Integrated Soil, Crop and Water Management System to Abate Herbicide and Nitrate Contamination of the Great Lakes

Abstract

Corn management practices, incorporating annual ryegrass intercrop, conservation tillage and water table management, were evaluated to reduce herbicide and N0⁻₃ losses through surface runoff and tile drainage. The integrated management system being developed at Harrow in S.W. Ontario reduced herbicide input 50% by banding the chemical over the seed row. Runoff events close to herbicide application contained high concentrations of atrazine, metribuzin and metolachlor. However, the volume of runoff was low during the 1991 growing season, therefore herbicide loss was low (<2% of applied). The three herbicides rapidly dissipated in the soil so that subsequent runoff events transported little herbicide in the runoff water. The total quantity of de-ethyl atrazine loss was lower from soil saver than moldboard plow. No water table control or intercrop effects were found in 1991 for herbicide loss because of the drought Tile drainage resulted in a greater volume of water and loss of N0⁻₃ than with surface runoff. Consequently, over 97% of the total N0⁻₃ loss occurred through tile drainage. The flow weighted N0⁻₃ concentration in tile drainage water was 22.5 mg N L⁻¹ for the drainage treatments and 15.1 mg N L⁻¹ for the water table control treatments from Nov. 1, 1991 till April 30, 1992. During this time period, N0⁻₃ loss through tile drainage was 57.8 kg N ha⁻¹ from the drainage treatments and 36.3 kg N ha⁻¹ from the water table control treatments. Therefore, the water table control treatment reduced the flow weighted N0⁻₃ concentration in tile drainage water by 33% and total N0⁻₃ loss by 37%. The water table control treatments combined with soil saver tillage resulted in lower concentrations and losses of N0⁻₃ than with any other treatments.