What Is Soil Salinization?
Salinization of soil is an excessive accumulation of water-soluble salts. Typically, it is table salt NaCl. The list is far more extensive and includes various compounds of sodium, potassium, calcium, magnesium, sulfates, chlorides, carbohydrates, and bicarbonates. In general, salt-affected earths are categorized as saline, sodic and saline-sodic, depending on the content.
The major soil salinity effect on plant growth is tampering with water absorption. Even with sufficient soil moisture, crops wade and die due to the inability to take up enough water. At a global span, according to the report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) of 2018:
about 190 million acres are completely lost;
150 million acres are damaged;
2.5 billion acres are impacted by salinization.
What Causes Soil Salinization?
Soil salinization occurs when soluble salts are retained in the earth. It happens either naturally or because of improper anthropogenic activities, particularly farming practices. Besides, some earths are initially saline due to low salt dissolution and removal. Soil salinization causes include:
1.dry climates and low precipitations when excessive salts are not flushed from the earth;
2.high evaporation rate, which adds salts to the ground surface;
3.poor drainage or waterlogging when salts are not washed due to a lack of water transportation;
4.irrigation with salt-rich water, which amplifies salt content in earths;
5.removal of deep-rooted vegetation and a raised water table as a consequence;
6.leakage from geological deposits and penetration into groundwater;
7.sea-level rise when sea salts seep into lower lands;
8.breezes in the coastal areas that blow salty air masses to the nearby territories;
9.seawater submergence followed by salt evaporation;
10.inappropriate application of fertilizers when excess nitrification accelerates soil salinization.
Indicators Of Soil Salinity
Salinization can be noticed visually by analyzing the soil surface, speed of water infiltration, and vegetation state. As salinization proceeds, signs get more severe. For example, slight whitening on the surface changes into distinct salt crystals. Apart from visual changes, there are indirect indicators of extra salt concentration. These are poorer water quality or animal behavior when livestock refuses to drink water due to its salty taste.
Surface Changes Because Of Salinization
1.damp areas and waterlogging;
2.ground whitening at early stages and salt crystals at late ones;
3.increased water level in furrows;
4.bare soils (where plants fail to grow due to salinization);
5.deterioration of roads, buildings, etc.;
6.white or dark circles around water bodies.
Salinization-Related Indicators In Vegetation
1.plant withering;
2.crop loss;
3.reduction of biodiversity;
4.appearance of salt-tolerant plants in the area and their further dominance.
Soil Salinity Measurement
Apart from visual estimation, there are more reliable methods to measure soil salinity, e.g., to assess the earth’s electric conductivity with specific devices. With a rise of salt concentration in the solution, its conductivity rises, too. Other types of soil salinity tests find out the exchangeable sodium percentage or sodium absorption ratio.
Besides laboratory tests, salinization is estimated on farmlands or remotely. Salinity sensors are used for monitoring surface soil salinity in the field. Satellites retrieve data with SWIR and NIR bands for remote sensing analytics of water absorption and its possible correlation with salinity.
Adverse Effects Of Salinization
Soil salinization consequences are far from positive, covering multiple aspects of ecology and human life. It affects crop production and water supply industries, induces the risk of floods and soil erosion, and decreases biodiversity.
Agricultural Production
Water saturation in plants depends on the level of salts in groundwater and the plant itself. Water is absorbed in the process of osmosis and flows from less salt-concentrated areas to more concentrated ones. When the salt concentration is too high, it means that the soil’s osmotic potential is essentially negative. Plants suffer from osmotic stress when they fail to take up water, even when it is present in the soil. Basically, the process is similar to drought stress due to a lack of moisture in the ground. As a result, vegetation dies. Salinization tampers with nitrogen uptake too, which slows plant development and causes a yield loss.
Another soil salinity effect on agriculture is ionic stress due to harmful ions in soil salts, e.g., chloride or sodium. Apart from their toxic impact as such, these positively charged ions impede the acquisition of other positively charged ions vital for crop growth (particularly potassium and calcium). The result is the same as with osmotic stress due to salinization – vegetation dies.
Cropland Soil Salinization and Associated Hydrology:
Trends, Processes and Examples
While global food demand and world population are rapidly growing, land potential for cropping is steadily declining due to various soil degradation processes, a major one of them being soil salinization. Currently, approximately 20% of total cropland and 33% of irrigated agricultural land are salinized as a result of poor agricultural practices and it is expected that by 2050, half of the croplands worldwide will become salinized. Thus, there is a real need to better understand soil salinization processes and to develop agricultural practices that will enable production of the needed amount of food to feed humanity, while minimizing soil salinization and other degradation processes. The major sources of solutes in agricultural environments are: (i) the soil itself, and the parent geological material; (ii) shallow and salt rich groundwater; and (iii) salt rich irrigation water. The salinization of soil is a combination of transport of solutes towards the root zone to replenish evaporation and transpiration and limited washing of the soil by rain or irrigation. Therefore, most salinized soils are present in arid and semi-arid environments where precipitation is low and evaporation is high. In this manuscript, examples of soil salinization processes from croplands around the world will be presented and discussed to bring attention to this important topic, to present the latest scientific insights and to highlight the gaps that should be filled, from both scientific and practical perspectives.
Contrasting effects of aridity and seasonality on global salinization
Soil salinization is the most diffuse form of soil degradation in drylands, where it represents a rising threat to crop production and ecosystem functioning. While aridity is thought to be the main driver of salt accumulation, the role played by other forms of climatic forcing, such as rainfall seasonality and synchronicity between precipitation and atmospheric water demand, remains uncertain. Here, we use a combination of global climatic data, soil observations and ecohydrological models to show that average precipitation and seasonality have contrasting impacts on soil salinization. Aridity enhances salinization by lowering soil moisture and suppressing leaching events. By contrast, rainfall seasonality can reduce salt accumulation in the soil by boosting percolation during the wet season, when salt removal efficiency is greatest. Consequently, salt removal is more effective in regions where seasonality is coupled with strong a synchronicity between water supply and demand, such as in Mediterranean climates. As a result, neglecting the interplay of aridity, seasonality and a synchronicity may lead to inaccurate assessments of the impacts of climate on global soil salinization.
Where does salinity occur and why?
Primary salinity occurs naturally in soils and waters. Examples of naturally occurring saline areas include salt lakes, salt pans, salt marshes and salt flats. Secondary salinity is salting that results from human activities, usually land development and agriculture.
What causes salinisation in soil?
Causes of irrigation salinity
The salt remains behind in the soil when water is taken up by plants or lost to evaporation. Recharge rates in irrigation areas can be much higher than dryland areas due to leakage from both rainfall and irrigation. This causes potentially very high salinisation rates.
Does salt make land infertile?
Large quantities of the salts dissolved in the water, such as sodium and chloride, are diffused into the soil and remain there after the water has evaporated. The salt stunts the crops and can even make soils infertile in the long run. … And that is for a reason: “Our crop plants are the result of many years of breeding.
How can salinization be prevented?
Here are some typical methods to prevent soil salinization: Optimize irrigation (reduce salty water usage, implement drip irrigation, use desalinated, recycled, rain-harvested water, and don’t overirrigate). Add organic matter and manure to keep moisture and reduce irrigation.
How is salinity caused by humans?
Human activities can cause salinization through the use of salt-rich irrigation water, which can be exacerbated by overexploitation of coastal groundwater aquifers causing seawater intrusion, or due to other inappropriate irrigation practices, and/or poor drainage conditions.
Is salinity a problem?
Salinity affects: farms – salinity can decrease plant growth and water quality resulting in lower crop yields and degraded stock water supplies. Excess salt affects overall soil health, reducing productivity. It kills plants, leaving bare soil that is prone to erosion.
Is soil salinity good or bad?
Although increasing soil solution salinity has a positive effect on soil aggregation and stabilization, at high levels salinity can have negative and potentially lethal effects on plants. As a result, salinity cannot be increased to maintain soil structure without considering potential impacts on plant health.
What country in Asia has a serious salinization problem?
In the Maldives, an FAO survey shows that the top soil has been largely cleaned from salinity by recent rains. On parts of the east coast of Sri Lanka and the West coast of Aceh, heavy rains have also cleaned most of the polluted land.
Which decreases the level of soil salinization?
Most of saline soils contain calcites and calcium salts of extremely low solubility (Qadir et al., 2002). … Most common chemical treatment toward saline soil is gypsum treatment. These treatments result in decrease in soil salinity and sodicity (Qadir et al., 2002).
What are the effects of salinization?
Salinity affects production in crops, pastures and trees by interfering with nitrogen uptake, reducing growth and stopping plant reproduction. Some ions (particularly chloride) are toxic to plants and as the concentration of these ions increases, the plant is poisoned and dies.
Why is salinization a problem?
The problem of soil salinization isa scourge for agricultural productivity worldwide. Crops grown on saline soils suffer on an account of high osmotic stress, nutritional disorders and toxicities, poor soil physical conditions and reduced crop productivity.
What is salinization process?
7.1 Salinization
Most irrigation waters contain some salts. After irrigation, the water added to the soil is used by the crop or evaporates directly from the moist soil. The salt, however, is left behind in the soil. If not removed, it accumulates in the soil; this process is called salinization (see Fig. 102).
What is salinization and how does it occur?
Salinization is the process by which water-soluble salts accumulate in the soil. Salinization is a resource concern because excess salts hinder the growth of crops by limiting their ability to take up water. Salinization may occur naturally or because of conditions resulting from management practices.
What is a high salinity level?
Salinity is either expressed in grams of salt per kilogram of water, or in parts per thousand (ppt, or ‰). … Depending on their location and source of fresh water, some estuaries can have salinities as high as30 ppt. Seawater is on average 35 ppt, but it can range between 30 – 40 ppt.
How do you increase the salinity of water?
Evaporation of ocean water and formation of sea ice both increase the salinity of the ocean. However these “salinity raising” factors are continually counterbalanced by processes that decrease salinity such as the continuous input of fresh water from rivers, precipitation of rain and snow, and melting of ice.
How much land is affected by salinity?
Currently5%of New South Wales is affected by dry land salinity, and around 50% is under threat.
Why are it expressed parts per thousand instead of percent?
Why is salinity expressed in parts per thousand instead of percent? Salinity is expressed in parts per thousand because the proportion of dissolved substances in seawater is very small. … Explain how the salinity of water in polar regions varies seasonally.
What are three classes of salty soil?
Saline soils are usually categorized into three types, ie, saline, sodic, and alkaline sodic soil. Saline soil contains a lower amount of Na adsorbed onto soil particles. This type of soil is often seen in sandy soil containing lower amounts of clay and organic matter.
Why is ground water salty?
What causes groundwater salinity? Small quantities of salt are deposited onto the landscape every time it rains. Evaporation and plant transpiration remove water from the landscape but leave the salt behind. This concentrates salt over time.
Is salt good for soil?
Salt dehydrates plants and disrupts the internal water balance of plant cells. Salt is best used for small-scale gardening where it will be easily diluted by rain or watering, however. If salt is used on a large scale, it can create soil conditions that are not suitable for growing plants for quite some time.
What is the most salt tolerant crop?
Most of the major cereal crops exhibit high tolerance to soil salinity. In this group are sorghum, wheat, triticale, ripe, oats and barley. Only exceptions are corn and rice. All cereals tend to follow the same sensitivity or tolerance pattern in relation to their stage of growth.
What kind of pollution leads to salinization?
Salinization is caused by flooding or inundation with saline waters, breaching of dykes, storm surges, tsunamis, or the drying of large inland water bodies. Salinization can result where irrigation waters are compromised by salinity.