Fate of autumn-applied metolachlor in a clay loam in the northern U.S. Corn Belt.
Application of herbicides in autumn is of interest to land managers who seek to reduce the number of field operations during spring in the northern Corn Belt. A limited number of herbicides, however, posses the physical characteristics that are required to minimize loss from soil over winter. This study examined the fate of one of these herbicides, metolachlor, during three consecutive winters (1994-1995, 1995-1996, and 1996-1997) near Morris, MN. Metolachlor was applied to the top 5 cm of a clay loam that was packed into a 1.8-m long plastic pipe. The pipe was then set inside a larger diameter 1.8-m long plastic pipe that was buried vertically in the field. The gap between the pipes was insulated along the sides and sealed at the top; this configuration allowed collection of leachate and extraction of the smaller diameter pipe while the field soil was frozen. The experimental design was replicated thrice with sample date (date that the smaller diameter pipes were extracted from the field) as the main treatment. Pipes were extracted from the field at least twice during winter and sectioned into 2 cm or larger increments. The soil contained within these sections was then analyzed for metolachlor. Downward movement of metolachlor occurred in the soil profile during the autumn, but only in 1995. This movement was likely caused by exclusion during pore ice formation as the soil froze. At the time of complete soil thaw in spring, the majority of metolachlor was still detected in the zone of application (0-5 cm depth). Some metolachlor, however, was detected 1 to 3 cm below the zone of application in all three years. Downward movement during thaw was due primarily to infiltration of snowmelt and rain. Metolachlor was most vulnerable to degradation during spring, but some loss occurred in autumn prior to freeze-up. This study suggests that autumn-applied metolachlor moves little in a repacked clay loam profile during winter. Further studies are warranted in evaluating movement under a range of soil physical properties and management practices.
Sharratt
Brenton
B
USDA Agricultural Research Service, Morris, Minnesota 56267, USA. sharatt@morris.ars.usda.gov
Sander
Kip
K
Tierney
Dennis
D
D000081:Acetamides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D000327:Adsorption; D002980:Climate; D004784:Environmental Monitoring; D006540:Herbicides / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D012621:Seasons; D012989:Soil Pollutants / Q000032:analysis* / Q000378:metabolism; D014481:United States; D014872:Water Movements; D003313:Zea mays / Q000737:chemistry*
D000081:Acetamides; D006540:Herbicides; D012989:Soil Pollutants; C051786:metolachlor