Department of Plant Sciences

Glyphosate, a broad spectrum, non-selective herbicide, is the world´s most important and widely used herbicide. The globally increasing adoption of no-till or reduced tillage systems is becoming a driving force for enhanced glyphosate use. In such systems, glyphosate is applied pre-sowing for weed control and glyphosate may remain in root and shoot residues. To evaluate potential risks associated with glyphosate residues, a pot experiment was conducted under controlled greenhouse conditions with two contrasting soils: weakly buffered acidic Arenosol and highly buffered Luvisol. Glyphosate was supplied as glyphosate enriched rye grass straw (1.2 g DM kg-1 soil) prior to sowing sunflower as a non-target plant. Several physiological parameters, such as intracellular shikimate accumulation as a metabolic indicator for glyphosate toxicity, biomass production and micronutrient status were analyzed. Detrimental effects on sunflower plants linked to glyphosate toxicity were observed only in the Arenosol but not in the Luvisol. This is most probably related to the difference in soil properties. The detoxification capacity of the fine-textured Luvisol, with a high clay content, was high enough for an adequate immobilization and inactivation of glyphosate. On the sandy Arenosol, the level of glyphosate supply exceeded the detoxification capacity. In addition to the difference in detoxification capacity, differences in nutrient bio-availability might also have aggravated the observed inhibition of nutrient acquisition. Thus, the findings suggest the importance of weed residues in transferring glyphosate from target to non-target plants, particularly in no-till or reduced tillage systems, with the consequence of detrimental effects on following crop plants.