title: Reduced surface runoff losses of metolachlor in narrow-row compared to wide-row soybean.
abstract: Cultural management practices that reduce the off-site transport of herbicides applied to row crops are needed to protect surface water quality. A soybean [Glycine max (L.) Merr.] field study was conducted near Stoneville, MS on Sharkey clay to evaluate row spacing (50 cm vs. 100 cm) effects on metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methoxy-1-methylethyl) acetamide] transport. One day after the foliar application of metolachlor to 2.03 m wide by 2.43 m long plots, 60 mm h(-1) of simulated rainfall was applied until 25 min of runoff was generated per plot. The calculated mass of metolachlor intercepted by the soybean foliage was greater in narrow-row than wide-row soybean, 0.39 kg ha(-1) vs. 0.23 kg ha(-1), respectively. Field and laboratory studies indicated that less than 2% of the metolachlor intercepted by the soybean foliage was available for foliar wash-off 1 d after application. Antecedent soil water content at the start of the simulations was lower in narrow-row soybean. In turn, there was a 1.7-fold greater time to runoff on narrow-row plots. The greater time to runoff likely contributed to lower metolachlor concentration in runoff from narrow-row plots. Cumulative metolachlor losses were significantly greater in wide-row than narrow-row soybean, 3.7% vs. 2.2%, respectively. Findings indicate that narrow-row planting systems may reduce metolachlor runoff following a post-emergence application.
authors.affiliation: USDA-ARS, Southern Weed Science Research Unit, P.O. Box 350, Stoneville, MS 38776, USA. Jason.krutz@arz.usda.gov
authors.forename: L Jason
authors.initials: LJ
authors.lastname: Krutz
authors.forename: Clifford H
authors.initials: CH
authors.lastname: Koger
authors.forename: Martin A
authors.initials: MA
authors.lastname: Locke
authors.forename: Robert W
authors.initials: RW
authors.lastname: Steinriede
mesh_terms: D000042:Absorption; D000081:Acetamides / Q000032:analysis*; D004784:Environmental Monitoring; D006540:Herbicides / Q000032:analysis*; D011891:Rain; D012987:Soil; D012989:Soil Pollutants / Q000032:analysis; D013025:Glycine max / Q000254:growth & development*; D013997:Time Factors; D014877:Water Pollution, Chemical / Q000517:prevention & control*
chemical_list: D000081:Acetamides; D006540:Herbicides; D012987:Soil; D012989:Soil Pollutants; C051786:metolachlor