The North Appalachian Experimental Watershed near Coshocton, Ohio, USA 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. Small (0.5 to 1 ha), single-practice, watersheds 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 residual herbicides from these watersheds was the result of the top five transport events, most of which occurred within 100 days after herbicide application. Thus, management practices must be devised that reduce herbicide concentrations from these infrequent events in order to reduce losses to acceptable levels. A four-year study indicated that growing transgenic, herbicide-tolerant corn and soybean and replacing some of the residual herbicides normally used to produce these crops with strongly sorbed contact herbicides resulted in concentrations of the contact herbicides in surface runoff well below their drinking water standards. Multi-tiered conservation systems in which practices such as grassed waterways and filter strips are used in combination with conservation tillage need to be developed to further reduce the impact of extreme events. Furthermore, sampling strategies and transport models must accurately account for such events in order to properly measure and predict herbicide losses. Long-term studies are essential to fully evaluate the effects of conservation systems on herbicide losses in surface runoff.
Link to Presentation (pdf; 8MB)
Martin Shipitalo - Martin Shipitalo is a Research Soil Scientist at the USDA-ARS North Appalachian Experimental Watershed near Coshocton, Ohio. His research is centered on evaluating the effects of conservation tillage on soil and water quality with an emphasis on the role of earthworm activity. He obtained by BS and MSc in soil science from The Ohio State University and his PhD from the University of Guelph. He currently serves on the editorial board of Applied Soil Ecology.