Effectiveness and feasibility of different management practices to reduce soil erosion in an agricultural watershed

Abstract

Erosion is the most widespread form of soil degradation in Europe. EU Member States are called to identify areas prone to high risk of soil erosion and to adopt Best Management Practices (BMPs) to decrease land degradation. This study is aimed at identifying effective BMPs and their economic feasibility for controlling soil erosion in south-central Italy where lands are largely cultivated with winter wheat. The Soil and Water Assessment Tool (SWAT) was applied to simulate the baseline hydrologic and soil erosion processes of the Carapelle basin in the Puglia region, Italy. Calibrated sediment loads were reasonably accurate when statistically evaluated against measured data (R2 = 0.5, NSE = 0.5, PBIAS=−2.8 %). The model performed equally well for simulating stream flow rates (R2 = 0.6, NSE = 0.6, PBIAS = 5.3 %). The model maintained reliable performance during the validation period as well. Average annual specific sediment load was estimated 5.95 t ha-1 yr-1 mostly contributed by cultivated croplands. Based on regional agricultural policies, four management scenarios were implemented using the calibrated SWAT model: contour farming (BMP1), no tillage (BMP2); reforestation (BMP3) and contour farming and reforestation (BMP4). A threshold of sediment yield greater than 10 t ha-1yr-1 was selected to discretize target treatment areas where these BMPs were applied. Result show that combining contour farming and reforestation (BMP4) was the most effective (38 % reduction; from 5.95 to 3.70 t ha-1) for erosion control, followed by BMP2 (29 %; from 5.95 to 4.20 t ha-1), BMP1 (22 %; from 5.95 to 4.61 t ha-1) and BMP3 (15 %; from 5.95 to 5.04 t ha-1). An analysis of the farmer return-production cost ratio (FR/PC) indicated that the baseline (conventional tillage) and BMP1 were both economically sustainable in areas with slope <20 % (FR/PC = 1.12 and 1.11, respectively). BMP2 received the highest FR/PC rating of 1.67 in areas with slope <20 %. The baseline scenario had no economic advantage (FR/PC = 0.93) in steep slope areas. BMP3 was ranked at the top (FR/PC = 1.49) followed by BMP2 (FR/PC = 1.41) in areas with slope>20 %. The results show that a program of measures can be effective for controlling soil erosion but it must be implemented over long time frames and it requires relevant investments from the public and private sectors.