• Published in: Chemosphere (Oxford) 2022-09, Vol.303 (Pt 1), p.135030, Article 135030
• Main Authors: Dotor-Robayo, Mónica Yadira, Guerrero-Dallos, Jairo Arturo, Martínez-Cordón, María José
• Format: Article
• Language: English
• Subjects: Adsorption; Adsorption isotherms; Glycine - analogs & derivatives; Glyphosate; Herbicides; Herbicides - analysis; Phosphate fertilizers; Phosphates; Soil; Soil Pollutants - analysis
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.135030

Glyphosate and phosphate compete for the same adsorption sites in the soil because their adsorption mechanisms are similar as the herbicide contains a phosphate group. However, how this competition occurs in relation to the order of addition of the sorbate and the composition of the soils remains unclear. The effect of the soil clay composition and the order of glyphosate and monoammonium phosphate (MAP) additions on glyphosate sorption-desorption was investigated using three inceptisols collected from Colombian rice fields. Glyphosate adsorption isotherms were evaluated using the batch equilibrium method and were modeled applying the Freundlich equation. The values for glyphosate Kfa, when evaluated alone, ranged from 14.39 to 639.86 mg1–na Lna kg−1. An agreement was found between adsorbed glyphosate, chlorites, and low initial phosphorous soil content. Preadsorbed MAP or simultaneous MAP-glyphosate additions to the soil revealed a drastic reduction in glyphosate Kfa values in soil containing the highest amount of 2 × 1 clays, but kaolinitic soils remained practically unaffected. Low desorption values could be associated with soils with the highest kaolinite content. Glyphosate remobilization was favored when the desorbing MAP solution was used in soils containing preadsorbed glyphosate. This study provides new knowledge on the effect of phosphorus fertilizers on glyphosate bioavailability in soils with different mineral compositions. [Display omitted] •Adsorption is correlated with soil chlorite content and low P levels in soils.•Preadsorbed MAP and co-applications with glyphosate can reduce glyphosate Kfa values.•Desorption percentages are inversely correlated with the soil kaolinite content.•Preadsorbed glyphosate is easily displaced by MAP additions.