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Modeling the Contribution of Ephemeral Gully Erosion Under Different Soil Management in An Olive Orchard Microcatchment Using AnnAGNPS Model
Citation:
Taguas, E. V., R. L. Bingner, Y. YUAN, AND J. A. Gomez. Modeling the Contribution of Ephemeral Gully Erosion Under Different Soil Management in An Olive Orchard Microcatchment Using AnnAGNPS Model. CATENA. Elsevier Science, New York, NY, 98:1-16, (2012).
Impact/Purpose:
At a global scale soil erosion is a major environmental problem resulting, among other issues, in a threat to the sustainability of agricultural production and the quality of surface waters in large regions of the world (Wilkinson and McElroy, 2007). Water and aeolian erosion affects 16% of European territory, with the Mediterranean countries of Spain and Portugal facing the most serious risk of erosion, (PESERA, 2004). Due to the severe sloping nature of the landscape, high erosion rates can be expected in agricultural regions in Spain planted with vines, almond and olive trees, which are very important to the Spanish economy. These crops are common in precisely the areas of Spain most prone to desertification (De Santiesteban et al., 2006).
Description:
In Spain, few studies have been carried out to explore the erosion caused by processes other than interrill 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 orthophotography 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-1), 3.5 t.ha-1)year-1 (SC), 3.3 t.ha-1)year-1), (TGC) and 4 t.ha-1)year-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-1)year-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.