Long-Term Effects of Tillage and Crop Rotation on the Leaching of Nitrate and Pesticides to Shallow Groundwater

by R. S. Kanwar, Iowa State Univ, Ames, United States,
D. E. Stoltenberg, Iowa State Univ, Ames, United States,
R. Pfeiffer, Iowa State Univ, Ames, United States,
D. L. Karlen, Iowa State Univ, Ames, United States,
T. S. Colvin, Iowa State Univ, Ames, United States,
M. Honeyman, Iowa State Univ, Ames, United States,

Document Type: Proceeding Paper

Part of: Irrigation and Drainage


Contamination of groundwater by nitrate-nitrogen (NO3-N) and pesticides is a serious problem and concern in Iowa. The extent of contamination can best be studied on plots with long term tillage and cropping histories. The objective of this study was to conduct field experiments to evaluate the effects of four tillage systems (moldboard plow, chisel plow, ridge tillage, and no-tillage) and two crop rotations (continuous corn and corn-soybean) on the leaching of NO3-N and pesticides to shallow groundwater. Data for 1990 on the transport of atrazine, cyanazine, alachlor, metribuzin, and NO3-N to shallow groundwater were analyzed. The average yearly NO3-N losses with subsurface drainage water ranged from 30.3 to 107.2 Kg/ha. The no-tillage system under continuous corn increased infiltration, decreased NO3-N concentration in groundwater, and increased total NO3-N and herbicide losses to groundwater. Atrazine, alachlor, cyanazine, and metribuzin seem to move preferentially through macropores to groundwater after heavy rainfall events. More data on NO3-N and pesticide leaching will be collected in the coming years which will help us in establishing cause-effect relationships.

Subject Headings: Crops | Rotation | Leaching | Nitrates | Pesticides | Groundwater | Field tests | Subsurface drainage | Iowa | United States

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