Phosphate fertilizer impacts on glyphosate sorption by soil

Area of Science:

• Environmental Chemistry
• Soil Science
• Agrochemicals

Background:

• Long-term agricultural practices involve applying phosphate fertilizers and can introduce impurities like cadmium (Cd).
• Understanding how these soil amendments affect pesticide behavior is crucial for environmental risk assessment.
• Glyphosate sorption is a key factor determining its fate and transport in soils.

Purpose of the Study:

• To investigate the influence of aged phosphate and cadmium concentrations, and fresh phosphate co-applications, on glyphosate sorption in soil.
• To quantify the glyphosate sorption distribution constant (Kd) under various soil conditions.
• To assess the impact of soil properties on glyphosate mobility.

Main Methods:

• Soil samples from long-term experimental plots with known phosphate and cadmium treatments were analyzed.
• Batch equilibrium experiments were conducted to determine the glyphosate sorption distribution constant (Kd).
• The effects of varying Olsen-P and extractable Cd concentrations, as well as pH, on glyphosate sorption were evaluated.

Main Results:

• Extractable soil cadmium concentrations did not significantly affect glyphosate sorption.
• Glyphosate Kd values decreased significantly with increasing soil Olsen-P concentrations across different pH levels.
• Co-application of monoammonium phosphate (MAP) with glyphosate reduced sorption sites, but less so in high-phosphate soils.
• Glyphosate Kd was significantly lower in moderately acidic to slightly alkaline soils compared to acidic conditions.

Conclusions:

• High soil phosphate levels, particularly in moderately acidic to alkaline soils, can significantly reduce glyphosate sorption, potentially increasing its mobility.
• While cadmium did not impact sorption, elevated phosphate levels suggest a greater risk of glyphosate transport via water under specific soil conditions.
• Glyphosate residues are more likely to be transported by wind and erosion than by leaching or runoff in most tested agricultural soils, except under high phosphate conditions.