Skip to main content
ARS Home » Research » Publications at this Location » Publication #69858
Title: AFFECT OF CONTROLLED WATER TABLE ON RUNOFF LOSSES OF SOIL-APPLIED CHEMICALS

Author
item Southwick Jr, Lloyd
item Willis, Guye
item Fouss, James
item Carter, Cade

Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/26/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Runoff losses of atrazine, metolachlor, pendimethalin, and chlorpyrifos were measured from plots laid out on a MS River alluvial soil. The two years of data reported here comprise part of a study on the utility of controlling water tables by subsurface drainage-subirrigation for the reduction of runoff and leaching losses of agrichemicals. The present report is limited to those plots without subsurface drainage. Initial concentrations of these chemicals in runoff reflected the differences in their water solubilities. Atrazine and metolachlor showed initial concentrations in runoff of 60-150 ppb. Pendimethalin and chlorpyrifos exhibited early concentrations in runoff of 0.6-2.5 ppb. Total losses in runoff over the 5-6 month periods of the study amounted to 1.1-3.5% of the applications for atrazine and metolachlor and to 0.004-0.13% of the applications for pendimethalin and chlorpyrifos. Subsurface drainage is known to effectively reduce water and sediment loss in runoff from agricultural fields. In addition, subsurface drainage in conjunction with subirrigation has the theoretical potential of keeping chemicals in soil leachate in the root zone where they can exert their effects longer and undergo soil-mediated degradation processes, rather than leaching past this zone.

Technical Abstract: Atrazine, metolachlor, chlorpyrifos, and pendimethalin were applied on May 25, 1994 without incorporation to sixteen 0.2 ha plots of Commerce silty clay loam planted to corn. Concentrations of these chemicals in runoff over the next 193 days decreased at rates similar to those of the concentrations of the chemicals in the top 2.5-cm soil layer. DT50s of the chemicals in soil were about 15 days; DT90s were 50-60 days. Concentrations of these pesticides in runoff decreased by 50% by day 20 and reached 10% of their initial values around day 50. Initial concentrations in runoff reflected the differences in water solubilities (S) of these pesticides: atrazine (S = 33 mg/L) and metolachlor (S = 530 mg/L) were in the 60-150 ug/L range, whereas chlorpyrifos (S = 0.4 mg/L) and pendimethalin (S = 0.3 mg/L) were in the 0.6-2.5 g/L range. Total losses of the pesticides in the 193 days amounted to 2.7% (atrazine), 1.1% (metolachlor), 0.01% (chlorpyrifos), and 0.13% (pendimethalin) of their respective application rates. A compaction layer prevented the subsurface drains from influencing consistently water flow from the plots. Chemical loss data from the 1995 season will also be presented.