|Bingner, Ronald - Ron|
Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/5/2008
Publication Date: 7/21/2008
Citation: Gordon, L.M., Bennett, S.J., Alonso, C.V., Bingner, R.L. 2008. Modeling Long-Term Soil Losses on Agricultural Fields Due to Ephemeral Gully Erosion. Journal of Soil and Water Conservation, 63(4): 173-181. 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: It is now recognized worldwide that soil erosion on agricultural fields due to ephemeral gullies may be greater than those losses attributed to sheet and rill erosion processes. Yet it is not known whether the common practice of repairing or obliterating these gullies during annual tillage activities exacerbates or mitigates soil losses over long time periods. Here, a numerical model is used to demonstrate the potential effects of annual tillage on cumulative soil losses from four geographic regions plagued by ephemeral gullies as compared to no-till conditions where the gullies are free to grow and evolve over time and space. Historical precipitation data and field measurements were compiled for specific sites in Belgium, Mississippi, Iowa, and Georgia, and the model simulated ephemeral gully development and evolution during the growing seasons over a continuous ten-year period. When agricultural fields are not tilled annually, the simulations suggest that gullies attain their maximum dimensions during the first few years in response to several relatively large runoff events. During subsequent runoff events, the gullies no longer erode their channels significantly, and soil losses due to gully erosion decrease markedly. When agricultural fields are tilled annually, the ephemeral gully channels are reactivated, thus causing significant soil losses each year in response to runoff events. Over the ten-year simulation, the modeling results suggest that erosion rates in these four geographic regions can be 250 to 450% greater when gullies are tilled and reactivated annually as opposed to the no-till condition. These results reveal that routine filling of ephemeral gully channels during tillage practices may result in markedly higher rates of soil loss as compared to allowing these gullies to persist on the landscape, demonstrating a further advantage of adopting no-till management practices.