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ARS Home » Southeast Area » Stoneville, Mississippi » Crop Production Systems Research » Research » Publications at this Location » Publication #236286
Title: Soil Depth and Tillage Effects on Glyphosate Degradation

Author
item ZABLOTOWICZ, ROBERT
item ACCINELLI, CESARE - UNIV OF BOLOGNA
item KRUTZ, LARRY
item Reddy, Krishna

Submitted to: Journal of Agriculture and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/17/2009
Publication Date: 6/3/2009
Citation: Zablotowicz, R.M., Accinelli, C., Krutz, L.J., Reddy, K.N. 2009. Soil Depth and Tillage Effects on Glyphosate Degradation. Journal of Agriculture and Food Chemistry 57:4867-4871.

Interpretive Summary: The use of glyphosate-resistant crops facilitated the widespread adoption of no-tillage (NT) cropping systems. Theobjectives of this study was to determine glyphosate sorption, mineralization, and persistence at two depths [0- to 1 inch (A) and 1-4 inches (B)] in a silt loam managed under long term conventional-tillage (CT) or NT soybean. Relative to the other soils, organic carbon (OC) and fluorescein diacetate (FDA) hydrolytic activity were at least 1.4-fold higher in NT-A. Glyphosate sorption was greatest in the lower depth of NT soil and was not correlated with OC. Cumulative glyphosate mineralized after 35 d was highest in NT-A soil, intermediate in CT-A and CT-B, and least in NT-B. Mineralization was positively correlated with OC and FDA activity, but negatively correlated with sorption indicating that sorption decreased bioavailability. Independent of tillage and depth, the half-life for extractable residues was less than 14.2 d. These data indicate that glyphosate sorption and persistence is similar between the surface of NT and CT soils, and that the adoption of NT will likely have minimal impact on the risk for glyphosate leaching or transport in surface runoff.

Technical Abstract: The use of glyphosate-resistant crops facilitated the widespread adoption of no-tillage (NT) cropping systems. The experimental objectives were to determine glyphosate sorption, mineralization, and persistence at two depths [0- to 2- cm (A) and 2- to 10-cm (B)] in a silt loam managed under long term conventional-tillage (CT) or NT soybean. Relative to the other soils, organic carbon (OC) and fluorescein diacetate (FDA) hydrolytic activity were at least 1.4-fold higher in NT-A. Glyphosate Kd values ranged from 78.2 to 48.1 and were not correlated with OC. Cumulative glyphosate mineralized after 35 d was highest in NT-A soil (70%), intermediate in CT-A and CT-B (63%), and least in NT-B (51%). Mineralization was positively correlated with OC and FDA activity, but negatively correlated with Kd indicating that sorption decreased bioavailability. Independent of tillage and depth, the half-life for 0.01 N CaCl2 and 0.1 N extractable residues (bioavailable residues and residues bound to Fe and Al oxides, respectively) was =1.2 h and =14.2 d, respectively. These data indicate that glyphosate sorption and persistence is similar between the surface of NT and CT soils, and that the adoption of NT will likely have minimal impact on the risk for glyphosate leaching or transport in surface runoff.