Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/29/2005
Publication Date: 5/18/2005
Citation: Accinelli, C., Koskinen, W.C., Seebinger, J.D., Vicari, A., Sadowsky, M.J. 2005. Effects of incorporated corn residues on glyphosate mineralization and sorption in soil. Journal of Agricultural and Food Chemistry. 53:4110-4117. Interpretive Summary: In modern agricultural systems employing conservation tillage system, glyphosate is widely used as a burndown herbicide in a wide range of crops. Considering that conservation tillage systems can have considerable amounts of crop residues on the soil surface, glyphosate may bind to the decomposing crop residues, which in turn affects its availability to dissipate, possibly increasing its persistence in the environment. The objective of this research was to determine the influence of incorporation of varying amounts of corn residues in soil on glyphosate dissipation. We found that incorporation of corn residues in soil, at amounts normally found under conservation tillage systems, did not have a significant affect on glyphosate degradation in sandy and sandy loam soils. It appears that farmers can continue to safely use glyphosate as a burndown treatment in crops under conservation tillage systems, as crop residues do not increase glyphosate persistence in the environment.
Technical Abstract: In modern agricultural systems employing conservation tillage practices, glyphosate is widely used as a burndown herbicide in pre-planting of a wide range of crops. Considering that conservation tillage systems are characterized by a significant presence of crop residues at the soil surface, applied glyphosate is expected to encounter a soil matrix rich in poorly decomposed crop residues. In the present study, the influence of incorporation of different ratios of corn residues on mineralization and sorption of 14C-glyphosate was determined. Investigations were conducted under laboratory conditions using sandy loam and sandy soil samples and powered corn residues obtained from two corn hybrids: a stacked trait hybrid (Bt-protected and glufosinate-tolerant hybrid), and the corresponding non-transgenic isoline. Incorporation of corn residue in the range from 0.5 to 4% caused different effects on mineralization and sorption of 14C-glyphosate in the two soils. More specifically, low levels of incorporated corn residue did not affect or slightly stimulated herbicide mineralization in the sandy and sandy loam soils, respectively. In the sandy soil, incorporation of the highest level of corn residues (4%) caused a significant decrease in 14C-glyphosate mineralization. 14C-glyphosate sorption on both soil types was significantly reduced in samples receiving high amounts of incorporated corn residues. Regardless of the added level, corn residues from the two isolines showed similar behavior in their effects on both mineralization and sorption of 14C-glyphosate in the sandy loam and in sandy soils.