The index addresses water erosion on agricultural lands. The occurrence and intensity of soil erosion largely depend on the occurrence, intensity and amount of precipitation, topography, soil type and characteristics, slope length and gradient, agricultural practices, and potential anti-erosion protective measures.

It is expected that the annual average erosion rate varies according to the occurrence, intensity and force of precipitation in the given year, changes in land cover, the type of agricultural practices on individual plots, and implemented anti-erosion measures.

Assessing Erosion in Slovenia using More Accurate Data

The RUSLE method reliably estimates erosion intensity on slopes of less than 50% (< 26.6°). However, the estimates for steeper slopes are less reliable but still informative. Regarding the land use categories, erosion is most pronounced in permanent crops (average of 15.2 t/ha), on lands with intensive soil cultivation, such as fields and gardens (6.4 t/ha), while the overall erosion on all types of grassland is slightly lower (5.7 t/ha). Calculations for each type of land use show that erosion is most prominent in lands with exposed and tilled soil. The highest erosion occurs in olive groves (41.4 t/ha) and vineyards (29.3 t/ha), while it's somewhat lower in intensive orchards (10.0 t/ha) and even lower in arable lands (6.4 t/ha). For olive groves and vineyards, and to a lesser extent for intensive orchards, it is estimated that the RUSLE calculations may be overestimated because a significant portion of these agricultural crops are on terraces. Terraces were not considered in the calculations because there is not enough precise data on terrace usage in Slovenia. Similarly, precise data on grass cover in permanent crops could reduce erosion estimates for these land uses.

For permanent grasslands, erosion is estimated to be relatively high (5.8 t/ha), which is understandable due to the higher proportion of steep slopes in these areas. As expected, erosion rates in forests are significantly lower. Erosion in forests across Slovenia is estimated to be considerably higher (0.37 t/ha) than in forests on slopes with gradients of less than 50% and in flat areas (0.25 t/ha). The prohibition of clear-cutting also contributes to the low erosion estimates.

The average annual erosion in Slovenia is estimated at 3.2 t/ha. For 82.9% of the Slovenian territory on flatlands and slopes with gradients of less than 50%, it is estimated at 2.6 t/ha. A very high percentage of forests (59%) contributes to the relatively low erosion estimate for the entire country.

The results of erosion intensity modeling using more accurate data significantly differ from rough estimates suitable for a continental scale.

Erosion Assessment within Europe

Within the EC Joint Research Centre (JRC), the European Soil Data Centre (ESDAC) conducted erosion modeling and published an extensive erosion assessment for most EU countries or a significant part of the continent in 2015 (Panagos et al., 2015). The results of this erosion modeling indicate that Slovenia ranks second among EU member states in terms of annual erosion, with an average of 7.43 t/ha/year of eroded soil in all land uses. They explain that Slovenia's high erosion rate is due to the intense erosivity of rainfall and steep topography. Italy has a higher average annual erosion rate (8.46 t/ha), while Austria ranks third with 7.19 t/ha. For arable land in Slovenia, it is estimated to 4.63 t/ha per year. The Primorsko-Notranjska, SE Slovenia, and Savinjska statistical regions have an average annual erosion rate of 10 – 20 t/ha, again among the highest in the EU; the western part of Slovenia, along with the Osrednjeslovenska region, ranges from 5 – 10 t/ha; Posavska, Podravska, and Pomurska regions are between 2 – 5 t/ha.

These figures significantly exceed the estimates and general opinion of erosion intensity in Slovenia.