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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED ASSESSMENT AND ANALYSIS OF PHYSICAL LANDSCAPE PROCESSES THAT IMPACT THE QUALITY AND MANAGEMENT OF AGRICULTURAL WATERSHEDS

Location: Watershed Physical Processes Research Unit

Title: Modeling the contribution of ephemeral gully erosion under different soil managements: A case study in an olive orchard microcatchment using the AnnAGNPS model

Authors
item Taguas, E -
item Yuan, Y -
item Bingner, Ronald
item Gomez, J -

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 3, 2012
Publication Date: July 2, 2012
Repository URL: http://handle.nal.usda.gov/10113/54337
Citation: Taguas, E.V., Yuan, Y., Bingner, R.L., Gomez, J.A. 2012. Modeling the contribution of ephemeral gully erosion under different soil managements: A case study in an olive orchard microcatchment using the AnnAGNPS model. Catena. 98:1-16.

Interpretive Summary: In Spain, few studies have been carried out to explore the erosion processes other than interril and rill erosion, such as gully and ephemeral gully erosion. Most of the available studies have evaluated erosion at plot scale. A study about the environmental and economic impact of different soil management strategies, spontaneous grass cover with and without gully control or conventional tillage with and without gully control, was undertaken based on experimental results obtained in a small 6.1 hectare olive crop watershed. Initially, over the course of two years, rainfall-runoff-sediment load was recorded for 34 events under the current management practices for calibration of the US Department of Agriculture AnnAGNPS watershed pollutant model on event and monthly scales providing suitable adjustments of runoff, peak flow and sediment loads. Ephemeral gullies were identified using aerial photographs and field work. Simulations of ephemeral gully generated under tillage operations based on a datasets from a bibliographical review were used to compare different scenarios for a 10 year-analysis. Significant differences in sediment sources (rill/interrill erosion and ephemeral gullies) were evaluated between grass cover where 46% of the sediment load was from gully contributions and conventional tillage where 19% of the sediment load was from gully contributions, which would provide an optimization of the environmental and economic efforts in each case. Annual costs associated with soil losses were estimated at less than 1 Euro per hectare per year. Grass cover was the most profitable alternative management practice. Despite the additional reduction in soil losses of the SCGC approach, the larger cost due to its implementation and the minor effect on yield losses in the medium term suggests that without additional support (like subsidies for gully control measures) farmers would not have a clear incentive to adopt these conservation practices. As more ephemeral gully data is collected, improvements to watersheds will provide better tools in conservation practice planning.

Technical Abstract: In Spain, few studies have been carried out to explore the erosion caused by processes other than interril and rill erosion, such as gully and ephemeral gully erosion, especially because most of the available studies have evaluated the erosion at plot scale. A study about the environmental and economic impact of different soil management strategies, spontaneous grass cover with and without gully control (SC/SCGC) or conventional tillage with and without gully control (T/TGC), was undertaken based on the experimental results obtained in an olive crop microcatchment of 6.1ha. Initially, two years of rainfall-runoff-sediment load data series (34 events) recorded under the current management (SCGC) was used for the calibration of the AnnAGNPS model on event and monthly scales providing suitable adjustments of runoff, peak flow and sediment loads (E >70, r >0.85). Ephemeral gullies were also identified using aerial ortophotography and field work. The module of the AnnAGNPS model to simulate ephemeral gully generation and the tillage operations based on a bibliographical review was used to compare different scenarios and to perform a 10 year-analysis. The results showed mean runoff coefficients of 10.0% for SC/SCGC and of 3.2% for T/TGC while the average sediment loads were 2.0 t.ha-1year-1 (SCGC), 3.5 t.ha-1year-1 (SC), 3.3 t.ha-1year-1 (TGC) and 4 t.ha-1year-1 (T). Significant differences in sediment sources (rill/interrill erosion and ephemeral gullies) were evaluated between SC (46% of gully contribution) and T (19% of gully contribution), which would provide an optimization of the environmental and economic efforts in each case. Finally, annual costs associated with soil losses were estimated (< 1 €.ha-1year-1). SC was the most profitable alternative of soil management. Despite the additional reduction in soil losses of the SCGC approach, the larger cost due to its implementation and the minor effect on yield losses in the medium term suggests that without additional support (like subsidies for gully control measures) farmers have not a clear incentive to its application.

Last Modified: 4/20/2014
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