Runoff of herbicides from cropped and uncropped plots with different slopes

Abstract

Losses of the selective herbicides alachlor, metolachlor and EPTC were monitored in runoff waters from experimentally controlled clay-soil plots cultivated with corn. Conditions were selected to simulate agricultural practices employed in the Mediterranean region. Plots were selected to have differing slopes, and uncultivated (control) areas were simultaneously monitored. The duration of the experiment was one year. The surface slopes of the plots, were 0, 1, 2.5, and 5%. Soil erosion was shown to increase with slope from 470 to 1350 kg/ha for slopes of 0 to 5% respectively and the corresponding runoff of surface water was from 6.5 to 26.4% of the total rainfall. Surface runoff herbicide concentrations were highest in the first flush events following the two herbicide applications. Initial concentrations were related to the time that had elapsed between the herbicide application and the runoff event. The maximum concentrations of herbicides in runoff were observed for the plots with the greatest slope (5%) reaching 142 and 154 µg/L for alachlor, 135 and 221 µg/L for metolachlor, and 765 and 1.071 µg/L for EPTC, in tilled and untilled plots, respectively. Cumulative losses of alachlor in surface runoff from tilled and untilled plots (with a slope of 5%) were estimated to be 0.27 and 0.47% of the initially applied active ingredient, respectively. For plots with a slope of 0%, the percentage loss dropped to 0.03 and 0.06% respectively. For metolachlor, the corresponding values from tilled and untilled plots were 0.42 and 1.09% (for a slope of 5%), and 0.08 and 0.16% (for a slope of 0%). In the case of EPTC, the corresponding values from tilled and untilled plots were 0.44 and 0.63% (slope 5%), and 0.04 and 0.07% (slope 0%). Analyses of soil samples from the plots during the period enabled dissipation kinetics to be studied. Results showed that corn cultivation decreased the half-lives of the herbicides [when compared to the control (uncultivated) fields] as follows: for alachlor from 16.7 to 10 days, for metolachlor from 22.3 to 13.3 days and for EPTC from 17.8 to 8 days.

The slope of the soil surface, the compound's solubility and its sorption characteristics are identified as the major parameters that influence alachlor, metolachlor and EPTC transport in the present study.

Keywords:

• Herbicides
• Alachlor
• Metolachlor
• EPTC
• Runoff
• Slope
• Corn cultivation
• Plots

Acknowledgements

This research has been supported by the General Secretariat of Research and Technology – Athens, Program YPER (Contract: 94-YP-109/15203/14-12-1995). The authors wish to thank the staff of the Agricultural Research Station of Ioannina for their help and cooperation throughout the course of this study.