Faculty of Agricultural and Food Sciences

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Browsing Faculty of Agricultural and Food Sciences by Subject "Batch equilibrium experiment"

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    Phosphate and glyphosate sorption in soils following long-term phosphate applications
    (2017-12-01) Munira, Sirajum; Farenhorst, Annemieke; Akinremi, Wole
    Phosphate and glyphosate molecules compete for sorption sites in soil. The objective of this study was to quantify the impact of Olsen P concentrations in two contrasting soils on phosphate and glyphosate sorption. Soils were a sandy clay loam soil rich in iron oxides (SCL-Fe2O3) and a clay loam soil rich in calcium carbonates (CL-CaCO3). The phosphate Freundlich sorption coefficient (Kf) ranged from 3 to 68 L1/n mg1-1/n kg-1 in the SCL-Fe2O3 and from 21 to 76 L1/n mg1-1/n kg-1 in the CL-CaCO3. Glyphosate sorption coefficient (Kd) ranged from 293 to 1173 L kg-1 in the SCL-Fe2O3 but only 99 to 141 L kg-1 in the CL-CaCO3. Glyphosate Kd and phosphate Kf values decreased significantly with increasing Olsen P concentrations in both soils. Glyphosate Kd values were further significantly reduced when phosphate was added to the slurry solutions, but phosphate Kf values were not impacted by the presence of glyphosate in solutions. We conclude that annual phosphate fertilizer applications leave phosphate concentrations in Prairie soils to the extent that soils have a lesser capacity to retain glyphosate and phosphate that are subsequently applied, but glyphosate residues will not influence phosphate sorption.
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    Phosphate fertilizer impacts on glyphosate sorption by soil
    (Elsevier, 2016-05) Munira, Sirajum; Farenhorst, Annemieke; Flaten, Don; Grant, Cynthia
    This research examined the impact of field-aged phosphate and cadmium (Cd) concentrations, and fresh phosphate co-applications, on glyphosate sorption by soil. Soil samples were collected in 2013 from research plots that had received, from 2002 to 2009, annual applications of mono ammonium phosphate (MAP) at 20, 40 and 80 kg P ha-1 and from products containing 0.4, 70 or 210 mg Cd kg-1 as an impurity. A series of batch equilibrium experiments were carried out to quantify the glyphosate sorption distribution constant, Kd. Extractable Cd concentrations in soil had no significant effect on glyphosate sorption. Glyphosate Kd values significantly decreased with increasing Olsen-P concentrations in soil, regardless of the pH conditions studied. Experiments repeated with a commercially available glyphosate formulation showed statistically similar results as the experiments performed with analytical-grade glyphosate. Co-applications of MAP with glyphosate also reduced the available sorption sites to retain glyphosate, but less so when soils already contain large amounts of phosphate. Glyphosate Kd values in soils ranged from 173 to 939 L kg-1 under very strong to strongly acidic condition but the Kd was always < 100 L kg-1 under moderately acidic to slightly alkaline conditions. The highest Olsen-P concentrations in soil reduced Kd values by 25-44% relative to control soils suggesting that, under moderately acidic to slightly alkaline conditions, glyphosate may become mobile by water in soils with high phosphate levels. Otherwise, glyphosate residues in agricultural soils are more likely to be transported off-site by wind and water-eroded sediments than by leaching or runoff.