Comparison of RUSLE model and UAV-GIS methodology to assess the effectiveness of temporary ditches in reducing soil erosion

Comparison of RUSLE model and UAV-GIS methodology to assess the effectiveness of temporary ditches in reducing soil erosion

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  Comparison of RUSLEmodel and UAV-GIS methodology to assess the effectiveness of temporary ditches in reducing soil erosion Ulderico Neri, Rosa Francaviglia, CREA, Council for Agricultural Research and Economics Research Centre for Agriculture and Environment, Rome, Italy Work done under the Project MO.NA.CO. funded by the Ministry of Agricultural, Food and Forestry Policies (MiPAAF) . We thank Paolo Bazzoffi coordinator of the project. y = 1.0346x - 3.0593 R² = 0.9474 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 ErosionUAV-GIS Erosion RUSLE Fig. 3: Visual demonstration of the effectiveness of temporary ditches in interrupting the rills Fig. 4: Erosion (t ha-1 period-1) Treatment Observation start Observation end Period (months) Slope(%) Slopelength (m) Plotarea(ha) rills(m3) (tha-1period-1) Periodrainfall (mm) RUSLE Factors RUSLE_GIS onDEM20 meters (tha-1period-1) R K C P Counterfactual Basin13 16 Nov. 2012 27 Feb. 2013 3,4 15,4 136,1 1,58 103,75 87,6 372,8 6580,82 0,054 1,00 1,00 79,38 Factual Basin13 16 Nov. 2012 28 Feb. 2013 3,5 13,8 147,7 1,72 60,56 43,9 372,8 6580,82 0,054 1,00 1,00 57,22 Factual Basin14 19 Sep. 2014 23 Nov. 2014 2,2 13,2 142,1 2,50 5,57 2,8 210,9 9486,20 0,054 1,00 1,00 3,12 Counterfactual Basin14 19 Sep. 2014 23 Nov. 2014 2,2 13,8 218,9 2,45 24,27 12,4 210,9 9486,20 0,054 1,00 1,00 13,9 Factual Plot13 16 Nov. 2012 27 Feb. 2013 3,4 12,4 123,7 0,13 0,65 6,4 372,8 6580,82 0,054 1,00 1,00 n.a. Counterfactual Plot13 16 Nov. 2012 28 Feb. 2013 3,5 13,5 126,0 0,11 3,01 34,0 372,8 6580,82 0,054 1,00 1,00 n.a. Factual Plot14 19 Sep. 2014 23 Nov. 2014 2,2 12,4 123,7 0,18 2,08 14,0 210,9 9486,20 0,054 1,00 1,00 n.a. Counterfactual Plot14 19 Sep. 2014 23 Nov. 2014 2,2 13,5 126,0 0,12 4,19 45,0 210,9 9486,20 0,054 1,00 1,00 n.a. Table 1 - n.a., not applicable due to the small plot size INTRODUCTION The European Cross-Compliance mechanism set up within the CAP provides payments to farmers under the condition that specific Standards for Good Agricultural and Environmental Conditions (GAECs) are respected. GAEC standard 5 requires the “Realization of temporary ditches” in sloping lands so that the collected rainwater maintains a speed not compromising the function of the ditch itself and is carried away into the permanent channels. Monitoring the effect of temporary ditches is necessary for two purposes: - evaluate the environmental effectiveness of GAEC standard 5 - calibrate the soil erosion prediction models commonly adopted, i.e. the RUSLE chosen by the European Evaluation Network for Rural Development vs Photogrammetry acquired by Unmanned Aerial Vehicles (UAV), integrated by post processing. METHODOLOGY Monitoring was made in two years of observations at Tor Mancina farm (Monterotondo, Rome) (N 42° 05’ 43.09’’; E 12° 38’ 04.83”), at 43 m a.s.l. Soils derive from volcanic materials and are classified as Typic Argixeroll (Soil Survey Staff). The survey was performed with a UAV Falcon 8 (Astec, Germany), equipped with a high-resolution camera. The volume of rills was determined in ESri ArcGis 10.0. In the farm the monitored parameters were: - Erosion, measured with UAV-GIS methodology and estimated with the RUSLE in conditions of implementation of the Standard (Factual) and in conditions of non-implementation (counterfactual) on a wheat crop (Fig. 1-2). - Total volume of rills (m3). RESULTS AND DICUSSION Table 1 shows the summary of monitoring results. Period represents the time between the date of execution temporary ditches (after wheat sowing) and the date of the survey with UAV. Table 1 also shows the characteristics of monitoring sites, the amount of rainfall during the observation period, the volume of rills (m3) and the RUSLE factors applied through GIS. The last column on the right shows the RUSLE estimates by using resampled DEMs with cell size of 20 meters (the original cell size of DEM is 4,7cm). Fig. 1, 2 and 3 show the effectiveness of the temporary ditches to decrease the formation of rills. Comparing the UAV-GIS methodology (27.34 t ha-1 period-1) and the RUSLE in GIS it was possible to validate the RUSLE model (36.83 t ha-1 period-1). Despite the limited observations the performance of the RUSLE resulted satisfactory as shown by the linear regression. (Fig. 4). CONCLUSIONS Results have shown that temporary ditches were effective in decreasing erosion, on average by 62,5%, from 44.75 t ha-1 to 16.78 t ha-1. This result is above the limit of tolerable erosion (6 t ha-1 year-1) set by the OECD and confirm the findings of a previous trial conducted in Guiglia (Modena, northern Italy) on small basins planted with corn, where ditches significantly decreased soil erosion by 94%, from 14.4 t ha-1 year-1 to 0.8 t ha-1 year-1. From results of soil erosion acquired through the application of the methodology UAV-GIS and the application of the RUSLE model in GIS (Table 1) it was possible validate the predictive RUSLE model. Fig.1: Soil erosion in plot comparisons Fig. 2: Soil erosion in basins comparisons FactualCounterfactual