Soil erosion is the excessive erosion of soils , caused by improper human land use , e.g. removal of protective vegetation through overgrazing or deforestation , as well as fallow periods that are too short . The loss of the topsoil , i.e. the most fertile and agriculturally most important part of the soil , is particularly problematic .
Persistent soil erosion initially leads to a deterioration in the quality of the soil ( soil degradation ). Since 1945, the area affected by soil degradation has totaled more than 1.2 billion hectares worldwide - this corresponds to the land area shared by China and India.
The degradation can ultimately lead to the complete loss of the agricultural usability of the soil (soil evastation). It is estimated that the loss of topsoil through erosion worldwide amounts to around 23 to 26 billion tons per year (on average 14 to 16 tons per hectare per year). This corresponds to an annual loss of less than one percent of the arable land.
Soil erosion is a problem with far-reaching ecological, economic and social consequences. Therefore, various soil protection measures have been introduced around the world , which, however, have not yet completely eliminated the problem. The United States Department of Agriculture estimates that, despite the measures that have now been taken in the USA against soil erosion, millions of tons of fertile soil are washed away from farmers' fields in the Mississippi catchment into the Gulf of Mexico every year .
Soil erosion occurs mainly through runoff rainwater or through wind.
- Linear erosion by water (groove erosion)
This is caused by rainwater flowing off in short-lived rivulets. Where this water collects and flows together, the concentrated runoff creates gullies , and in the case of particularly strong runoff, real gorges in the terrain. This can lead to retrograde erosion, in which a particularly steep slope or a depth line moves up the slope as erosion progresses.
- Extensive erosion by water ( denudation )
In the case of particularly heavy rainfall, on a slope free of vegetation, rainwater can actually flow off over a short period of time and wash away the soil. In most cases, however, the surface erosion occurs through the interplay of small-scale linear erosion. In this way, the ground is lowered more or less evenly, unnoticed.
Heavy raindrops that hit the ground directly also play an indirect role in the washing away of the ground, as the high kinetic energy causes the fine soil constituents, which are moved over very short distances (centimeters), to clog larger pores and reduce the soil's ability to absorb water overall and thus its susceptibility to erosion increase ( siltation ).
The soil carried away by the rainwater is either flushed with the water into a nearby body of water or further down the slope, where the slope and thus the flow speed of the water decrease, deposited as an alluvial fan .
- Wind erosion ( deflation )
Wind erosion occurs mostly on light soils. With this form of erosion, the wind blows away the uppermost, relatively fine-grained soil layers. These are deposited again elsewhere.
- Tunnel erosion
- Long-lasting, frequent and heavy rainfall (water erosion). They create eroding runoffs on the soil surface
- Water-rich snow cover that melts quickly (snow erosion)
- Storms with high wind speeds (wind erosion)
- Substrate and soil properties
- which promote the erosion processes. As susceptible to erosion is then referred to soils if they have the following characteristics:
- Small pore volumes for preferential flow
- Tendency to surface compaction and poor stability of the soil
- low infiltration capacities
- The soil type influences the erosiveness of the soil. So have sandy and silty soils increased susceptibility to erosion on
- The relief has an effect on the speed and amount of the draining water:
- The greater the slope, the faster the water flows off and the erosion effect is stronger
- The amount of runoff increases on long slopes and on surface shapes where water collects on multiple slopes.
- The degree of land cover
- by vegetation or mulch determines how much surface erosive rain is exposed:
- The lower the land cover, the greater the erosiveness. The protection against rain erosion is based on the effect that water droplets are slowed down by the impact on the ground-covering layer and thus have less kinetic energy when they hit the ground. A high degree of ground cover also slows the wind directly above the ground surface and thus reduces wind erosion.
- The type of land cover influences the erosiveness depending on the height of the vegetation. For example, corn plants slow down impacting drops, but they fall relatively far from the tall plant to the ground and thus develop a high speed again. For optimal protection against erosion, the soil should be covered immediately above the surface.
- The rooting with plant roots of the naturally occurring and adapted plants ( prairie grass ) at the respective locations stabilizes the soil in an optimal way physically and reduces the eroding effects of wind, rain and surface runoff. Other plants with poorer root penetration, such as Phedimus stoloniferus , also have poorer soil stabilizing properties.
- In particular, land use in the tropics requires a sufficiently long fallow period for the cultivated areas due to the extreme heavy rainfalls and thin soil . If an area that has been cleared by fire is traditionally used for one to two years and then lies fallow for 20 to 25 years, the soil can regenerate itself even after erosion has started. However, increasing intensification through population growth leads to a shortening of fallow land and increasing soil erosion.
Arable use on slopes without any soil removal is not possible. A realistic goal can only be to limit soil erosion to a tolerable level. On very deep soils, soil erosion of a maximum of 10 t / ha per year (corresponding to a layer thickness of around 0.6 mm) is considered to be tolerable today. In view of the slow formation of new soil due to weathering processes, however, this value should generally be significantly lower.
Promotion of soil tilling and mulch management
In order to curb erosion on arable land, it is primarily necessary to ensure that rainwater does not collect on the surface of the soil and run off on the surface. This can be achieved by two types of measures:
- Promotion of the soil : humus supply, liming, careful soil cultivation , sufficient rooting and the avoidance of soil compaction and encrustation promote the water absorption capacity of the soil . At the same time, they reduce the risk of erosion. In waterlogged soils, the regulation of the water balance (often through drainage ) has a similar erosion-reducing effect.
- Mulch management: The most important measure to protect against soil erosion is to leave plant residues on the soil surface ( mulch ). A mulch cover breaks the impact force of the raindrops, increases water infiltration into the subsoil and thus reduces surface runoff.
The sowing in a mulch layer can be used for almost all crops. It is possible after basic tillage with and without a plow. Find cover crop for mulch preparation use, these are mostly for summer furrow ordered. The catch crop, carefully tilled after plowing, leads not only to erosion protection, but also to a reduction in nitrate discharge and stabilization of the soil structure . In favorable locations, row crops can be sown in spring without additional seedbed preparation ( mulch sowing without seedbed preparation). The method of mulch sowing with seedbed preparation is to be used when soils warm up slowly and dry out with a delay. In dry locations, the emergence of the summer catch crop is at risk if there is no rainfall. Under such site conditions, tillage without plowing with plant residues of the previous crop left on the surface or mulched in flat is a way of reducing erosion.
The following catch crops have proven their worth for mulching:
- Mustard (nematode-resistant varieties in sugar beet cultivation) is a less demanding species that freezes off safely. If sown in good time (at the end of August), it forms sufficient shoot mass for good soil cover.
- Phacelia requires a fine crumbly seedbed and earlier sowing. Placing the main fruit in the phacelia mulch is not very difficult because of the low coverage.
- Grasses (especially German ryegrass and winter turnip rape ) come into consideration as overwintering species . Before sowing the main crop, the cover crop should usually be killed by chemical treatment.
A special form of mulch cultivation is no-till farming , i.e. no-till farming . This means that the seeds are sown without tillage directly after the harvest or in the uncultivated fallow land . This form of agriculture is increasingly practiced in North America in particular. The residues of the plant material from the preculture remain as mulch on the field. Special seed drills only open narrow slots in the soil surface, which are covered with soil again after the seed has been placed. The soil only experiences mechanical interference in the actual seed rows. Various studies in the USA have shown a sometimes drastic decline in soil erosion that results from completely abandoning the plowing of arable land. For example, soil erosion fell by 75 percent on corn fields in the US state of Indiana , and by 90 percent on tobacco-growing areas in Tennessee . However, the amount of soil erosion reduction depends on the respective soil and the crops grown. However, no-till does not only have advantages and this method still needs some improvements. At least in the first time after the conversion from conventional agriculture to no-till, increased use of pesticides is necessary for various reasons .
Cultivation across the slope
In order to prevent water from flowing down the slope, cultivation should take place across the slope, ideally parallel to the contour line. This avoids the erosion-promoting lanes in the direction of the slope. If the field boundaries are redrawn as part of the land reorganization and the road and waterway network expanded, the fields should be laid out in such a way that cross-management can take place. Old arable terraces , vines and hedges are to be preserved as far as possible.
Shortening of the erosive slope length
By shortening the slope length, the flow path and thus the transport capacity of the surface water is restricted. A simple step is to subdivide a large area into two parts across the slope, which are cultivated alternately with winter and summer crops. The criterion of slope length is closely related to the question of the acceptable field size. The given location conditions and the existing structural elements essentially provide the framework. The merging of fields required by economic and technical constraints is only to be approved if the tolerable soil erosion is not exceeded as a result.
Protection against wind erosion
Wind erosion risk are mainly sandy, humus-rich soils, especially used for farming peat soils . The most effective protection against erosion is an evergreen plant cover. Where this is not possible, the soil must be protected from soil erosion by means of windbreaks ( hedges ). It depends on the correct structure and spacing of the protective strips. Wind protection systems not only serve to protect against erosion, they also create a growth-friendly microclimate at the same time . They reduce unproductive evaporation and offer animals and plants protection and a habitat.
In Germany, the Federal Soil Protection and Contaminated Sites Ordinance (BBodSchV), last amendment of July 31, 2009, §§ 7 and 8, in the state of Baden-Württemberg by the Ministry for Rural Areas, Food and Consumer Protection with the ordinance on the classification of agricultural Areas according to the degree of erosion risk (Erosion Protection Ordinance - ErosionsSchV) of May 29, 2010 created the legal basis for the creation and publication of cadastre for erosion risk.
Soil erosion in Europe
- In north and north-west Europe, soil erosion is comparatively low, because the rain falls on mostly gentle slopes and is evenly distributed over the whole year. As a result, the area affected by erosion is quite small. In the Scandinavian countries of Norway, Sweden, Finland and Denmark, water erosion is considered to be the main problem, particularly because of its significant contribution to phosphorus pollution in water bodies. In Iceland, the erosion rates are significantly higher due to the harsher climate, which is why a soil protection authority ( Landgræðsla ríkisins ) was founded there as early as 1907 .
- In the Mediterranean region , prolonged dry periods are often followed by heavy rainfall, which can cause considerable erosion damage, especially on relatively steep slopes. Here, the leaching of clay particles and thus the "cementing substance" between larger soil particles has high sodium concentrations in the soil (a measure among other anthropogenic soil salinity ) favors, which increases significantly the erosive effect of heavy rainfall on soil. The same applies to regions with a comparable climate in other regions of the world.
The potential social consequences of soil erosion and the associated loss of fertile soils are illustrated by the migration movements that took place in the USA in the 1930s during the Dust Bowl and in the African Sahel zone in the 1970s and are currently taking place in the Amazon basin. The Dust Bowl states in the American Midwest take their name from major wind erosion events and the associated dust storms of the 1930s. As a result of the Dust Bowl, tens of thousands of farmers had to give up their businesses. In search of work, some of them moved as far as California , where they were housed in reception camps and exposed to exploitation and starvation. Nobel laureate in literature John Steinbeck addressed her suffering in the novel The Fruits of Wrath , which was awarded the Pulitzer Prize in 1940 . The Soil Conservation Service , the state-owned soil protection organization in the USA, was founded in response to this event and thus laid the foundation for erosion research. Based on their planning, the Great Plains Shelterbelt was created from 1935 , a 100 miles wide belt of trees from the northern to the southern border of the USA as protection against wind and excessive evaporation.
However, long before that, people repeatedly caused soil erosion through improper land use, with often serious consequences:
- Extensive erosion after the deforestation of the forests on the hills around Athens was endangered as early as 590 BC. The supply of the city with food, so that the statesman Solon suggested that the plowing of steep slopes be forbidden. At the time of the Peloponnesian War (431-404 BC) a third to three quarters of the food consumed in the cities of the Greek homeland came from Egypt or Sicily.
- In Latium in ancient Italy, deforestation and intensive agriculture on the hills of the Campagna Romana contributed to the fact that the Pontine Plain , which had been highly productive in agriculture up to that point, around 200 BC. . Had turned into a swamp AD, located in the malaria -transmitting Anopheles mosquito spread strong.
- The city of Antioch was one of the largest and richest cities in Roman- occupied Syria and there were hundreds of villages and small towns around it. In the 1970s only seven villages were still inhabited. Until they were uncovered, the ruins of Antioch were buried under up to 8 meters of soil that had previously been eroded further north in the highlands. The doorsteps of ancient ruins in these highlands are now one to two meters above bare rock, which shows how much soil must have been lost there.
- In the course of the so-called Magdalene flood in July 1342, Central Europe experienced historically unique high soil erosion rates. As a result of extremely heavy rainfall due to Vb weather conditions and a correspondingly extremely high surface runoff (estimated to be up to 50 to 100 times more than during the rainfall that led to the flood of the Oder in 1997 ), according to calculations, 13 billion fell in Germany during this event Tons of arable land was washed away in higher areas and the surface of the arable land in the affected areas was lowered by an average of 5 centimeters in a few days. Whole regions became uninhabitable due to the resulting canyon systems. These gorges can still be identified in the landscape today. In addition to the heavy rain in July 1342, the cause of this catastrophe is believed to be the strong spring floods of that year and periods of low rainfall in early summer, which made the soil particularly prone to erosion. In addition, it was only the conversion of forest to arable land, which had been carried out in Central Europe for centuries in the run-up, made possible such an effective attack on erosion over such a large area. Due to other extreme weather events, the soil surface of the agricultural areas was lowered by an average of 10 centimeters in the 14th century.
- General soil erosion equation
- Soil protection
- China's Green Wall
- Hans-Rudolf Bork, Helga Bork, Claus Dalchow: Landscape development in Central Europe. Effects of humans on landscapes . Klett-Perthes, Gotha et al. 1998, ISBN 3-623-00849-4 .
- Markus Fuchs, Andreas Lang, Joseph Maran : Reconstruction of an ancient landscape. In: Spectrum of Science . November 2000, pp. 85-87.
- Hartmut readers : landscape ecology. Approach, models, methodology, application (= UTB for science. Uni pocket books. Geography, land care, ecology, environmental research 521). 4th, revised edition. Ulmer, Stuttgart 1997, ISBN 3-8252-0521-5 .
- Christiane Martin, Manfred Eiblmaier (Ed.): Lexicon of Geosciences. In six volumes. Spektrum, Akademischer Verlag, Heidelberg et al. 2000–2002.
- David R. Montgomery : Dirt - The Erosion of Civilizations . Second edition. University of California Press, Berkeley (CA) 2012, ISBN 978-0-520-27290-3 .
- Gerold Richter (Ed.): Soil erosion. Analysis and assessment of an environmental problem. Scientific Book Society, Darmstadt 1998, ISBN 3-534-12574-6 .
- Soil pollution: erosion on the website of the Federal Environment Agency (UBA)
- Soil erosion - endangerment of the resource soil on the website of the Federal Institute for Geosciences and Raw Materials (BGR)
- The Soil Erosion Site (English)
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), p. 174.
- Christoffel den Biggelaar, Rattan Lal, Keith Wiebe, Vince Breneman: The Global Impact of Soil Erosion on Productivity. I: Absolute and Relative Erosion-Induced Yield Losses. Advances in Agronomy. Vol. 81, 2004, pp. 1-48, doi : 10.1016 / S0065-2113 (03) 81001-5
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), foreword.
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), p. 2 ff.
- Franz Rothe: Cultural-historical and cultural-ecological basics of the intensification and irrigation techniques of traditional agricultural cultures in East Africa: their development background and their ability to survive. Philosophical Faculty of the Albert Ludwig University of Freiburg i. Br., 2004.
- Rolf Derpsch: Sustainability (as of April 14, 2014). No-till sowing: sustainable agriculture in the new millennium.
- David R. Montgomery: Dirt - The Erosion of Civilizations. 2012 (see literature ), p. 211 f.
- Landwirtschaft-bw.info: Justification of the Erosion Protection Ordinance (October 9, 2010)
- Landwirtschaft-bw.info: Erosion register , with additional links (October 9, 2010)
- Ása L. Aradóttir: Restoration challenges and strategies in Iceland. Landgræðsla ríkisins, Hella 2003 ( PDF 321 kB)
- Karl-Erich Schmittner, Pierre Giresse: The impact of atmospheric sodium on erodibility of clay in a coastal Mediterranean region. In: Environmental Geology. Vol. 37, No. 3, 1999, doi : 10.1007 / s002540050377 . , pp. 195-206,
- H. Ghadiri, J. Hussein, E. Dordipour, C. Rose: The effect of soil salinity and sodicity on soil erodibility, sediment transport and downstream water quality. In SR Raine, JW Biggs, MN Menzies, DM Freebairn, PE Tolmie (Eds.): Conserving Soil and Water for Society: Sharing Solutions. Proceedings of the 13 th International Soil Conservation Organization Conference - Brisbane, July 2004. Australian Society of Soil Science Incorporated / International Erosion Control Association (Australasia), 2004, Paper No. 631 ( PDF 356 kB)
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), p. 50.
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), p. 58.
- David R. Montgomery: Dirt - The Erosion of Civilizations . 2012 (see literature ), p. 71.
- Entire paragraph after Hans-Rudolf Bork, Hans-Peter Piorr: Integrated concepts for the protection and sustainable development of Central European landscapes - opportunities and risks, illustrated using the example of soil and water protection. P. 69–83 in: Karl-Heinz Erdmann, Thomas J. Mager (Ed.): Innovative approaches to protecting nature. Visions for the future. Springer, 2000, ISBN 978-3-642-63075-0