Changes in soil pH and addition of inorganic phosphate affect glyphosate adsorption in agricultural soil

Abstract

Glyphosate is the most widely used herbicide in Argentina. The strong sorption of glyphosate to the mineral fraction of the soil can be affected by environmental conditions and agricultural management, such as the application of fertilisers. This work aimed to study the effect of pH and the presence of inorganic phosphate on the affinity of glyphosate for nine different surface soils of Argentina. The effect of pH on glyphosate sorption was investigated by batch experiments with pH adjusted between 3 and 12. The greatest glyphosate adsorption occurred at a certain pH value and then adsorption decreased with increasing or decreasing pH. The effects of pH on adsorption could be described by a model that includes changes in electrical potential. The effect of inorganic phosphate on glyphosate adsorption was studied by batch experiments in the presence of 0.5 or 1 mM phosphate. The results showed a significant competition between phosphate and glyphosate in all soils. The Freundlich glyphosate coefficients decreased by 40%–65% with phosphate in solution, and the amount of glyphosate adsorbed decreased between 1% and 5%, depending on the particular characteristics of the soil. For the glyphosate‐phosphate competition, the competition terms were not reciprocal with each other because the competition between ions for adsorption sites also involves electrical effects. Highlights There is a pH at which glyphosate shows a higher affinity for the soil. The presence of phosphate significantly reduces the adsorption of glyphosate to the soil. The effects of pH can be explained by rather small changes in the estimated surface potential.

Loading Glyphosate in Attapulgite and Sodium Alginate Hydrogels to Construct pH-Responsive Controlled Release Microsphere for Enhanced Soil Sustained Release

“…The average Gly recoveries in soils ranged from 63 to 107%, and the data were corrected for blanks and surrogated recoveries. The method detection limits and instrumental detection limits of Gly were based on the previous method. , …”

“…The method detection limits and instrumental detection limits of Gly were based on the previous method. 6,35 2.7. Data Analysis.…”

“…Many environmental variables could significantly affect the activity of AI in Gly formulation, particularly, pH is reported as the determinant factor affecting Gly behavior in soils . With increasing soil pH, Gly becomes less active for its several acidity coefficients, and it is also pH-dependently absorbed in soils due to the different electrical charges of soil components and the Gly AI molecule . Thus, the spatial variations of soil pH would increase the losses of AI in Gly formulation, resulting in a repeated and indiscriminate application and consequently the increments in the cost and potential hazards to the nontarget organisms and ultimately human health .…”

“…4 With increasing soil pH, Gly becomes less active for its several acidity coefficients, 5 and it is also pH-dependently absorbed in soils due to the different electrical charges of soil components and the Gly AI molecule. 6 Thus, the spatial variations of soil pH would increase the losses of AI in Gly formulation, 4 resulting in a repeated and indiscriminate application and consequently the increments in the cost and potential hazards to the nontarget organisms and ultimately human health. 7 Therefore, it is significant to improve the Gly application efficiency and regulate its AI loss behavior in agricultural practices.…”

The Amino Acid Transporter PtCAT7 and Ammonium Nutrition Enhance the Uptake of Thiamethoxam in Citrus Rootstock Seedlings

“…However, the uptake of NH 4+ by plants increases hydrogen ion (H + ) release, resulting in lowing soil pH, and the lower pH affects the adsorption and degradation of pesticides in soil. 20,21 On the other hand, the application of pesticides influences the biochemical processes of nutrients. For instance, the application of pyrethrins and Neemix-4E reduced N leaching and increased the crop absorption rate.…”