Submitted to: Journal of Environmental Science and Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/12/2002
Publication Date: 4/1/2003
Citation: SHARRATT, B.S., SANDER, K., TIERNEY, D. FATE OF AUTUMN-APPLIED METOLACHLOR IN A CLAY LOAM IN THE NORTHERN U.S. CORN BELT. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. 2003. v. B38(1). p. 37-48. Interpretive Summary: Fall application of herbicides is of interest to farmers who seek to reduce the number of field operations during spring in the northern Corn Belt. However, only a few herbicides possess the physical characteristics that are required to minimize loss from soil over winter. We monitored the movement of one such herbicide, metolachlor, in a soil during winter. Metolachlor did not move to any great extent within the soil during winter, but was susceptible to microbial degradation both in the autumn and spring. Metolachlor appears to be an environmentally safe herbicide that can be applied in the fall. Therefore, farmers can safely apply this herbicide in fall to control weeds the following spring in corn and soybean.
Technical Abstract: 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, possess 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 plastic pipe. The pipe was then set inside a larger diameter pipe that was buried vertically in the field. 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. 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.