Salinization
In soil science, salinisation refers to an excessive accumulation of water-soluble salts. The processes by which salts accumulate in the upper soil layer , the characteristics and the causes are examined . Along with acidification, salinization is one of two possible long-term results of soil development. Salinization occurs when the soil has a negative water balance , i.e. the evaporation in six to nine months of a year is greater than the precipitation . In addition to the natural development of a soil, salinization can be accelerated considerably by human activity .
Strictly speaking, a distinction must be made between salinisation, the accumulation of easily soluble salts and alkalisation , the accumulation of sodium hydrogen carbonate and sodium carbonate with a simultaneous increase in the pH value . A special case of salinization is sodification , in which primarily sodium chloride ( table salt) accumulates in the surface.
The origin of the salts involved is also important. They can come from the earth's atmosphere (atmogenic salts). In these cases one also speaks of "day water salinization". The salts can also be transported into the upper soil layers by rising groundwater . This is called “groundwater salinization”, which can also occur, for example, in coastal regions of the humid zones, for example through excessive abstraction of groundwater, through which seawater can penetrate the groundwater body. Weathering minerals can release salts into the environment, and fossil salts (marine sediment) can be a source. In addition to these natural sources, artificial irrigation and fertilizers can also be considered.
Physical process
The physical process is often very similar. The high level of evaporation on the surface means that salts dissolved in water accumulate on the surface. Since no water drains off, the salts remain in the upper soil layer. The effect increases with artificial irrigation, as more water is now available to transport the salts. Additional salt load through the use of groundwater further intensifies the effect. A salt crust forms on the surface.
Importance of salinization
Salinization affects 20% of the agricultural land and 50% of all irrigated areas and is the second largest soil protection problem .
In Syria alone , 30 to 35 percent of the arable land has been lost to salinization. In Egypt it is 30 to 40 percent, in Pakistan less than 40 percent, in Iraq 50 percent and in the United States 20 to 25 percent. In part, this goes back to the irrigation technique of the Sumerians in Mesopotamia . This can only be counteracted through drip irrigation and drainage systems. As a medium-term countermeasure, in the history of many cultivation areas there has also been a clear demonstrable change in the plant species cultivated, for example from wheat to more salt-resistant barley .
Salinisation also occurs in rice cultivation . In the dry season , the rice fields continue to be irrigated, so that the salinity of the standing water in which the rice grows increases due to the strong evaporation.
In the bank areas of receding waters such as the Aral Sea or the Dead Sea , massive salt incrustations can occur. There are plants ( halophytes ) that are adapted to salty soils, but cannot be used for agriculture.
Antidote
The best way to use saline areas again is to irrigate large areas and drain the water through drains before the sun has dried the solution. This “rinsing” usually has to be carried out several times.
Salinisation can also be counteracted by incorporating special substrate mixtures. The functional principle of this technology is to introduce superabsorbents in such a way that there is no gel formation , which the water denies the roots. It is also intended to prevent rainwater from simply being washed away. The aim is to make water as far as possible and directly accessible to the absorbers in the roots. As a result, the amount and frequency of irrigation can be greatly reduced, thus reducing the risk of salinization. The substrates can also be combined with fertilizing properties .
Effects of salinization on agriculture
The high salt concentration in the soil disrupts the osmotic processes that plants use to absorb water and nutrients. At the same time, sodium , chlorine and boron ions accumulate in the plants, which at the same time lack potassium and calcium . The soil compaction associated with salinization makes it difficult for the roots to grow. These effects are accompanied by a deterioration in the metabolism of the soil organisms.
Different arable crops are affected by salinization to different degrees. Barley is considered to be the most salt-resistant grain, and sugar beets are also relatively resistant. Pineapples , apricots , citrus fruits , apples , strawberries and peanuts are particularly sensitive to salt.
Forms of salinization
Depending on the minerals occurring, typical soil forms are formed.
Solontchak
The Solontschak (from sol = salt and shak = salty area) is a typical salinization phenomenon with easily soluble salts. According to the World Reference Base for Soil Resources (WRB), Solontschak, like Solonetz, is a water-influenced soil and thus a typical phenomenon in the case of incorrect irrigation. There are around 300 million hectares of Solontschak worldwide. Typically, salt crusts easily form in depressions in the Solontschak, the soils are firm and there is little biological activity in the soils.
Solo network
Solonetz (from sol = salt and etz = strong characteristics) occurs on soils that are clay-enriched in the subsoil and have high concentrations of sodium. Like the Solontschak, they belong to the water-affected soils according to the WRB. Around 135 million hectares worldwide are affected by this form of salinization. These soils have high pH values (> 8.5).
Calcisol
Like gypsisol, calcisol is one of the salt accumulation soils (WRB). It arises from the precipitation of secondary carbonate. Calcisols are estimated to be around 1 billion hectares worldwide. Here secondary carbonate accumulates in deeper soil layers and the calcareous starting material is often no longer available.
Gypsisol
Gypsisol (from gypsum = gypsum ) is created like calcisol. In contrast to this, it is not carbonates that accumulate, but instead gypsum ( calcium sulfate ). Around 100 million hectares worldwide are affected by this form.
literature
- Scheffer / Schachtschabel (2010) Textbook of Soil Science , 16th edition, Springer Verlag; Chapter 8.4.3 to 8.4.6.
Individual evidence
- ↑ a b c d e Factsheet 4 on Sustainable Agriculture and Soil Protection - Soil Quality Deterioration , European Communities, May 2009
- ↑ Technical sign language lexicon of gardening and landscaping of the University of Hamburg: Salinization ( Memento of the original from March 5, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ↑ a b c d e f g h i j k l m n o p q r s t u v w Thomas Caspari (2007) Soils of the alternately dry tropics: salinization ; Script for the "Specialization Block Tropical Soils" of the Institute for Soil Science and Forest Nutrition at the Albert-Ludwigs-Universität Freiburg, online ( Memento of the original from February 27, 2014 in the Internet Archive ) Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ↑ Website of the Professorship for Groundwater and Hydromechanics - Soil Salinization ( Memento of the original from March 3, 2014 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. , ETH Zurich, accessed on February 28, 2014.
