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Title: Ephemeral Gullies: To Till or Not to Till?

item GORDON, L
item Alonso, Carlos
item Bingner, Ronald - Ron

Submitted to: International Symposium on Gully Erosion
Publication Type: Proceedings
Publication Acceptance Date: 4/10/2007
Publication Date: 9/17/2007
Citation: Gordon, L.M., Bennett, S.J., Alonso, C.V., Bingner, R.L. 2007. Ephemeral Gullies: To Till or Not to Till? In: Proceedings of the IV International Symposium on Gully Erosion. September 17-19, 2007, Pamplona, Spain, J. Casali and R. Gimenez (eds). Public University of Navarre. p. 54-55.

Interpretive Summary: Ephemeral gullies serve as effective links transferring sediment and associated agrichemicals from upland areas to stream channels. Technology has recently been developed that incorporates state-of-the-art ephemeral gully science within watershed models. This includes the scour that is produced below ephemeral gully headcuts and the rate that the headcuts move up into the agricultural fields after rainfall events. Through the application of tillage operations on a field, the land surface may be disturbed and ephemeral gullies filled in and repaired from previous erosion events. Ephemeral gully processes included within watershed models thus provides a tool that can determine the effect of conservation management practices and changing soil conditions on the development of ephemeral gully erosion. This study, involving four sites, demonstrated that over ten years filling ephemeral gullies on an annual basis during tillage operations produced three times more erosion then if the gullies were left untilled. When ephemeral gullies are present, land managers should acknowledge the implications of repairing ephemeral gullies during tillage operations and consider alternative conservation practices that reduce ephemeral gully erosion separately from those that control sheet and rill erosion, ensuring the long-term productivity of their land.

Technical Abstract: Ephemeral gully erosion is now recognized as a significant, if not dominant source of sediment from agricultural lands worldwide. Ephemeral gullies are typically plowed in and tilled across annually or more frequently, thus restoring the original swale and allowing erosion processes to become reactivated. Mechanized tillage redistributes soil from convex areas to swales in amounts that may exceed soil losses due to water erosion. This ‘conveyer belt’ repeatedly re-supplies concentrated flow zones with erodible material, potentially exacerbating the long-term impacts of ephemeral gully erosion on losses of soil material and crop productivity, as topsoil thickness is reduced not only in the location of the gullies themselves, but across entire fields. Previous studies have extended the basic theoretical framework of the Ephemeral Gully Erosion Model (EGEM) by refining existing components, incorporating additional components, and adapting the model to operate within the USDA Annualized Agricultural Non-Point Source model (AnnAGNPS). Models of ephemeral gully erosion such as EGEM, and now AnnAGNPS, limit the depth of an ephemeral gully channel to the tillage depth or depth to a less-erodible layer (e.g. fragipan). Once evacuated to this depth (through incision and headcut development and migration), channel widening by sidewall erosion dominates and erosion decreases. While the perceived magnitude of ephemeral gully erosion may be masked after gullies are repaired, the action of plowing in these channels reduces topsoil thickness and crop productivity over a much wider area than the channel itself. This study demonstrated that filling ephemeral gullies on an annual basis during tillage operations may be more destructive than realized. These results provide land managers an additional incentive for adopting soil conservation practices such as no-till.