Evaluation of Erosion Risk with Stakeholders using RUSLE Methodology and Publicly Available Information in a Large Olive Producing Area in Southern Spain

Abstract

This communication presents the current results of an ongoing cooperative project with olive farmers of the Protected Appellation of Origin Estepa (hereafter DOP Estepa), in Southern Spain, encompassing approximately 40,000 ha of olives under different soil management systems, from bare soil using tillage or herbicides to temporary cover crops. The purpose of this project is to evaluate water erosion risk at the farm plot unit using freely available information and RUSLE methodology, to detect areas with greater risk of soil erosion, and contribute to the improvement of soil conservation in the DOP Estepa. For this, a GIS was set up using QGIS v.3.4.11. This GIS was used to aggregate spatial information to apply RUSLE (Dabney et al., 2012). The key layers of spatial information were: a raster DEM at 25m x 25m grid spacing from the Spanish National Center for Geographic Information, a vector map containing farm plot boundaries, land use and tree density from Common Agricultural Policy (hereafter SIGPAC), a vector soil map classification from the Andalusian Repository of Environmental Information (hereafter REDIAM), a raster map of annual rainfall erosivity also derived from REDIAM, and Sentinel-2-L-2A images (EOS, 2020). All this information was used, as follows, to develop a raster map at a 25m x 25m grid spacing of the different RUSLE parameters. The LS factor was obtained using the algorithms accessible from QGIS based on Desmet and Govers (1996), the K factor was determined based on the soil classification using the calibration for these soil types made by Gómez et al. (2014), and R was directly taken from the map provided by REDIAM. The C factor was calculated for the most common bare soil and cover crop management techniques implemented in the area (previously identified through questionnaires to farmers; Gómez et al., 2021) using the ORUSCAL tool (Biddoccu et al., 2020). The use of bare soil or temporary cover crop at the plot level was identified comparing differences in the enhanced vegetation index (EVI) between winter 2019 and summer 2020 Sentinel images using the methodology for olive orchards described in Guzmán et al. (2022). Preliminary results suggest that approximately 8% of the olive plots present average annual soil losses below 1 t ha^-1 and 94% below 10 t ha^-1. We will also report on the progress to create a tool to update these predictions and to provide access to farmers based on annual updates on farming practices at each farm, and plans to validate erosion risk with in-field evaluations based on management and visual erosion symptoms calibrated and validated for olive orchards in the region.