Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/1995
Publication Date: N/A
Citation: Interpretive Summary: Every spring herbicides are applied to millions of acres of cropland in the United states. At Coshocton, Ohio, the USDA Agricultural Research Service has a 1000-acre watershed research station where we can measure how such herbicides persist and move in our environment. Last year, we sprayed two commonly used herbicides (atrazine and alachlor) in three corn fields; one that was plowed, one no-till with cattle manure, and another no-till without manure. In all three fields, we used a portable rainfall simulator to create surface puddles which were sampled to define their herbicide content 1, 2, 4, 8, 16, and 32 days after the spray had been applied. On every sampling day, we rained in a new place in each field with a storm that lasted for 30 minutes. Herbicide concentrations in the surface water decreased rapidly during each 30-minute rain and also over the 32-day study. Five minutes after the puddles first formed concentrations were only about 2/3 of the initial concentrations, and by 30 minutes, they had decreased another third. One month after spraying, the highest herbicide concentrations were about one tenth of those on day 1. This study supports earlier conclusions that if much herbicide moves in either surface runoff or in water that infiltrates into the soil, it will happen only in the first few storms that occur shortly after the chemicals have been applied.
Technical Abstract: The annual springtime application of herbicides for weed control in corn fields is a potential source for pollution of both surface and ground water. Although herbicide concentrations in runoff water from treated fields usually decrease with time, reports of maximum in-field concentrations soon after application are lacking. To characterize this potential contribution to ground water contamination, we treated one plowed and two no-till corn fields with 2.24 and 3.36 kg/ha, respectively, of atrazine and alachlor. We used a simulator to rain on plots within the fields 1, 2, 4, 8, 16, and 32 days after herbicide application and collected water that accumulated in surface depressions 0, 5, 10, 15, 20, and 30 min after initial ponding. Highest atrazine concentrations were found in t = 0 samples on day 1, ranging up to 2 mg/L in the no-till and 10 mg/L in the plowed areas. At t = 5 and t = 30 min, atrazine concentrations averaged 2/3 and 1/4 of the t = 0 values, respectively. Alachlor concentrations were 1/2 to 1/3 of atrazine values in the same samples. By day 32 initial concentrations of both herbicides were about 10 % of those on day 1 and continued to decrease during the 30-min sampling period.