Soil Cover and Tillage Influenced Metolachlor Mobility and Dissipation in Field Lysimeters

Abstract

Leaching studies using soil column field lysimeters were conducted in 1991 and 1992 to determine the influence of tillage [conventional (CT) and reduced (RT)], soil cover (fallow, soybean, and bermudagrass sod), and water input level on 14C metolachlor mobility. Runoff and leachate collectors were installed. Leachate was collected weekly and analyzed for herbicide content. At 128 d after treatment (DAT), the lysimeters were removed, and the soil was analyzed for herbicide concentration as a function of depth. In 1991, 10% greater amounts of 14C metolachlor volatilized from CT than from RT (32 vs. 22%). Amounts of metolachlor recovered in surface cover were 2.3% less (2.1 vs. 4.4%), amounts in subsoil were 8% less (47 vs. 55%), and amounts recovered in leachate were 0.7% less (0.7 vs. 1.4%) under CT than RT. In 1992, measured parameters of 14C distribution in soil for tillage treatments were similar, except 14C recovered in leachate was 3% greater under RT (7 vs. 4%). Amounts of 14C metolachlor retained by soil cover were greatest in bermudagrass sod (16%), less in soybean (4%), and least in fallow (1%) and were similar for each treatment both years. Carbon‐14 metolachlor recovered in leachate of all treatments was approximately five times greater in 1992 (5%) than in 1991 (1%) due to the 7% greater water input in 1992, much of which occurred shortly after Day 0. Leachate volume collected in 1992 (8 L) was also twice that of 1991 (4 L). Tillage and soil cover interaction effects occurred both years.

Tillage management effects on pesticide fate in soils. A review

“…VII). Although most of these works showed greater losses under conservation tillage Isensee et al, 1990;Masse et al, 1998;Singh et al, 2002;Weber et al, 2006), results are contrasted, some of them indicating no effect of tillage (Clay et al, 1998;Fomsgaard et al, 2003;Gaynor et al, 2000;Granovsky et al, 1993;Weed et al, 1995), or even greater losses under conventional tillage (Düring and Hummel, 1993;Gish et al, 1995;Levanon et al, 1993).…”

“…Volatilisation directly depends on environmental conditions and is favoured first by high temperatures (Glotfelty, 1987;Weber et al, 2002) and also by wet soils that keep the molecules available in water solution. Weber et al (2006) observed during a year of monitoring that volatilisation reached 22 and 32% of applied metolachlor in conservation tillage and conventional tillage, respectively. Due to the mulch, soil surface water content was higher under conservation tillage, which slowed down the soil warming and thus reduced the amount of herbicide lost.…”

Leaching of the S-metolachlor herbicide associated with paraquat or glyphosate in a no-tillage system

“…The atrazine herbicide shows less leaching in a no-tillage system, when compared to conventional tillage (Weber et al 2006b), likely due to the fact that the plant cover exhibits greater sorption capacity than the soil.…”

Effect of rainfall regimes and mulch decomposition on the dissipation and leaching of S -metolachlor and glyphosate: a soil column experiment

“…Losses due to leaching are considered to be more important in these systems because of greater water infiltration and development of macropores, which can induce preferential flow. Greater leaching losses of metolachlor, atrazine and other herbicides were reported, which were attributed to the development and preservation of macropores formed by roots and earthworm burrows under no‐tillage practices . Meanwhile, reduced leaching of insecticides and many herbicides was also reported and was attributable to their greater retention in surface soil owing to increased organic matter content .…”