E R O S I O N

in Slovenia

Brief description and evaluation

of significant soil degradation.

April 2022





Acknowledgements

DID YOU KNOW THAT...

This publication is an ad hoc translation of the Slovenian brochure Erozija v Sloveniji - a simplified publication for the general public. It contains a brief interpretation of the EROSION is a natural process that can be greatly

comprehensive report on the 2020 National Soil Erosion Assessment Project.

accelerated by unsustainable soil management?

REPUBLIKA SLOVENIJA

EROSION is the most important form of soil

MINISTRSTVO ZA KMETIJSTVO,

GOZDARSTVO IN PREHRANO

degradation on five of the seven continents?

The authors would like to thank the Ministry of Agriculture, Forestry and Food for funding the project.

EROSION directly and significantly reduces/degrades

soil ecosystem services?

About the publication

successful measures against erosion are quite simple?

Authors: Dr Borut Vrščaj, Janez Bergant, Peter Kastelic, Marjan Šinkovec

in Slovenia erosion is highest on permanent crops,

Editor: Dr Borut Vrščaj

significantly lower on arable land and lowest on

Contributions: Dr Sašo Petan, Msc Tomaž Poje and

grassland?

Geza Grabar

Cover photo: Geza Grabar

Design: JR design

Produced by: GEAart, 2022

Kataložni zapis o publikaciji (CIP) pripravili v Narodni in The electronic publication is available at: www.kis.si univerzitetni knjižnici v Ljubljani

From the Agricultural Institute of Slovenia,

COBISS.SI-ID 106676739

Ljubljana, 2022

ISBN 978-961-6998-55-0 (pdf)



ABOUT EROSION

Soil erosion is a natural geomorphological process of soil detachment and displacement. It can be greatly accelerated by human activities and can be many times greater than under natural conditions.

Erosion (water, wind, and soil erosion) remains the greatest threat to soil in several regions of the world. Measuring erosion is a time-consuming, costly, and organizationally complex process, so erosion risk and its intensity are usually estimated using computer models. Global and regional erosion estimates vary widely depending on the method used. General estimates of soil erosion in field areas are significantly higher (from 8 to nearly 50 t ha-1 year-1) than estimates from regional and global models (2 to 4 t ha-1 year-1). Any erosion assessment should be evaluated based on an acceptable level of soil loss.1

Estimates of the impact of erosion show a 0.4% decrease in crop yields, which is not insignificant given a growing global population. Importantly, soil erosion also leads to a reduction or degradation of ecosystem services and causes economic damage across multiple sectors.

Thus, erosion is not only an agricultural problem, but also an environmental problem with significant economic consequences.

This booklet mainly focuses on erosion on agricultural land. It is known that erosion of agricultural soils can be reduced through adapted tillage, changes and improvements in soil structure, land use adaptation or, if severe, land use change. Measures such as soil conservation, ground cover, planting trees and shrubs, terracing, and several others have been shown to be effective. Yet, we pay too little attention to erosion in Slovenia. This publication presents Figure 1: Erosion in the field after spring rain (photo B. Vrščaj) a first nationwide assessment of erosion in Slovenia using the RUSLE method and selected Erosion in the field in Hoče near Maribor occurred in the spring after short but intense rains in March 2013.

examples of erosion in our agricultural areas.

Trenches formed on heavy, silty, poorly permeable, and partially hydromorphic soils (Planosol on a slight slope) that were up to 40 cm deep in some places. Fine soil particles were carried away by surface water flow into the drainage Borut Vrščaj

ditches and then into the Hočki potok.

1FAO. 2019. Soil erosion: the greatest challenge to sustainable soil management. Rome. 100 pp.

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RUSLE EQUATION

RUSLE

The Revised Universal Soil Loss Equation (RUSLE) is the mathematical model most commonly The Universal Soil Loss Equation (USLE, 1965) is an empirical model for estimating soil loss used to evaluate erosion in the absence of accurate, and long-term measured data on the from water erosion (t ha-1) on land with known precipitation regime, land use (land cover/

amount of soil eroded from standard test plots.

vegetation/agricultural crops), soil type, relief, and soil management practices. The model was developed at the U.S. National Runoff and Soil Loss Data Center based on several 10,000-year RUSLE evaluates erosion intensity based on key erosion factors: Rainfall frequency, intensity, erosion measurements on standardized plots at 49 experimental sites under a variety of soil and duration; soil susceptibility to erosion; slope and length of slopes; land use and land conditions across the United States. The USLE and more modern models are the primary tool cover; protective/anti-erosion control measures and agricultural practices.

for evaluating erosion and establishing erosion control and protection measures in the United States and other countries.

Equation 1: Basic equation for a group of RUSLE models: The Revised Universal Soil Loss Equation (RUSLE, 1978) is a group of related erosion models (RUSLE2, MUSLE) that is an evolution of the original Universal Soil Loss Equation (USLE).

RUSLE is based on the same equation with some erosion factors improved. RUSLE2015

RUSLE: Er = Rf Kf Lf Sf Cf Pf

(Panagos, 2015) is a modified version of the RUSLE model used to produce soil loss estimates for Europe for the reference year 2010. Input factors (rainfall erodibility, soil erodibility, land cover and land use, topography, and soil treatment practices) are modelled using the latest Where:

available pan-European data at 100 m resolution (Figure 2).

Er = erosion – average annual amount of eroded soil per unit area (t ha-1 year-1) Rf = rainfall erosivity factor (MJ ha-1 mm h-1 year-1) The results of RUSLE2015 have significantly improved previous EU erosion estimates that were uncertain due to the lack of highly separable pan-European data, inconsistencies and input Kf = soil erodibility factor (t ha-1 h -1 MJ-1 ha-1 mm-1) data of erosion factors, missing information on agricultural practices and soil treatments, Lf = slope length factor (no units)

and missing data on precipitation intensity. RUSLE2015 is a useful source of information for Sf = slope inclination factor (no units)

simulating the impacts of various development policies at the EU level.

Cf = land cover and land use factor (no units)

Pf = protection factor (no units)

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ASSESSMENT OF SOIL WATER EROSION IN

THE EU AND SLOVENIA BY RUSLE METHOD

Under the Joint Research Centre (JRC) EC, the European Soil Data Centre (ESDAC) conducted erosion modelling and published a comprehensive erosion assessment for most EU countries in 2015 (Panagos et al., 2015).

The erosion modelling results show that Slovenia ranks second among EU members in annual erosion, with an average of 7.43 t/ha/year of eroded soil across all land use types. The publication explains that the erosion rate in Slovenia is high due to high precipitation erosivity and steep topography. Only 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 at 4.63 t/ha per year. The regions: Obalno-Kraška, Southeast Slovenia and Savinjska have an average annual erosion rate of 10-20 t/ha - also one of the highest in the EU. Five regions in western Slovenia have estimated erosion of 5-10 t/ha and Posavska, Podravska and Pomurska 2-5 t/ha. In any case, these are figures far above the estimates of the Slovenian profession and the general opinion about the intensity of erosion in Slovenia.

In view of these values, it should be borne in mind that it is difficult to take into account the peculiarities of erosion factors in individual countries in the continental scale model.

The peculiarities in Slovenia include relatively erosion-resistant loamy but permeable Eutric Cambisols, a high proportion of forest (about 61%), extreme fragmentation of agricultural Figure 2: Erosion assessment model for the EU country area (Panagos Et Al., 2015) The RUSLE15 erosion assessment (JRC ESDAC), is based on a complex and diverse data model and is a good example land, and other factors. For such and similar reasons, some Slovenian experts are sceptical of the integration of large European databases. The main data on soil properties (soil texture, soil organic matter of EU erosion estimates. However, since no other comparable erosion data are available, the content, soil permeability and stoniness) were included in the LUCAS databases, soil structure in the Soil Map of ESDAC erosion estimates are published in some official EU documents and publications.

Europe (European Soil Database 1: 1 M), different uses or land use in Corine Land Cover 1: 100,000. Data from remote sensing (Copernicus) were integrated to determine vegetation and different statistics on agricultural crops, tillage type, crop residue management, etc. were used.

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Rf – Rainfall erosivity factor

Precipitation erosivity is the kinetic energy of the impact of raindrops on the ground and the magnitude of the associated surface water runoff. It is generally determined by (a) the intensity of the precipitation event [mm h-1], (b) the kinetic energy of the raindrops, their distribution, and the size and velocity of the precipitation, and (c) the duration of the precipitation event. The erosivity of precipitation is a key factor in erosion because it directly affects the separation of soil particles (the destruction of soil structural aggregates) and the washing away of soil particles.

The factor R [MJ mm ha-1 h-1 year-1] is the multi-year average erosivity index of precipitation, which measures the kinetic energy required to separate these particles from soil structure aggregates, as well as the intensity of precipitation. It describes the effects of precipitation and thus the frequency and abundance of sheet and rill erosion. Rainfall erosivity is calculated by multiplying the kinetic energy by the maximum rainfall intensity in 30 minutes of a daily rainfall event. Therefore, the RF gives the multi-year averages of the cumulative rainfall values of individual rainfall events. Rf can be credibly estimated if rainfall is accurately recorded at short intervals (1-60 minutes) over at least a few years.

In creating a map of soil erosion in Slovenia, we used data from the preliminary map of precipitation erosivity (Petan, 2010). The map was created based on measurements from 31 ARSO pluviographic monitoring stations with at least a 10-year record between 1999

and 2008, and supplemented with data from 13 ARSO precipitation stations with daily precipitation records.

Figure 4: R factor (Rf) map - rainfall erosivity of Slovenia (data source: Petan, 2010) The minimum Rf factor in Slovenia is 1.021, the average is about 3.390, and the maximum is The map shows the average amount, kinetic energy, and duration of precipitation represented as precipitation 14.369 MJ mm ha-1 h-1 year-1.

erosivity-a key factor leading to water erosion in all types of land use.

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Kf – Soil erodibility factor

Kf is the resistance factor of soil to water erosion, i.e. the erosion of topsoil and washing away of particles smaller than 2 mm with water. Erosion means the disintegration of the aggregates of the soil structure, which is usually accompanied by poor permeability of the soil, resulting in increased surface runoff and drifting of soil particles. Kf depends mainly on soil texture, soil structure, soil organic matter content, basic cations, and other soil properties that determine the cohesion and stability of soil structure aggregates and soil permeability. Kf [t ha h ha-1

MJ-1 mm-1] was measured on standard test fields (length 22.1 m, 9% slope) under standard conditions (bare soil, conventional tillage). Kf measurements are expensive and lengthy.

Erosion-resistant and low-erodibility soils have lower Kf values. These are clayey soils with greater cohesion (Kf ~ 0.007 - 0.020) and sandy soils that otherwise have lower cohesion but higher permeability (Kf ~ 0.007 - 0.026). Clay soils are moderately susceptible to erosion (Kf

~ 0.033 - 0.53). Soils with high silt content are most susceptible to erosion (Kf ~ > 0.053), harden quickly and have high surface runoff.

Since Kf is not systematically measured in Slovenia, we calculated Kf for the soil types of the Soil Map of Slovenia 1:25,000 (PK25) from the measured data of the corresponding representative soil profiles based on the average soil organic matter content (som), texture factor (tf), clay, sand, to a depth of 20 cm of the soil, soil structure class (ssc) and soil permeability class (sp).

Kf = [{2.1 x 10-4 tf1.14 (12 - som) + 3.25 (ssc - 2) + 2.5 (sp - 3)} / 100] * 0.1317

Figure 2: Soil erodibility (Kf) in Slovenia

(After Wischmeier and Smith (1978) and Renard et al. (1997)) The map of soil erodibility factor K shows the areas where the soil is more/less resistant to erosion. Higher soil erodibility is found in areas of Calcaric Cambisols of Goriška brda, Vipava valley, Slovenian Istria, Goričko, Kf was spatially defined within the boundaries of the PK25 soil mapping units.

Slovenske gorice, Kozjansko, on slightly leached Chromic, Luvic and Eutric Cambisols of Dolenjska and Bela krajina, and Dystric Cambisols of the hills of Škofja Loka, in the Pohorje mountains and partly in the Savinja valley and in the Koroška region.

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Cf – Land use and land cover factor

The C-factor (without unit) defines the impact of land use, land cover, and related agricultural practices on the (partial) reduction of soil erosion and the severity, frequency, and incidence of soil erosion processes. Cf is a quantitative indicator of the combined effects of land cover/

use and agricultural practices compared to reference conditions (land with bare soil, ploughed along the slope, value Cf = 1). The higher the value of the factor, the more pronounced the impact of erosion.

Cf is the most important factor in terms of possible measures to reduce erosion because it can be regulated by good agricultural practices and agricultural policies that influence the extent of erosion.

The most common arable crops from the “Requirements” data set (ARSKTRP, 2016-2019) were assigned Cf reference values from the literature. This was implemented for all land use types (MAFF, 2016-2019). Total Cf was combined from crop Cf (Cfplant) and land use Cf (Cflanduse) factors. Agricultural practices that contribute to erosion reduction were also considered and integrated.

The final Cf was calculated as the average Cf for 2016 - 2020.

Due to extensive forests, most of Slovenia has a low Cf with a value of 0.001. On agricultural Figure 3: Distribution of C-factor (Cf) of land use and land cover in Slovenia.

land, the lowest Cf values are achieved on grassland (0.049). On arable land, the Cf value varies The Cf map of the territory of Slovenia follows land use and established agricultural practices that contribute to the reduction of erosion. The values range from 0 to 0.38 with an average value of 0.039, with the lowest values found in greatly depending on the crop (e.g. from 0.123 in orchards to 0.225 in vineyards.

forested areas (Cf = 0.001), while larger and smaller areas with different agricultural use and higher values are clearly visible. For example, in Brda mainly permanent crops are cultivated, in Vipava valley and Slovenian Istria different types of agricultural use are interwoven, in Drava region, Ptujsko polje and Prekmurje medium Cf values dominate due to predominant use of arable land. In Slovenske gorice, the Cf value is also high due to the high proportion of vineyards.

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LSf – Relief factor

In RUSLE, the factors of slope length (Lf) and slope gradient (Sf) are usually combined into a factor LS, which represents the overall effect of topography on the degree of erosion (Van Remortel et al., 2004). Thus, the factor LS consists of the length of the slope (L), i.e., the distance from the starting point of surface flow to the point where the slope (S) decreases to such an extent that (a) deposition of eroded material begins or (b) flow begins to concentrate in surface channels (equation 19). Lf was calculated using the method presented by Desmet and Govers (1996).

Equation 2: Calculation of the LSf factor by Wischmeier and Smith (1978).

tan ß W

i

i

A = A

i

Σk tan ß W

j=1

j

j

where: λ = slope length (m); θ = slope steepness; m = (depends on the slope); 0,5: slope > 5 %; 0,4: slope between 3,5 % and 4,5 %; 0,3: slope between 1 % and 3 %; 0,2: slope < 1 %

The calculation of slope steepness (Sf) in each cell of the DMV grid plane for the study area was based on the algorithm of Zevenbergen and Thorne (1987): Equation 3: , where Gx= slope in direction x (m/m); Gy slope in direction y (m/m) G = G + G

2

2

i,j

x

x

Lf and Sf were combined in LSf with an algorithm according to Desmet and Govers (1996): S x ( λ -

m+1 λ )

m+1

j

j

j-1

LS =

j

( λ - λ ) (22,13)m

j j-1

Kjer je -L = faktor dolžine pobočja; Sj = faktor naklona pobočja za j-segment; λj = razdalja od spodnje meje j-segmenta do meje na vrhu hriba in m = eksponent dolžine faktorja Figure 4: The map of the LSf factor of Slovenia shows the hilly location of Slovenia.

USLE LS

The source of the LSf data is a digital elevation model with a resolution of 12.5 m: Green areas are flat areas and areas with gentle slopes, yellow are slopes with medium LSf (~ 2 - 5), and red are long and steep or very steep slopes Based on the above and other equations, we created a uniform grid layer of LSf with a with high LSf values (> 5). The map also shows areas with slopes > 26 ° (high mountains and steep slopes), where resolution of 10 m for the entire area of Slovenia (Figure 7).

LSf is not quite relevant.

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Pf – Factor of agricultural practice and tillage

Figure 8: Erosion in the vineyard area

The agricultural practises factor (Pf) was set to a default value of Pf = 1 in our RUSLE model (photo by Tomaž Poje).

because detailed data on terraces, boundaries, ploughing direction, etc., which correspond to Minimal erosion in a vineyard covered with grass

fragmented land use in Slovenia and would be suitable for nationwide soil erosion modelling, despite the slope. The only eroded areas are in the

are not available. Agricultural practises that protect soil from erosion are partially included ruts of the road.

in the Cf factor because some information is available on agricultural practices that reduce erosion (e.g., soil conservation treatments, winter cover crops, etc.).

Figure 9: Erosion on terraces

(photo by Borut Vrščaj).

Terraces effectively reduce the intensity and

consequences of erosion processes. Nevertheless,

it is necessary to ensure proper design of terraces,

prevention of erosion hotspots and consolidation

of terrace edges.

Figure 9: Severe erosion and a devastated crop in a field near Strehovci (photo by Tomaž Poje).

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Evaluation of soil erosion of agricultural land in Slovenia The high erosivity of precipitation strongly contributes to the fact that there are places with higher erosion rates in the west and northwest of Slovenia. High erosion is observed in the Goriška brda and, to a lesser extent, in the Posočje, due to the combination of tillage on gentle and steeper slopes and the high erodibility of some soil types. Highly erodible Calcaric and Eutric Cambisols are the cause of high erosion estimates in the Vipava Valley and Slovenian Istria. Terraces supported by stone walls are typical forms of the cultural landscape in this area. They are clear evidence that centuries ago, and in some places millennia ago, measures were taken to protect them from erosion. Since there were no sufficient spatial records of terraces in Slovenia, they are not included in the model. Therefore, we can conclude that soil water erosion in these areas is overestimated in our model. But the data on terraces exist, so the modeling should be updated.

In NE Slovenia, the Eutric Cambisols (silty and often poor in topsoil organic matter) are very susceptible to soil erosion. Despite lower precipitation, high levels of erosion are estimated, especially in vineyards and fields in Slovenske Gorice, Kozjansko and Goričko. In the plains (Dravsko Ptujsko polje, Prekmurje) there are very susceptible Dystric Cambisols in the valleys of Pesnica and Ščavnica moderately erodible Gleysoils. On these areas RUSLE-SI is not observed more severe erosion, which is otherwise common on the surrounding hills.

In Dolenjska, Notranjska, Karst and partly in Bela Krajina, Eutric and Chromic Cambisols develop mainly on hard limestones and dolomites. Higher clay contents and the presence of Ca are important factors for a good, stable polyhedral structure and sufficient water permeability throughout the profile. Stable and erosion-resistant terraces that are not supported by walls have been constructed Figure 10: Estimation of soil erosion in Slovenia using the RUSLE method.

over the centuries primarily to shape farmland on slopes rather than as erosion control measures.

The map shows the distribution of estimated erosion values in Slovenia. Goriška brda and Slovenian Istria stand out The extent of soil erosion on Rendzic Leptosols (the most common soil type in Slovenia) is due to land use (vineyards and olive groves), highly erodible soils and relief; ‘wreath’ of vineyards in Bela krajina, probably overestimated by the RUSLE-SI method. These soils are often characterized by high Vipava valley, Trška gora, Slovenske gorice, Haloze and individual slopes in NW Slovenia. According to RUSLE, forests have much lower or even marginal degree of erosion.

soil organic matter content, friable structure, and frequently thicker humus or even organic A The results of RUSLE erosion estimates on slopes > 50% are not meaningful enough, although they are marked on the horizons. Rendzic Leptosols occur on hard limestones and dolomites, which are predominant map. In addition to very steep slopes, there are also high mountains and lithosols (very thin skeletal soils, bare rocks).

on steeper slopes and at higher elevations in Slovenia.

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Soil erosion in Slovenia in figures

The RUSLE method reliably estimates erosion rates on reliefs with slopes less than 50% (< 26.6°). However, the estimate for higher slopes is less reliable. Therefore, estimates for a large portion of the Slovenian area (17.1%) with steep/steep slopes are less reliable, but still useful.

Broken down by groups of agricultural land use, erosion is calculated to be highest for permanent crops (17.79 t/ha on average), on land with intensive tillage, i.e. fields and gardens (7.58 t/ha), while total erosion on all grassland is somewhat lower (6.82 t/ha).

Calculations by type of agricultural use should show that erosion is most pronounced in uses with bare and cultivated soil. It is highest in olive groves (41.62 t/ha), vineyards (34.97 t/ha), much lower in intensive orchards (11.91 t/ha) and even lower in fields (7.64 t/ha). We assume that the RUSLE values for olive groves and vineyards, and to a lesser extent for intensive orchards, are exaggerated because a significant part of these land uses in Slovenia consists of terraces. Terraces were not included in the calculations because accurate data on selected terraced agricultural land in Slovenia were not known or available at the time of modelling. Repeated modelling that would consider data on terraces would significantly reduce erosion estimates for these areas.

For permanent grassland, erosion is estimated to be quite high (6.89 t/ha) given the permanent land cover, but this is understandable given the higher proportion of permanent pasture on (steep) slopes.

As expected, the estimate of the degree of erosion in forests is by far the lowest. Erosion in forests throughout Slovenia is estimated to be much higher (0.37 t/ha) than erosion in forests Figure 11: Erosion rates by selected categories of agricultural land use, by land use groups, and for the entire Slovenia.

on slopes < 50% and in the plain (0.25 t/ha).

Both field observations and calculations show that erosion is highest for permanent crops covering 2.62% of Slovenia’s land area, of which olive groves (0.12% of Slovenia’s land area) and vineyards (0.88%) are the most important. The The average annual erosion in Slovenia is estimated at 3.68 t/ha. For 82.9% of Slovenian land share of arable land (8.95%) and meadows (17.93% of the area) is significantly smaller. Depending on the climatic conditions (erosivity and amount of precipitation) and the different relief, forest cover (59.0%) contributes to the with slopes < 50% on slopes erosion is estimated at 3.13 t/ha. A relatively large proportion of relatively low erosion in Slovenia.

forests (59%) contributes to the low rating of the Slovenian erosion rate.

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Land use susceptible to erosion

Figure 12: Severe erosion in the field

In addition to rainfall (Rf), soil (Kf), and relief (LSf), the intensity of erosion is highly dependent on (photo by Tomaž Poje).

land use (Cf) and land management practises (Pf). The most sensitive types of agricultural land use Proper tillage can significantly limit erosion.

are vineyards, fields, and orchards. Less sensitive are grasslands and orchards. Even within the same Ploughing along the slope in this case contributed

significantly to severe erosion. Transverse ploughing, land use types, there are large differences due to cultivation practices or differences in land cover.

while not desirable on Planosols, would significantly limit the negative effects of the rain event.

Figure 13: Erosion in the vineyard

(photo by Tomaž Poje).

On the soil where the grass grows, there is almost no sign of erosion. On the other hand, there are signs of Figure 14: Severe erosion in arable land with high silt content in Prekmurje (photo by Geza Grabar).

severe erosion on the bare soil.

Lower humus content, texture (predominant silt) and treatment method resulted in severe erosion, runoff into watercourses and accumulation in the flatter part of the field.

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Adaptation and erosion control measures

The main guidelines for limiting erosion in the world are primarily related to land-use change, i.e., primarily preventing the conversion of forests to agricultural land and of grasslands to fields (FAO, 2019). In Slovenia, such guidelines are unlikely to be useful due to the (very) modest amount of agricultural land, low self-sufficiency and strategic security, high proportion of grassland, and especially the 59% forest area.

The second and third groups of erosion control measures should be introduced on a larger scale.

The second group includes protecting the soil surface, limiting the rate and amount of surface runoff (terraces, grazing, etc.), ensuring good soil absorption capacity and deeper and better soil permeability (tillage, avoiding soil compaction, etc.). The third group of measures focuses on improving the quality of surface soil horizons. Agrotechniques that increase humus content are important because they improve the shape and stability of soil structure aggregates and ensure adequate soil porosity. It is the conservation tillage adapted to the soil type, the sound soil fertilisation, the maintenance of an adequate soil acidity (liming) and a better condition of the soil biota. However, the most important measure is to ensure soil cover. This is especially important during summer storms and prolonged and heavy rains in spring and fall.

The RUSLE-SI method does not apply to wind erosion, which is becoming increasingly common. The bora wind in the Vipava Valley has significantly thinned the soil of bare fields and vineyards in winter in some places. According to farmers, wind erosion is also occurring more frequently in Prekmurje. In such areas, planting linear structures of trees and shrubs is a useful measure to protect against soil erosion while increasing biotic and landscape diversity.

Figure 15: Agricultural practices or measures on the same land use can well limit the occurrence / erosion - the case of the fields (photo by Tomaž Poje).

More attention must be paid to the good condition of agricultural soils and protection against erosion The picture shows a pronounced ~ 30-40 cm deep and in some places ~ 1 m wide erosion ditch formed on a field ploughed in autumn, but not sown / covered with overwintering crops. It is located between fields where in all its forms. The new programme period should focus on maintaining soil quality, preventing soi overwintering crops with similar slope and soil characteristics have successfully reduced erosion.

erosion, integrating erosion indicators, and promoting erosion control measures, among others.

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If we come to the conclusion

Erosion is very important, in some countries even the most important form of soil degradation.

Both visible erosion and erosion that is difficult to detect cause great economic damage that does not only affect the agricultural sector. By reducing the ecosystem services provided by soil, erosion causes broader environmental damage that affects everything from biodiversity to climate change.

Slovenia is vulnerable to erosion due to frequent heavy and intense rainfall (870 - 3600

mm/year) and a large proportion of steep topography. On the other hand, a fine-grained structure of agricultural land (average farm size 6.52 ha in 2016), 54.2% share of grassland in agricultural land and 59.0% forest cover suggest that erosion cannot be a serious problem.

Unfortunately, long-term and systematic measurements are not performed in Slovenia, so the estimates cannot be verified.

Nevertheless, we cannot ignore the fact that Slovenia has only a small amount of good agricultural land, that we are at the bottom of Europe in terms of the percentage of fields and gardens per capita (856.8 m2 / inhabitant in 2020), and that we are not self-sufficient in food supply.

It should also be noted that this brochure is mainly about erosion of agricultural land and less about other types of land use where erosion also occurs.

This confirms the consensus that soil must be protected from erosion in all types of land use, not just those where erosion occurs frequently. Agricultural production guidelines and policies in the agricultural development plan must adequately address the problem of erosion.

Figure 16 (left) and Figure 17 (right): gully erosion on cropland.

Reducing and preventing soil erosion is a fundamental element of soil conservation and These figures show the effects of advanced erosion that can occur on cropland after heavy rains. The left image shows a gully on soil with a silty texture on a gentle slope. The right image shows gully erosion on a flat field on environment protection, and thus sustainable agricultural production.

poorly permeable soils with unstable soil structure (photos by Tomaž Poje).

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Figure 19 (left) and Figure 20 (right): Consequences of erosion in permanent crops.

Both images show well the effect of advanced erosion that can occur when establishing or restoring permanent crops. In the olive grove of Slovenian Istria (photo Janez Bergant) there is a heavy downpour or longer intense rainfall deep eroded soils that were backfilled and unconsolidated; thus, in a very sensitive, erodible phase. In a Figure 18: Erosion in the olive grove after heavy rains (photo by Peter Kastelic).

felled vineyard in Vipava Valley (photo Borut Vrščaj) erosion is expected to accelerate at the site of the rut and due The Calcaric Cambisols of Slovenian Istria, Goriška brda, Kozjansko, Goričko and other parts of Slovenia are prone to to poor structure, compaction of the soil and non-maintenance. Both cases are very erodible eutric brown soils and erosion, especially when freshly ploughed, deeply tilled, backfilled or filled.

dictate preventive measures in the restoration / establishment of permanent crops.

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a

b

c

d

e

f

Photo: Geza Grabar (a), Janez Bergant (b), Tomaž Poje (c, d, f), REPUBLIKA SLOVENIJA

MINISTRSTVO ZA KMETIJSTVO,

GOZDARSTVO IN PREHRANO