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TECHNICAL REPORTS

Organic Compounds in the Environment

Combined Effects of Constant versus Variable Intensity Simulated Rainfall and Reduced Tillage Management on Cotton Preemergence Herbicide Runoff

^a USDA-ARS, Southeast Watershed Research Laboratory, Box 748, Tifton, GA 31793
^b USDA-ARS, J. Phil Campbell, Sr., Natural Resource Conservation Center, Watkinsville, GA
^c Dep. Crop and Soil Science, University of Georgia, Coastal Plain Experiment Station, Tifton, GA
^d USDA-ARS, Crop Protection and Management Research Unit, Box 748, Tifton, GA 31793

^* Corresponding author (tpotter{at}tifton.usda.gov)

Received for publication December 1, 2005. Pesticide runoff research relies heavily on rainfall simulation experiments. Most are conducted at a constant intensity, i.e., at a fixed rainfall rate; however, large differences in natural rainfall intensity is common. To assess implications we quantified runoff of two herbicides, fluometuron and pendimethalin, and applied preemergence after planting cotton on Tifton loamy sand. Rainfall at constant and variable intensity patterns representative of late spring thunderstorms in the Atlantic Coastal Plain region of Georgia (USA) were simulated on 6-m² plots under strip- (ST) and conventional-tillage (CT) management. The variable pattern produced significantly higher runoff rates of both compounds from CT but not ST plots. However, on an event-basis, runoff totals (% applied) were not significantly different, with one exception: fluometuron runoff from CT plots. There was about 25% more fluometuron runoff with the variable versus the constant intensity pattern (P = 0.10). Study results suggest that conduct of simulations using variable intensity storm patterns may provide more representative rainfall simulation-based estimates of pesticide runoff and that the greatest impacts will be observed with CT. The study also found significantly more fluometuron in runoff from ST than CT plots. Further work is needed to determine whether this behavior may be generalized to other active ingredients with similar properties [low K_oc (organic carbon partition coefficient) 100 mL g^–1; high water solubility 100 mg L^–1]. If so, it should be considered when making tillage-specific herbicide recommendations to reduce runoff potential.

Abbreviations: AWC, antecedent water content • CT, conventional tillage • MDL, method detection limit • NT, no tillage • OC, organic carbon • %RPD, relative percent deviation • RSD, percent relative standard deviation • SD, standard deviation • ST, strip tillage

This article has been cited by other articles:

				T. L. Potter, C. C. Truman, T. C. Strickland, D. D. Bosch, and T. M. Webster Herbicide Incorporation by Irrigation and Tillage Impact on Runoff Loss J. Environ. Qual., May 1, 2008; 37(3): 839 - 847. [Abstract] [Full Text] [PDF]

				C.C. Truman, T.C. Strickland, T.L. Potter, D.H. Franklin, D.D. Bosch, and C.W. Bednarz Variable Rainfall Intensity and Tillage Effects on Runoff, Sediment, and Carbon Losses from a Loamy Sand under Simulated Rainfall J. Environ. Qual., August 31, 2007; 36(5): 1495 - 1502. [Abstract] [Full Text] [PDF]