The Degradation and Bioactivity of Metolachlor in the Soil

Abstract

In bioassays, rice (Oryza sativaL.) recovery from metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] injury tended to be slower in flooded rice, but was not significantly different from the recovery rate in a nonflooded rice. In soils treated with 1 ppm (w/w) metolachlor and incubated in constant-temperature chambers, the half-life of metolachlor was shorter at 40 C than at 30 C. The degradation rate of metolachlor was not significantly correlated with declining moisture potentials in the range of −30 to −80 kPa. The CO2evolution from metolachlor-treated soil was negatively correlated with incubation time and positively correlated to declining moisture levels. In a field study, metolachlor, as determined by bioassay, was mobile in a Taloka silt loam soil profile. After being incorporated to 7.5 cm, it became evenly distributed in the top 15 cm of the soil profile within 18 days. Metolachlor adsorption was positively correlated with clay and organic carbon content.

Degradation and Persistence of Metolachlor in Soil: Effects of Concentration, Soil Moisture, Soil Depth, and Sterilization

“…Merr. Biodegradation is the primary means of metolachlor dissipation in soil [11][12][13][14]. Large quantities of metolachlor (22 million kg of active ingredient) are applied to agricultural fields in the United States, particularly in the Midwest, where most of the nation's corn and soybeans are grown [6,10].…”

Metolachlor persistence in laboratory and field soils under Indian tropical conditions

“…Persistence of metolachlor in the field varies widely depending on temperature, sou •type, sou water and depth below the sou surface (Walker and Zimdahl, 1981;Braverman et al, 1986;Bowman, 1990;Nilsson 1991;Buttle and Harris, 1991;Burgard et al, 1993;Keller and Weber 1995;Zheng and Cooper 1996). Fifty percent dissipation times (DT 50 ) in field studies have ranged from 24 to 108 days (Frank et al 1991;Burgard et al 1993;Zheng and Cooper 1996;Aga et al, 1996) and carry over of significant metolachlor residues into the next cropping year has been observed in various soils (Braverman et al, 1986, Wood et al, 1987, Huang and Frink 1989, Sauer et al 1990Burgardetal., 1993).…”

“…Fifty percent dissipation times (DT 50 ) in field studies have ranged from 24 to 108 days (Frank et al 1991;Burgard et al 1993;Zheng and Cooper 1996;Aga et al, 1996) and carry over of significant metolachlor residues into the next cropping year has been observed in various soils (Braverman et al, 1986, Wood et al, 1987, Huang and Frink 1989, Sauer et al 1990Burgardetal., 1993). However, not much information is available on the persistence of metolachlor in tropical soil except a green house study conducted by Sahid and Wei (1993) under Malaysian conditions and no report is known to exist on field persistence of this herbicide.…”

Fate of metolachlor under subirrigation in a sandy soil: A lysimeter study

“…Metolachlor is reported to be a mobile herbicide with high leaching capabilities (Braverman et al, 1986). Obrigawitch et al (1981) adsorption and high mobility of metolachlor in clay loam and sandy loam soils containing less than 1% organic matter.…”

“…This laboratory finding confirms the lysimeter study's results: metolachlor residues in soils of subirrigated corn and soybean farms in Quebec may not reduce significantly. Braverman et al (1986) also found that metolachlor degradation was not significantly correlated to soil moisture levels in a silty loam soil at 30 and 40 °C. These findings imply that other BMPs must be explored to examine the possibility of reducing environmental pollution from agricultural farms which use the herbicide metolachlor.…”