LONG-TERM WATERSHED STUDIES OF CONSERVATION TILLAGE HIGHLIGHT THE IMPACT OF INFREQUENT EVENTS ON SEDIMENT AND HERBICIDE TRANSPORT

Authors: Shipitalo, Martin; Owens, Lloyd; Bonta, James - Jim

Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2006
Publication Date: 10/11/2006
Citation: Shipitalo, M.J., Owens, L.B., Bonta, J.V. 2006. Long-term watershed studies of conservation tillage highlight the impact of infrequent events on sediment and herbicide transport [abstract]. Soil and Water Conservation Society Meeting, "Managing Agricultural Landscapes for Environmental Quality - Strengthening the Science Base". Oct. 11-13, 2006, Kansas City, MO.

Interpretive Summary:

Technical Abstract: The North Appalachian Experimental Watershed near Coshocton, Ohio was established in the 1930’s to develop, evaluate, and refine conservation practices that reduce runoff and erosion under the hilly, humid conditions of the Appalachian region of the US. Small (0.5 to 1 ha), single-practice, watersheds comprised of sandstone- and shale-derived residual soils are used to evaluate the interaction of management, climate, and soils. This extensive database allows us to evaluate the impact of infrequent events on the effectiveness of various conservation practices. In a 28-year period, an average of 25% of the soil loss from nine, moldboard-plowed watersheds in a 4-year corn/wheat/meadow/meadow rotation was due to the single largest erosion-producing event. The five largest events produced an average of 66% of the soil loss. These events were the result of severe storms. While conservation tillage practices can dramatically reduce soil loss attributable to such storms, a few, infrequent events still dominate sediment transport. In a six-year period an average of 55% of the soil loss from seven watersheds (2 chisel-plowed, 2 no-till, 3 shallow -disked) was attributable to the five largest events, even though these events accounted for only 17% of the total runoff volume. Moreover, since herbicides are normally required to control weeds when conservation tillage practices are used, they are also subject to transport in surface runoff. Unlike sediment, however, proximity of runoff to application date had a greater influence on herbicide transport than did storm size. In a nine-year period with nearly 1800 storms, 60-99% of the total loss of four herbicides from these seven conservation tilled watersheds was the result of the top five transport events, most of which occurred with 100 days after herbicide application. Thus, management practices or control measures must be devised that reduce herbicide concentrations from these infrequent events in order to reduce losses to acceptable levels. Furthermore, sampling strategies and transport models must accurately account for such events in order to properly measure and predict herbicide losses. As with sediment loss, long-term studies are needed to fully evaluate the effects of conservation tillage practices on agrochemical losses in surface runoff.