Monitoring soil erosion processes and measuring soil and water yields allow supplying key information to achieve land degradation neutrality challenges. Vineyards are one of the most affected agricultural territories by soil erosion due to human and natural factors. However, the spatial variability of soil erosion, the number of sampling points, and plot size necessary to estimate accurate soil erosion rates remains unclear. In this research, we determine how many inter-rows should be surveyed to estimate the soil mobilization rates in the viticulture area of Tierra de Barros (Extremadura, SW Spain) using the Improved Stock Unearthing Method (ISUM). This method uses the graft union of the vines as a passive biomarker of the soil surface level changes since the time of plantation and inter-row measures. ISUM was applied to three inter-row and four rows of vines (5904 sampling points) in order to determine how many surfaces and transects must be surveyed as all the previous surveys were done with only one inter-row. The results showed average values of soil depletion reaching −11.4, −11.8, and −11.5 cm for the inter-rows 1, 2, and 3, respectively. The current soil surface level descended 11.6 cm in 20 years. The inter-rows 1, 2, and 3 with a total area of 302.4 m² each one (2016 points) recorded 71.4, 70.8, and 74.0 Mg ha⁻¹ yr⁻¹, respectively. With the maximum number of sampling points (5904), 71.2 Mg ha⁻¹ yr⁻¹ were obtained. The spatial variability of the soil erosion was shown to be very small, with no statistically significant differences among inter-rows. This could be due to the effect of the soil profile homogenization as a consequence of the intense tillage. This research shows the potential predictability of ISUM in order to give an overall overview of the soil erosion process for vineyards that follow the same soil management system. We conclude that measuring one inter-row is enough to get an overview of soil erosion processes in vineyards when the vines are under the same intense tillage management and topographical conditions. Moreover, we demonstrated the high erosion rates in a vineyard within the viticultural region of the Tierra de Barros, which could be representative for similar vineyards with similar topographical conditions, soil properties, and a possible non-sustainable soil management system.