Soil erosion is a physical phenomenon that involves the movement of soil particles by water or wind to other locations (to areas of so-called sedimentation, or deposition). The factors causing erosion can be divided into two groups: natural factors (surface topography, soil, precipitation, wind,) and human-dependent factors (land/soil use structure, type of vegetation, soil tillage system).
The intensity of soil degradation through erosion depends on the intensity and pattern of the individual factors. The environmental risks associated with erosion are not limited to the risk of the site and the soil itself. Eroded soil material is moved off-field and enters agricultural areas, including surface waters, contaminating them with soil particles and nitrogen, potassium and phosphorus compounds, as well as plant protection products. The result can be siltation of drainage ditches, roads and their shoulders, etc.
Erosion prevention strategies include:
- proper organisation of land use, i.e. according to their habitat potential and exposure to degradation, management of set-aside and fallow land to prevent their further degradation,
- using cultivation techniques and systems that improve soil structure and retention, cultivating row crops across the slope, reducing soil movement and mixing, counteracting compaction by choosing the right equipment and tyres,
- maintaining a positive organic matter balance,
- selection of crops in rotation with a strong, taproot system,
- maintenance or reconstruction of protective elements in the form of baulks, terraces, trees, shrubs and ponds,
- maintenance and establishment of tree and shrub strips,
- construction of multifunctional small retention reservoirs on valley bottoms with permanent or temporary water flow.
The basic anti-erosion treatments are:
- the spatial arrangement of productive and protective uses according to the relief of the terrain, taking into account rainwater run-off paths,
- transverse tillage,
- use of anti-erosion agrotechnics (no-till, mulching), exclusion of ploughing on steeply sloping land,
- planning of agricultural transport routes taking into account the relief of the terrain, reinforcement of road sections prone to erosion,
- reclamation and management of erosion wastelands (e.g. ravines, steep slopes),
- crop rotations / anti-erosion rotations with plants that protect the soil from surface scouring and gouging (e.g. strong-rooted fabaceous plants and their mixtures with grasses), winter cereals instead of spring cereals,
- the use of undersown, intercropping and catch crops, leaving post-harvest residues on the surface to keep the soil under cover for as long as possible,
- an earlier sowing date for winter crops, for better plant tillering before the winter period,
- backfilling/removal of small erosion forms where periodic surface water runoff is concentrated.
6.10.1 Soil cultivation
The soil tillage system has a significant impact on the possibility of soil erosion. This applies to both organisational and technical matters. Of the organisational matters, the greatest influence on the risk of erosion comes from:
- increasing the area of fields, eliminating baulks, blockages and other surfaces that can hinder the erosion process,
- removal of trees and hedges, which provide natural protection against wind erosion and soil drying out,
- removal of terraced farmland, often linked to its expansion,
- the allocation to cultivation of land that should remain wooded, e.g. due to soil type or the degree of slope,
- practising monoculture leading to the destruction of soil structure and increased soil waterlogging,
- the abandonment of mid-crops, intercrops and catch crops in simplified low-cost rotations, leading to a reduction in the length of time the crops are covered on the soil,
- overgrazing, especially in hilly areas,
- cultivation work carried out with inappropriate soil condition, leading to the destruction of soil aggregates, soil fragmentation and deterioration of rainwater soaking,
Technical errors leading to soil erosion are:
- cultivation of light and very light soils with active machinery,
- ploughing along the course of the slopes of the land to facilitate the run-off of water with the soil,
- sowing winter crops too late,
- kneading, especially of wet soil, by heavy machinery.
- The last mentioned error, due to its importance, is described in more detail later in the lesson.
6.10.2 Soil compaction
In addition to its yield-forming role, soil is also a place where agricultural machinery moves. Soil compaction is generally the result of its mechanical compaction by heavy equipment or when grazing animals, especially under conditions of excessive moisture. Technological progress has increased the weight of the machinery used and the pressure of the tyres on the soil surface. Narrow tyres and heavily loaded axles are particularly dangerous. The moisture content of the soil and the weight of the machinery used play a major role in increasing the risk of overloading the soil. Excessive cultivation of wet soils has the effect of compacting the soil and destroying the soil spaces that supply oxygen and carry away carbon dioxide. This results in lower soil temperatures and poorer plant growth. Wide radial tyres and the skilful adjustment of the pressure in them – depending on the condition of the soil – is of great importance in reducing soil compaction by increasing the contact surface.
Compaction can involve surface soil layers, or subsoil compaction. Superficial compaction can be removed fairly easily by soil loosening treatments (ploughing, cultivation, etc.) and does not pose a threat to soil quality or, in the long term, to yield levels. Subsoil compaction is significantly more difficult and costly to eliminate, e.g. by deepening.
Soil compaction must be monitored and removed as quickly as possible as it is very important for agricultural production.
Excessive compaction of the soil and subsoil affects important soil functions by reducing pore volume and pore continuity, and thus the ability of the soil to transmit water and air. Lower water conductivity results in poorer water retention and consequently surface runoff and water erosion. Poor soil oxygenation leads to reduced plant growth, a shift in soil biology in the undesirable direction of anaerobic transformation and, as a result, increased soil nitrogen loss (denitrification). Subsoil compaction significantly restricts root development and root penetration into deeper soil layers, with a consequent reduction in the size and quality of crop yields. It also has a detrimental effect on soil macro-organisms, which lose the ability to move through the soil. Soil or subsoil compaction significantly reduces the quality of the soil, causes yield loss and impairs the effectiveness of fertilisation and crop protection, making it unsustainable to produce on it.
Simple methods can be used to check the presence and depth of soil compaction on an ongoing basis. This test can be carried out by driving a thin, smooth, sharpened rod by hand; a distinct resistance will be felt at the depth of the soil compaction zone. Alternatively, a specialised tool – a penetrometer – can be used, which gives the depth and force value when driving into the soil, giving it in Pascals.
Counteracting soil compaction is founded on:
- proper use of mechanical equipment (reduced tyre pressure, twin wheels, tracked equipment, reducing the number of passes, avoiding working on wet soil),
- improving soil resistance to compaction (e.g. improving soil structure and no-till). An appropriate response to the presence of soil compaction is the use of appropriate tillage, as well as the sowing of plants with a strong, taproot system (so-called phytomelioration plants, such as rape, faba bean and others), creating passages for water through the compacted soil layer.