Effectiveness of the GAEC cross-compliance standard Short-term measures for runoff water control on sloping land (temporary ditches and grass strips) in controlling soil erosion

Abstract

The agronomic measures made obligatory by the cross-compliance Standard Temporary measures for runoff water control on sloping land included in the Ministry of Agricultural, Food and Forestry Policies (MiPAAF) decree on cross compliance until 2008, and by Standard 1.1 Creation of temporary ditches for the prevention of soil erosion in the 2009 decree, certainly appear to be useful for the control of soil erosion and runoff. The efficacy of temporary drainage ditches and of grass strips in controlling runoff and erosion has been demonstrated in trials conducted in field test plots in Italy. When level temporary drainage ditches are correctly built, namely with an inclination of not more than 2.5% in relation to the maximum hillslope gradient, they allow the suspended sediment eroded upstream to settle in the ditches, retaining the material carried away on the slope and, as a result, reducing the quantity of sediment delivered to the hydrographic network. In particular, among all the results, the erosion and runoff data in a trial conducted in Guiglia (Modena) showed that in corn plots, temporary drainage ditches reduced soil erosion by 94%, from 14.4 Mg ha-1 year-1 (above the limit established by the NRCS-USDA of 11.2 Mg ha-1 year-1) to 0.8 Mg ha-1 year-1 (within the NRCS limit and also within the more restrictive limit established by the OECD of 6.0 Mg ha-1 year-1). With respect to the grass buffer strips the most significant research was carried out in Volterra. This research demonstrated their efficacy in reducing erosion from 8.15 Mg ha-1 to 1.6 Mg ha-1, which is approximately 5 times less than the erosion observed on bare soil. The effectiveness of temporary drainage ditches was also assessed through the application of the Revised Universal Soil Loss Equation (RUSLE) erosion model to 60 areas under the control of the Agency for Agricultural Payments (AGEA) in 2009, comparing the risk of erosion in these sample areas by simulating the presence and absence of drainage ditches at a distance of 80 metres from each other as required by the Standard. The results of the scenario analysis showed that the presence of ditches on average decreases erosion by 67%. To sum up, the Standard was found to be effective from a hydraulic point of view, as the results have demonstrated the adequacy of temporary ditches for the control of runoff water. Another important result of this study was the production of a simple equation that can be directly used by farmers or, more realistically, by the farm advisory system to provide farmers with the information necessary for the realisation of temporary drainage ditches (depth and section that can be obtained with the most widespread types of ditch diggers) so that these ditches are effective and maintain their hydraulic efficacy throughout the entire cropping period. This equation would also be useful for cross-compliance control by the AGEA and regional control bodies.