Soil loss – any soil crumb counts

In principle, both soil loss by water and wind erosion are natural land forming processes triggered by factors such as precipitation, wind, slope and soil type (see also UBA topic pages "Soil loss by water" and "Soil loss by wind"). The risk for soils from soil loss, taking only the natural influencing factors into account, is referred as the potential soil loss risk. The main natural influencing factors are the soil conditions, site-specific characteristics and climatic conditions. However, it can be assumed that soil loss does not occur to any significant degree when naturally formed year-round plant cover is present. The currently observable dimension of soil loss in Central Europe is a result of human activities, mainly food production. In combination with the natural factors, usage dependent influences determine the actual soil loss risk.

The most important usage dependent factors are the structure of the landscape, the cultivated crop type or crop type rotation, and soil tillage.  

• Large open cultivated areas without small-scaled structures (hedges, green strips, rows of trees, etc.) favor erosive processes.
• Crops that develop late in the year or are planted in wide row spacing (such as maize, sugar beets) leave most of the soil uncovered, especially in winter, spring and early summer. Wind and water can directly attack and erode the soil. Without accompanying measures such as intercropping, undersowing or mulching, these crops face a significantly increased risk of soil loss.
• The intensity of soil tillage influences both the soil cover in terms of incorporation of crop residues and the soil stability. Conservation tillage practices support both soil cover and soil stability and thus, for example, the ability of soils to absorb and store water. The risk of soil loss is reduced.

In addition, climate change increases the risk of soil loss significantly. In particular, the increasing probability of dry phases, local heavy rainfall and the possibility of increasing wind speeds are decisive. This development emphasizes the need to protect our soils even more strongly in the future from soil losses and the associated degradation.

Due to the natural and climatic conditions in Germany, soil loss by water is dominant in the predominantly hilly landscapes, whereas especially in the flatter terrain of northern Germany and near the coast, wind is the predominant trigger of soil loss, also due to the sandy soils in this area.

The direct consequence of soil loss on the affected areas (on-site) is a reduction in soil thickness in the medium to long term (Figure 1). In the process, nutrient-rich, humus-rich topsoil is lost, especially on hilltops or upper slopes, which is important for securing agricultural yields. This loss effects natural soil functions such as water and nutrient holding capacity and the ability to filter and break down pollutants. This threatens our food security in the long term, as fertile soil is lost faster than new soil can be created. Soil develops very slowly. It takes more than 100 years to form one centimeter of humus-rich soil that can be lost in a single erosion event during a heavy rain. Since the beginning of human agricultural activity, soil losses of several decimeters are not uncommon in many places.

Moreover, the soil material transported by water or wind can damage neighboring cropland as well as terrestrial and aquatic ecosystems and infrastructures (off-site) by deposition:

• On depositional areas, silting and the covering of plants can reduce crop yields.
• The nutrients and pollutants bound to the soil particles can contribute to pollutant enrichment and eutrophication or acidification in neighboring terrestrial and aquatic ecosystems. In particularly sensitive water bodies, the goals of the EU Water Framework Directive are not being achieved (see also the UBA topic page: "Water Framework Directive").
• The deposited soil material can cause considerable damage to anthropogenic infrastructures such as settlement and traffic areas, sewage systems and dams.

In order to ensure long term food security, it needs to be the goal of all stakeholders (federal government, states, agriculture and water management) to protect our soils against degradation and thus also against soil loss. Therefore, the actual soil loss risk needs to be assessed, soil loss events need to be recorded and soil loss-reducing measures need to be taken. In this way, agricultural land can be protected from the damage caused by soil loss both on site and off-site. In addition, neighboring sensitive ecosystems (land, water bodies) but also infrastructures are protected from material and pollutant input.

Figure 1: Reduction of soil depth caused by continued soil denudation.

Source: FG II 2.7 / Umweltbundesamt

Soil loss occurs irregularly and spatially limited. This makes it challenging to observe, document, balance and evaluate the effects of the process. Soil loss is either not very visible and creeping, associated with extensive soil loss, or it occurs, for example, caused by heavy rain, clearly visible, measurable and mappable in linear form as rills (two to ten centimeters), gullies (ten to 40 centimeters) up to ditches (larger than 40 centimeters) (Figures).

Soil loss by water

Source: S. Marahrens / Umweltbundesamt

Soil loss by wind

Source: Frank Glante / Umweltbundesamt

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In order to determine locally the actual soil loss caused by water or wind, it is necessary to record single events. The most appropriate method is a standardized mapping. Both on-site and off-site erosion forms should be recorded and documented. For a German-wide harmonized standardized recording, filed mapping instructions are available as working aids for soil protection law enforcement for both soil loss by water (DWA 2021) and wind (LABO 2018). However, mapping involves considerable effort and is currently only possible on a random basis.

For the regional and supra-regional observation, among other things for the designation of soil loss hazards by water and wind, models or corresponding methodological approaches are used. They are applied at the level of the German federal states, as one basis for enforcement, and German-wide for the supra-regional evaluation of soil condition. On the national level, the methodological approach according to DIN 19706:2013-02 was used for the assessment of soil loss risk by wind (see also UBA topic page "Soil loss by wind erosion") and by water the Universal Soil Loss Equation (USLE) (see also UBA topic page "Soil loss by water erosion").

Figure 3: Linear soil loss forms are very diverse and easy to capture

Source: V. Prashun / ART

The German Federal Soil Protection Act (BBodSchG) and the German Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV) provide a nationwide framework for soil protection requirements. Among other things, these regulations contain requirements for the protection of soils against and the prevention of soil loss. With regard to the management-related factors, the BBodSchG (Part Four "Agricultural Soil Use") provides the guideline with the principles of so called "good agricultural practice (GAP)" in § 17 and obliges agriculture to take precautions and to avoid soil loss. This addresses the need for site-adapted management and the preservation of natural structural elements of the field to prevent unsustainable soil loss as a precaution. A prerequisite for the implementation of site-adapted management is the assessment of the soil loss risk on the areas concerned. This assessment, including the necessary measures, can either be determined by a farmer himself or, if required, obtained through appropriate consultation in accordance with § 17 BBodSchG. In many of the German federal states, procedures exist for this purpose.

In the BBodSchV part six § 9 supplementary regulations for the hazard prevention of soil degradation due to soil loss by water are fixed.

In Germany the implementation and control of the federal requirements, i.e. the transfer into agricultural practice, is the responsibility of the federal states. However, it is apparent at this interface that there are deficiencies in the existing federal legislation. One deficit that has an impact on enforcement is that the principles of the so called “good agricultural practice (GAP)" have not yet been further specified or underpinned with binding standards. This makes it impossible to monitor compliance with the principles. Furthermore, there is no provision for monitoring compliance with the precautionary recommendations in enforcement. Thus, although the protection against soil loss is legally demanded, the enforcement of precautionary measures in the field of agricultural land use is not provided for in the existing instruments of soil protection law.

Furthermore, in the area of EU direct payments to farms, the regulations of the Agricultural Payments Obligations Ordinance (AgrarZahlVerpflV) must be observed. It regulates nationally the granting of subsidies of the Common EU Agricultural Policy (CAP) within the framework of the cross-compliance (CC) provisions. Depending on the risk to a farm's land, for example, the payment of subsidies is tied to certain requirements for the prevention of soil loss. In principle, the instrument is suitable for promoting precautionary measures. At present, however, the conditions only represent a minimum standard, since the generally available state of the art in "good professional practice" according to § 17 BBodSchG guarantees more effective precautions. Moreover, compliance with the requirements is voluntary and detached from the Federal Soil Protection Act, the principles of which are mandatory.

Suitable soil cultivation techniques and a large number of recommendations make an important contribution to protecting the soil from soil loss.

Effective agricultural management measures are known and extensively described, among others published by the Federal Ministry of Food and Agriculture (BMEL 2015, BMEL 2016). Management practices to increase the degree of soil cover by plants and plant residues are important. Here, the German Federal Ministry of Food and Agriculture (BMEL) states a rule of thumb of at least 30 percent soil cover all year round, which should be given. To maintain the aggregate stability of the soils, conservation farming methods should be used. This should be accompanied by supporting measures to increase structural diversity in the agricultural landscape (land development and land readjustment).