## 4 Discussion  
### Erosion Rates in Tierras de Barros within a Mediterranean Perspective  
Since the pioneering studies carried out in Chile and Germany using erosion plots and sediment collectors during the 70 s, the number of publications related to soil erosion in vineyards have drastically increased, reaching the peak since 2000 [52]. This is because of the interest in surveying the soil erosion rates and finding sustainable management practices [38; 53]. However, there is much less innovation on new methods and techniques to measure the soil erosion rates, although there is a lack of surveys in many vineyards of the world. A wide spectrum of methods has been applied in vineyards but there is a lack of long-term soil erosion studies, which is also found in other crops [54; 55]. The research at the Tierra de Barros study site confirms what the scientific community found in other vineyards: high soil mobilization rates (71.2 Mg ha\({}^{-1}\) yr\({}^{-1}\)) which are not sustainable [56] if we compare these results to the other studies. In a meta-analysis, [PERSON] et al. [19], considering 1350 experimental plots of different land uses areas, found that vineyards reached the highest erosion rates in Europe with 12.2 Mg ha textsuperscript\(-1\) yr\({}^{-1}\). Several investigations carried out in north Spanish vineyards affected by gullies registered soil mobilizations higher than 200 Mg ha\({}^{-1}\) yr\({}^{-1}\) during extreme rainfall events [23; 57; 58].  
In Italy, we can observe some recent comparable investigations published in 2019 but with soil erosion rates lower than in the Tierra de Barros. For instance, [PERSON] et al. [59] assessed the soil tillage erosion rate in a Sicilian vineyard using a \({}^{13}\)C natural abundance tracer registering 9.5 \(\pm\) 1.2 Mg ha\({}^{-1}\) yr\({}^{-1}\). On the other hand, using the USLE (Universal Soil Loss Equation) for the same area, [PERSON] et al. [38] over the 10-year period of observation quantified up to 3 Mg ha\({}^{-1}\) with a maximum of 13.2 Mg ha\({}^{-1}\) in 2014. In addition, in Italy, [PERSON] et al. [60] applying the Revised Universal Soil Loss Equation (RUSLE) in 24 terraced vineyards located in north-eastern Italy calculated from 53.9 to 69.5 Mg ha\({}^{-1}\) yr\({}^{-1}\). In the Prosecco viticultural region, [PERSON] et al. [61] modelled a potential soil erosion that could reach 300,180 Mg yr\({}^{-1}\), which represents 43.7 Mg ha\({}^{-1}\) yr\({}^{-1}\). The same authors estimated for a conventional land-management scenario 3.3 kg of soil for every bottle produced but it would be reduced to 1.1 kg per bottle if the total area were completely green land-managed. Therefore, it is clear that mandatory work in order to develop nature-based solutions should be selected by technicians and policymakers and applied by the farmers [5; 62]. The comparison of the Tierra de Barros study site to other Mediterranean vineyards shows that the soil erosion rates are one order of magnitude higher and this is due to the intensification of the production with deep and recurrent tillage. This means that the soil is bare most of the year and then the soil erosion rates are very high and non-sustainable, such as [PERSON] [52] updated recently.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Variables** & **Inter-Row 1** & **Inter-Row 2** & **Inter-Row 3** & **1 + 2** & **1 + 2 + 3** \\ \hline Area m\({}^{2}\) (long \(\times\) width) & 302.4 (2.8 \(\times\) 108 m) & 604.8 (5.6 \(\times\) 108 m) & 907.2 (8.4 \(\times\) 108 m) \\ Number of points & 2016 & & 3960 & 5904 \\ m\({}^{3}\) ha\({}^{-1}\) & 34.8 & 35.7 & 34.7 & 70.1 & 104.2 \\ Mg ha\({}^{-1}\) & 43.2 & 42.8 & 44.8 & 85.5 & 129.2 \\ Mg ha\({}^{-1}\) yr\({}^{-1}\) & 71.4 & 70.8 & 74.0 & 70.7 & 71.2 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Soil mobilization rates obtained using ISUM for one, two, and three plots.