Reduced surface runoff losses of metolachlor in narrow-row compared to wide-row soybean

Cultural management practices that reduce the off-site transport of herbicides applied to row crops are needed to protect surface water quality. 4 soybean [Glycine max (L.) Merr.]field study was conducted near Stoneville, MS on Sharkey clay to evaluate row sparing (50 cm vs. 100 cm) effects' on metolachlor [2-chloro-N-(2-ethyl-6-metfiylphenyl)-N-(methoxy-1-methylethlyl) acetamide] transport. One day after, the foliar application of metolachlor to 2.03 m wide by 2.43m 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, 1 metolachlor runoff following a post-emergence application.