how does soil become saline

Soil salinization causes include:

• dry climates and low precipitations when excessive salts are not flushed from the earth;
• high evaporation rate, which adds salts to the ground surface;
• poor drainage or waterlogging when salts are not washed due to a lack of water transportation;
• irrigation with salt-rich water, which amplifies salt content in earths;
• removal of deep-rooted vegetation and a raised water table as a consequence;

Full Answer

What causes soil to become saline?

Over long periods of time, as soil minerals weather and release salts, these salts are flushed or leached out of the soil by drainage water in areas with sufficient precipitation. In addition to mineral weathering, salts are also deposited via dust and precipitation. Salts may accumulate in dry regions, leading to naturally saline soils.

What is soil salinity and why does it matter?

Visibly salt-affected soils on rangeland in Colorado. Salts dissolved from the soil accumulate at the soil surface and are deposited on the ground and at the base of the fence post. Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water.

How are salts deposited in soil?

In addition to mineral weathering, salts are also deposited via dust and precipitation. Salts may accumulate in dry regions, leading to naturally saline soils. This is the case, for example, in large parts of Australia. Human practices can increase the salinity of soils by the addition of salts in irrigation water.

What is the process of soil salination?

Salinization of soil results from a combination of evaporation, salt precipitation and dissolution, salt transport, and ion exchange ( Shimojima et al., 1996 ).

How is saline soil formed?

Saline soils are formed whenever climate, soil and hydrological conditions favour accumulation of soluble salts in the root zone. Arid and semi-arid regions of low rain fall and high temperature leads to less leaching, more evaporation of water and less transport of soluble salts.

What does it mean when soil is considered saline?

Saline soil is a term used to describe excessive levels of soluble salts in the soil water (soil solution), high enough to negatively affect plant growth, resulting in reduced crop yields and even plant death under severe conditions (Figure 1).

At what concentration soil becomes saline?

Soil salinity is usually determined from an extract of saturated paste of soil and then EC is termed as ECe. When 4 < ECe < 8, soil is termed as slightly saline. When 8 < ECe < 16, soil is termed as moderately saline. When ECe > 16, soil is termed as highly saline.

How do you know if soil is saline?

The standard procedure for salinity testing is to measure EC of a solution extracted from a soil wetted to a "saturation paste." According to U.S. Salinity Laboratory Staff (1954), a saline soil has an EC of the saturated paste extract of more than 4 dS/m, a value that corresponds to approximately 40 mmol salts per ...

How can you tell if soil is saline?

In field conditions, saline soils can be recognized by the spotty growth of crops and often by the presence of white salt crusts on the surface. When the salt problem is only mild, growing plants often have a blue-green tinge. Barren spots and stunted plants may appear in cereal or forage crops growing on saline areas.

What happens if soil is too saline?

If the level of salts in the soil water is too high, water may flow from the plant roots back into the soil. This results in dehydration of the plant, causing yield decline or even death of the plant. Crop yield losses may occur even though the effects of salinity may not be obvious.

Which soil has natural saline?

Arid soilArid soil is generally sandy in texture and saline in nature. It contains high salt and low humus content. Arid soils are made fertile by adding gypsum.

Which chemical is used for saline soil?

In Saline–sodic soils reclamation involves the addition of good-quality water to remove excess soluble salts and the use of a Ca2+ source (CaSO4 2H2O or CaCl2) to exchange Na+ from the soil as a soluble salt, Na2SO4. In Saline–sodic soils a saltwater-dilution method is usually effective in reclamation.

Can plants grow in saline soil?

Saline soils. Crops tolerant include cotton, alfalfa, cereals, grain sorghum, sugar beets, Bermuda grass, tall wheat grass and Harding grass. Salinity higher than desirable for greenhouse soils.

How do you fix salinity in soil?

Managing salinity involves striking a balance between the volume of water entering (recharge) and leaving (discharge) the groundwater system. The water table can be lowered by: planting, regenerating and maintaining native vegetation and good ground cover in recharge, transmission and discharge zones, where possible.

What crops grow in saline soil?

7.3 Crops and saline soilsHighly tolerantModerately tolerantSensitiveBarleyTomatoPeasSugarbeetOatsBeansCottonAlfalfaSugarcaneAsparagusRicePear11 more rows

What is the difference between saline and sodic soils?

Saline soils often exhibit white salt deposits or crusts, visible at the soil surface. Saline soils typically do not display poor soil structure, and as a result, they have adequate water infiltration rates. Sodic soils have a high amount of exchangeable sodium on the cation-exchange sites.

How does salinity affect plant growth?

In order to assess the tolerance of plants to salinity stress, growth or survival of the plant is measured because it integrates the up- or down-regulation of many physiological mechanisms occurring within the plant. Osmotic balance is essential for plants growing in saline medium. Failure of this balance results in loss of turgidity, cell dehydration and ultimately, death of cells. On the other hand, adverse effects of salinity on plant growth may also result from impairment of the supply of photosynthetic assimilates or hormones to the growing tissues (Ashraf, 2004). Ion toxicity is the result of replacement of K+by Na+in biochemical reactions, and Na+and Cl−induced conformational changes in proteins. For several enzymes, K+acts as cofactor and cannot be substituted by Na+. High K+concentration is also required for binding tRNA to ribosomes and thus protein synthesis (Zhu, 2002). Ion toxicity and osmotic stress cause metabolic imbalance, which in turn leads to oxidative stress (Chinnusamy et al., 2006). The adverse effects of salinity on plant development are more profound during the reproductive phase. Wheat plants stressed at 100–175 mM NaCl showed a significant reduction in spikelets per spike, delayed spike emergence and reduced fertility, which results in poor grain yields. However, Na+and Cl−concentrations in the shoot apex of these wheat plants were below 50 and 30 mM, respectively, which is too low to limit metabolic reactions (Munns and Rawson, 1999). Hence, the adverse effects of salinity may be attributed to the salt-stress effect on the cell cycle and differentiation. Salinity arrests the cell cycle transiently by reducing the expression and activity of cyclins and cyclin-dependent kinases that results in fewer cells in the meristem, thus limiting growth. The activity of cyclin-dependent kinase is diminished also by post-translational inhibition during salt stress. Recent reports also show that salinity adversely affects plant growth and development, hindering seed germination, seedling growth, enzyme activity (Seckin et al., 2009), DNA, RNA, protein synthesis and mitosis (Tabur and Demir, 2010; Javid et al., 2011).

How does salinity affect agriculture?

Agricultural crops exhibit a spectrum of responses under salt stress. Salinity not only decreases the agricultural production of most crops, but also, effects soil physicochemical properties, and ecological balance of the area. The impacts of salinity include—low agricultural productivity, low economic returns and soil erosions, (Hu and Schmidhalter, 2002). Salinity effects are the results of complex interactions among morphological, physiological, and biochemical processes including seed germination, plant growth, and water and nutrient uptake (Akbarimoghaddam et al., 2011; Singh and Chatrath, 2001). Salinity affects almost all aspects of plant development including: germination, vegetative growth and reproductive development. Soil salinity imposes ion toxicity, osmotic stress, nutrient (N, Ca, K, P, Fe, Zn) deficiency and oxidative stress on plants, and thus limits water uptake from soil. Soil salinity significantly reduces plant phosphorus (P) uptake because phosphate ions precipitate with Ca ions (Bano and Fatima, 2009). Some elements, such as sodium, chlorine, and boron, have specific toxic effects on plants. Excessive accumulation of sodium in cell walls can rapidly lead to osmotic stress and cell death (Munns, 2002). Plants sensitive to these elements may be affected at relatively low salt concentrations if the soil contains enough of the toxic element. Because many salts are also plant nutrients, high salt levels in the soil can upset the nutrient balance in the plant or interfere with the uptake of some nutrients (Blaylock et al., 1994). Salinity also affects photosynthesis mainly through a reduction in leaf area, chlorophyll content and stomatal conductance, and to a lesser extent through a decrease in photosystem II efficiency (Netondo et al., 2004). Salinity adversely affects reproductive development by inhabiting microsporogenesis and stamen filament elongation, enhancing programed cell death in some tissue types, ovule abortion and senescence of fertilized embryos. The saline growth medium causes many adverse effects on plant growth, due to a low osmotic potential of soil solution (osmotic stress), specific ion effects (salt stress), nutritional imbalances, or a combination of these factors (Ashraf, 2004). All these factors cause adverse effects on plant growth and development at physiological and biochemical levels (Munns and James, 2003), and at the molecular level (Tester and Davenport, 2003).

What is IST in plant pathogens?

The term Induced Systemic Tolerance (IST) has been proposed for PGPR-induced physical and chemical changes that result in enhanced tolerance to abiotic stress. PGPR facilitate plant growth indirectly by reducing plant pathogens, or directly by facilitating the nutrient uptake through phytohormone production (e.g. auxin, cytokinin and gibberellins), by enzymatic lowering of plant ethylene levels and/or by production of siderophores (Kohler et al., 2006). It has been demonstrated that inoculations with AM (arbuscular mycorrhizal) fungi improves plant growth under salt stress (Cho et al., 2006). Kohler et al., 2006demonstrated the beneficial effect of PGPR Pseudomonas mendocinastrains on stabilization of soil aggregate. The three PGPR isolates P. alcaligenesPsA15, Bacillus polymyxaBcP26 and Mycobacterium phleiMbP18 were able to tolerate high temperatures and salt concentrations and thus confer on them potential competitive advantage to survive in arid and saline soils such as calcisol (Egamberdiyeva, 2007). Kohler et al., 2009investigated the influence of inoculation with a PGPR, P. mendocina, alone or in combination with an AM fungus, Glomus intraradicesor G. mosseaeon growth and nutrient uptake and other physiological activities of Lactuca sativaaffected by salt stress. The plants inoculated with P. mendocinahad significantly greater shoot biomass than the controls and it is suggested that inoculation with selected PGPR could be an effective tool for alleviating salinity stress in salt sensitive plants. Bacteria isolated from different stressed habitats possess stress tolerance capacity along with the plant growth-promoting traits and therefore are potential candidates for seed bacterization. When inoculated with these isolates, plants show enhanced root and shoot length, biomass, and biochemical levels such as chlorophyll, carotenoids, and protein (Tiwari et al., 2011). Investigations on interaction of PGPR with other microbes and their effect on the physiological response of crop plants under different soil salinity regimes are still in incipient stage. Inoculations with selected PGPR and other microbes could serve as the potential tool for alleviating salinity stress in salt sensitive crops. Therefore, an extensive investigation is needed in this area, and the use of PGPR and other symbiotic microorganisms, can be useful in developing strategies to facilitate sustainable agriculture in saline soils.

What bacteria promotes wheat growth?

Applying the bacterial inocula increased the concentration of N, P, Fe and Mn in wheat shoots grown in normal and saline soil and thus concluded that Streptomyces isolate has potential to be utilized as biofertilizers in saline soils. More recently Ramadoss et al., 2013studied the effect of five plant growth promoting halotolerant bacteria on wheat growth and found that inoculation of those halotolerant bacterial strains to ameliorate salt stress (80, 160 and 320 mM) in wheat seedlings produced an increase in root length of 71.7% in comparison with uninoculated positive controls. In particular, Hallobacillus sp. and B. halodenitrificansshowed more than 90% increase in root elongation and 17.4% increase in dry weight when compared to uninoculated wheat seedlings at 320 mM NaCl stress indicating a significant reduction of the deleterious effects of NaCl. These results indicate that halotolerant bacteria isolated from saline environments have potential to enhance plant growth under saline stress through direct or indirect mechanisms and would be most appropriate as bioinoculants under such conditions. The isolation of indigenous microorganisms from the stress affected soils and screening on the basis of their stress tolerance and PGP traits may be useful in the rapid selection of efficient strains that could be used as bioinoculants for stressed crops. Some of the advances and researches carried out in evaluating role of rhizobacteria as salinity stress remediators have been summarized in Table 1.

What are the effects of salt on soil?

Rhizosphere microorganisms, particularly beneficial bacteria and fungi, can improve plant performance under stress environments and, consequently, enhance yield both directly and indirectly (Dimkpa et al., 2009). Some plant growth-promoting rhizobacteria (PGPR) may exert a direct stimulation on plant growth and development by providing plants with fixed nitrogen, phytohormones, iron that has been sequestered by bacterial siderophores, and soluble phosphate (Hayat et al., 2010). Others do this indirectly by protecting the plant against soil-borne diseases, most of which are caused by pathogenic fungi (Lutgtenberg and Kamilova, 2009). The problem of soil salinization is a 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. The present review focuses on the enhancement of productivity under stressed conditions and increased resistance of plants against salinity stress by application of plant growth promoting microorganisms.

How does salinity affect crop production?

Salinity is one of the most brutal environmental factors limiting the productivity of crop plants because most of the crop plants are sensitive to salinity caused by high concentrations of salts in the soil, and the area of land affected by it is increasing day by day. For all important crops, average yields are only a fraction – somewhere between 20% and 50% of record yields; these losses are mostly due to drought and high soil salinity, environmental conditions which will worsen in many regions because of global climate change. A wide range of adaptations and mitigation strategies are required to cope with such impacts. Efficient resource management and crop/livestock improvement for evolving better breeds can help to overcome salinity stress. However, such strategies being long drawn and cost intensive, there is a need to develop simple and low cost biological methods for salinity stress management, which can be used on short term basis. Microorganisms could play a significant role in this respect, if we exploit their unique properties such as tolerance to saline conditions, genetic diversity, synthesis of compatible solutes, production of plant growth promoting hormones, bio-control potential, and their interaction with crop plants.

How can salinization be reduced?

Salinization can be restricted by leaching of salt from root zone , changed farm management practices and use of salt tolerant plants. Irrigated agriculture can be sustained by better irrigation practices such as adoption of partial root zone drying methodology, and drip or micro-jet irrigation to optimize use of water. The spread of dry land salinity can be contained by reducing the amount of water passing beyond the roots. This can be done by re-introducing deep rooted perennial plants that continue to grow and use water during the seasons that do not support annual crop plants. This may restore the balance between rainfall and water use, thus preventing rising water tables and the movement of salt to the soil surface (Manchanda and Garg, 2008). Farming systems can change to incorporate perennials in rotation with annual crops (phase farming), in mixed plantings (alley farming, intercropping), or in site-specific plantings (precision farming) (Munns et al., 2002). Although the use of these approaches to sustainable management can ameliorate yield reduction under salinity stress, implementation is often limited because of cost and availability of good water quality or water resource. Evolving efficient, low cost, easily adaptable methods for the abiotic stress management is a major challenge. Worldwide, extensive research is being carried out, to develop strategies to cope with abiotic stresses, through development of salt and drought tolerant varieties, shifting the crop calendars, resource management practices etc. (Venkateswarlu and Shanker, 2009) as shown in Fig. 1.

What is salinity in irrigation?

Saline is incrustation in a PVC irrigation pipe from Brazil. Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinization. Salts occur naturally within soils and water.

How to reduce soil salinity?

Salinity is an important land degradation problem. Soil salinity can be reduced by leaching soluble salts out of soil with excess irrigation water. Soil salinity control involves watertable control and flushing in combination with tile drainage or another form of subsurface drainage. A comprehensive treatment of soil salinity is available from the United Nations Food and Agriculture Organization.

What are the effects of salinity on soil?

Consequences of soil salinity 1 Detrimental effects on plant growth and yield 2 Damage to infrastructure (roads, bricks, corrosion of pipes and cables) 3 Reduction of water quality for users, sedimentation problems, increased leaching of metals, especially copper, cadmium, manganese and zinc. 4 soil erosion ultimately, when crops are too strongly affected by the amounts of salts. 5 More energy required to desalinate

How can salt be added to soil?

Human practices can increase the salinity of soils by the addition of salts in irrigation water. Proper irrigation management can prevent salt accumulation by providing adequate drainage water to leach added salts from the soil. Disrupting drainage patterns that provide leaching can also result in salt accumulations. An example of this occurred in Egypt in 1970 when the Aswan High Dam was built. The change in the level of ground water before the construction had enabled soil erosion, which led to high concentration of salts in the water table. After the construction, the continuous high level of the water table led to the salination of the arable land.

Why is salinity increased in urban areas?

Salinity in urban areas often results from the combination of irrigation and groundwater processes. Irrigation is also now common in cities (gardens and recreation areas).

How does salinity occur in drylands?

Salinity in drylands can occur when the water table is between two and three metres from the surface of the soil. The salts from the groundwater are raised by capillary action to the surface of the soil. This occurs when groundwater is saline (which is true in many areas), and is favored by land use practices allowing more rainwater to enter the aquifer than it could accommodate. For example, the clearing of trees for agriculture is a major reason for dryland salinity in some areas, since deep rooting of trees has been replaced by shallow rooting of annual crops.

Why is sodic soil so difficult to grow?

Sodic soils present particular challenges because they tend to have very poor structure which limits or prevents water infiltration and drainage. They tend to accumulate certain elements like boron and molybdenum in the root zone at levels that maybe toxic for plants. The most common compound used for reclamation of sodic soil is gypsum, and some plants that are tolerant to salt and ion toxicity may present strategies for improvement.

How does salinity affect rice?

Soil salinity reduces rice crop productivity significantly . In coastal Bangladesh, several nonaltered (native) varieties of rice have already been growing in weakly saline soils but their productivity is compromised by soil salinity. Many of the native varieties of rice crops are not suitable for growth in strongly saline environments. High salinity levels may result in low yields and sterile grains. Since soil salinity in coastal Bangladesh is likely to increase significantly with saltwater intrusion due to sea level rise, the main challenge for rice breeding scientists in Bangladesh is to develop new varieties that can grow in soils with high salinity levels. Already BRRI has developed several new varieties of salt-tolerant rice. Most of them have been field tested successfully in saline soils in Satkhira, a coastal district in southwestern Bangladesh ( CCC, 2009 ). In general, soil salinity in Satkhira may be classified into four levels, ranging from low (<4 dS/m) to very high (>15 dS/m) ( Table 7.2 ). For field-testing of new varieties of rice crops some of the more specific soil-water parameters were monitored throughout their growing periods. These included salinity levels of:

How is salinity measured?

Soil salinity is measured by using electrical conductivity (EC) measurements of a water-saturated soil paste extract ( Table 14.1 ).

Why is salinity important for agriculture?

Soil salinity is among the most important stresses worldwide decreasing plant growth and agricultural production. The amount of arable land in the world is equal to 1.5 billion hectares, of which 77 million hectares are unsuitable for crop growth because of high salinity. The amount of land occupied by saline soils is increasing in many parts of the world, especially those under arid and semiarid conditions where precipitation is low and temperatures and rates of evaporation are high. Arid and semiarid lands cover more than 7% of the total land on the earth ( Selvakumar et al., 2014; Miransari, 2016 ).

What causes soil salinity?

Soils and lands that have shallow water tables can develop saline soils due to excessive water evaporation and the concentration of salts. Poor water quality and irrigation practices also contribute to the salinization of thousands of acres of farmland each year around the world. Salt-affected soils occupy, on a global basis, 952.2 million ha of land. These soils constitute nearly 7% of the total land area or nearly 33% of the potential agricultural land area of the world ( Gupta and Abrol, 1990 ).

How does salinity affect soil structure?

Soil structure, or the arrangement of soil particles, is critical in affecting permeability and infiltration.

What is salinity in agriculture?

Salinity is a soil and water quality concern, especially in arid and semiarid areas where water demand is increasing day by day for irrigation and agriculture. Arid and semiarid areas are the regions where there are insufficient rain to leach salts and excess sodium ions out of the rhizosphere.

What is the relative growth of plants in the presence of salinity?

The relative growth of plants in the presence of salinity is termed their salt tolerance ( Agri-Facts, 2001 ). Salt tolerances are usually measured by electrical conductivity of a saline solution (that is its ability) to transmit an electrical current.

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:

How does salinization affect agriculture?

Salinization of soil negatively impacts plant development and induces land degradation. Saline earths show lower agricultural productivity, worsen farmers’ wellbeing, and the economic situation in the region. Managing soil salinity at early stages helps to reverse it. However, heavy contamination leads to complete loss of farmlands ...

What is salinization of soil?

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.

Why does soil salinize?

Soil salinization causes include: dry climates and low precipitations when excessive salts are not flushed from the earth; high evaporation rate, which adds salts to the ground surface; poor drainage or waterlogging when salts are not washed due to a lack of water transportation;

How does salinity affect plants?

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.

How many acres of land have been lost due to salinization?

The United Nations University states that about 5,000 acres have been lost daily all over the world because of salinization since the 1990s, as of 2014.

Why is crop monitoring important?

Crop Monitoring may assist the process of reducing soil salinity. Shallow-rooted plants may not reach subsoil moisture, and extra subsoil moisture may induce salinity. Crop Monitoring provides reports on surface soil moisture and root-zone moisture, facilitating the choice of crops for planting in the exact areas.

How does salinization affect rice?

Soil salinization is a widespread problem and a major abiotic constraint affecting the global food production and threatening food security. Plant growth, development and yield are severally reduced under saline conditions. Rice (Oryza sativa L.) is the staple food in many countries which feeds millions of people across the world. However, rice plant, being glycophyte in nature, is sensitive to salinity which results in several adverse morphological, physiological, biochemical, and molecular changes leading to reduction in biomass production and grain yield. Effects of salinity on rice occur at two stages that is, at the initial phase of plant development the osmotic effects rapidly reduce plant growth and the second slow phase of plant response to salinity when symptoms of salinity-induced toxicity appear. At morphological levels, shoot and root growth, above- and below-ground biomass production, number of tillers and spikelets and grain yield of rice are adversely affected. Disruption in photosynthetic activity and pigment production, membrane permeability and integrity, Na + /K + balance across the membrane and production of reactive oxygen species causing oxidative damage are the major responses of rice at physiological level. In addition to agronomic practices to reduce soil salinity, salt tolerance cultivar of rice have been developed containing traits such as ion exclusion and tolerance of both the osmotic and tissue effects of salinity. The modern biotechnological marker-based genetic engineering approaches have helped the researchers to use a combination of genes to develop salt-tolerant and high yielding rice varieties. The other approaches to reduce salinity stress in plants include the use of salt-tolerant microbial inoculants/biofertilizers, silicon and manganese fertilization and phytohormones.

How much salinization affects the Mediterranean?

Soil salinization affected about 1–3 million hectares especially in the Mediterranean countries where irrigation farming is very common and many fields have reached soil salinity levels which prevents farmers from raising common crops.

What is salinization of soil?

Soil salinization is often associated with sodic soil. Natural or anthropogenic accumulation of sodium in the system leads to gradual replacement of divalent cations with Na + on the exchange complex of clay minerals.

What is the most serious environmental problem in Australia?

In Australia, soil salinization is the most severe environmental problem of the continent, causing a dramatic change in landscape, industry, and the future of farmland ( Dehaan and Taylor, 2002 ). The accumulation of soluble salts in soil occurs when evaporation exceeds precipitation and salts are not leached but remain in ...

How much of Egypt's land is salinized?

In Egypt, almost 35% of the agricultural land suffers from salinity ( Kotb et al., 2000; Kim and Sultan, 2002 ). Soil salinization is the first stage of environmental destruction caused by salinity and is interrelated with river and lake salinization.

Why are poaceae important?

Poaceae is the most economically important plant family because 70% of all crops are salt-sensitive grasses. About 3.6 billion ha from 5.2 billion ha of the world’s agricultural land is already salt-affected and not suitable for conventional crop farming. In contrast, the demand for food is continuously increasing and we expect to need to feed around nine billion by the end of 2050 ( Millar and Roots, 2012 ). However, extensive efforts are underway to improve the salinity tolerance of conventional crops either through breeding or modern molecular techniques, but still no crop can tolerate half the level of salinity of seawater. In such a scenario, a major breakthrough in crop breeding for salinity tolerance is needed. Regulation of the number, size, and shape of the salt-excreting structure—trichome could be one such possibility. About 15% of halophytic grasses excrete Na + and Cl − through bicellular microhairs, which are present on the leaf surface ( Adams et al., 1998 ). Aeluropus lagopoides (Linn.) Trin. Ex Thw. is a salt-excreting, salinity- (1000 mmol L −1 NaCl; Gulzar et al., 2003) and drought-tolerant ( Mohsenzadeh et al., 2006) grass. Therefore, it could be used as a model plant to improve the salinity tolerance of crops like rice, wheat, and maize ( Flowers and Colmer, 2008 ). Detailed ecological and physiological studies on A. lagopoides have been carried out ( Waghmode and Joshi, 1982; Sher et al., 1994; Abarsaji, 2000; Gulzar et al., 2003 ). However, information related to the function of its Na + transport genes in salinity is lacking. Therefore, the goals of this study were: (i) to isolate the cDNA sequences of VNHX and PMNHX from A. lagopoides; (ii) to observe the change in the expression of both genes under saline condition; and (iii) to explore the role of both genes in the salt tolerance of A. lagopoides.

What is the process of soil salinization?

Soil salinization is a major process of land degradation that decreases soil fertility and is a significant component of desertification processes in the world’s dryland (Thomas and Middleton, 1993 ).

Why is saline soil good for soil?

Excess salts keep the clay in saline soils in a flocculated state so that these soils generally have good physical properties. Structure is generally good and tillage characteristics and permeability to water are even better than those of non-saline soils. However, when leached with a low salt water, some saline soils tend to disperse resulting in low permeability to water and air, particularly when the soils are heavy clays. Leaching may also result in a slight increase in soil pH due to lowering of salt concentration but saline soils, as will be shown later, rarely become strongly sodic upon leaching if there is an adequate drainage system.

What are the characteristics of saline soil?

The distinguishing characteristic of saline soils from the agricultural standpoint, is that they contain sufficient neutral soluble salts to adversely affect the growth of most crop plants. For purposes of definition, saline soils are those which have an electrical conductivity of the saturation soil extract of more than 4 dS/m at 25°C (Richards 1954). This value is generally used the world over although the terminology committee of the Soil Science Society of America has lowered the boundary between saline and non-saline soils to 2 dS/m in the saturation extract. Soluble salts most commonly present are the chlorides and sulphates of sodium, calcium and magnesium. Nitrates may be present in appreciable quantities only rarely. Sodium and chloride are by far the most dominant ions, particularly in highly saline soils, although calcium and magnesium are usually present in sufficient quantities to meet the nutritional needs of crops. Many saline soils contain appreciable quantities of gypsum (CaSO 4, 2H 2 O) in the profile. Soluble carbonates are always absent. The pH value of the saturated soil paste is always less than 8.2 and more often near neutrality (Abrol et al., 1980). Physico-chemical characteristics in respect of a few typical saline soil profiles are presented in Tables 5-8.

What does saline soil mean?

In field conditions, saline soils can be recognized by the spotty growth of crops and often by the presence of white salt crusts on the surface. When the salt problem is only mild, growing plants often have a blue-green tinge. Barren spots and stunted plants may appear in cereal or forage crops growing on saline areas. The extent and frequency of bare spots is often an indication of the concentration of salts in the soil. If the salinity level is not sufficiently high to cause barren spots, the crop appearance may be irregular in vegetative vigour.

Why is it important to know about saline soil?

Crop plants differ a great deal in their ability to survive and yield satisfactorily when grown in saline soils. Information on the relative tolerance of crops to a saline soil environment is of practical importance in planning cropping schedules for optimum returns. There are situations where farmers have to live with salinity problems, for example, in areas having saline water as the only source of water for irrigation. In other situations where good quality water is available for reclamation of saline soils, it is often helpful to grow crops simultaneously with reclamation efforts to make reclamation economic.

How to flush salts from soil?

Flushing: Washing away the surface accumulated salts by flushing water over the surface is sometimes used to desalinize soils having surface salt crusts. Because the amount of salts that can be flushed from a soil is rather small, this method does not have much practical significance.

How do salts affect plant growth?

The effect of dissolved salts on plant growth depends on their concentration in the soil solution at any particular time but it is extremely difficult to measure the soil solution concentration at the usual field moisture contents due to sampling problems. A simplified procedure consists of mixing a soil sample with sufficient water to produce a saturated paste and then extracting the solution for measurement of conductivity. Measuring the electrical conductivity (EC) of a saturation extract has an advantage in that saturation percentage is directly related to field moisture range. Over a considerable textural range, saturation percentage is approximately four times the moisture content held at fifteen atmospheres which closely approximates the wilting percentage. The soluble salt concentration in the saturation extract therefore tends to be about one-half of the concentration of the soil solution at the upper end of the field available moisture range and about one-fourth the concentration that the soil solution will have at the dry end of the available moisture range (Richards, 1954).

What is the standard unit of conductance?

The standard unit of conductance is siemens (see Table 9) and when expressed per unit of distance, the standard unit of conductivity is siemens per metre. The conductivity of most saturation paste extracts is only a fraction of a siemens per metre. For convenience, therefore, conductivities of soil extracts are expressed in deci Siemens (mS) per metre at 25°C.

How to reclamate saline soil?

Saline soil reclamation requires leaching the soil with enough non-saline water that salts are moved below the root zone. Adequate drainage is absolutely necessary for this procedure to be successful. Research in the western United States has shown that substantial water volumes are needed to leach salt from the soil. Application of reclamation water by sprinkler irrigation or repeated pulsing of small applications of water (as opposed to flood irrigation) is the preferred method, as leaching is more thorough in an unsaturated soil. Whether leaching with a sprinkler or a flood irrigation system, testing the soil for EC following treatment will help assess the effectiveness of reclamation.

Why does SAR increase in a stream?

The SAR of a stream is dependent on the amount of sodium in the stream relative to the amount of calcium and magnesium. If sodium is a significant component of irrigation return flow , the SAR of the stream could increase during low flow. Similarly, if evaporation is extensive, this may also cause SAR to increase due to concentration of salts and precipitation of calcium as limestone.

What is the SAR of sodic water?

Sodic water is defined as having a SAR greater than 12.

Why is gypsum added to soil?

Gypsum is generally added to provide a calcium source to displace sodium in the soil. (Gypsum is calcium sulfate, 22.5% calcium). For most soils in Montana east of the continental divide, the soil is already saturated with respect to calcium (as calcium carbonate or lime). Hence, adding gypsum to a soil already saturated with calcium simply elevates the concentration of calcium, favoring formation of calcium carbonate.

What is the process of water moving laterally?

This process is called saline seep. For more information, refer to the Montana Salinity Control Association .

How does salinity change in a stream?

Generally, salinity decreases as stream flow increases and increases with decreasing stream flow. The same is true for SAR. In many high plains streams, salinity may rise with the first flush of runoff water due to bank flushing, which washes salt off the soil adjacent to streams. Stream flow generally decreases after spring snow melt and runoff from higher elevations ends. When the river goes through rising and falling stages due to rain (especially thunderstorms), the EC is usually lower when the river level is falling, rather than rising. For a good report on this topic read the USGS Publication "U.S. Geological Survey Monitoring of Powder River Basin Stream Water Quantity and Quality."

What soil class has more than 30% clay?

1/ Risk of dispersion, swelling, and crusting applies especially to soils with more than 30% clay: clay loam, silty clay loam, sandy clay loam, or silty clay textural classes.

Overview

Natural occurrence

Salts are a natural component in soils and water. The ions responsible for salination are: Na , K , Ca , Mg and Cl .
Over long periods of time, as soil minerals weather and release salts, these salts are flushed or leached out of the soil by drainage water in areas with sufficient precipitation. In addition to mineral weathering, salts are also deposited via dust and precipitation. Salts may accumulate in …

Sodic soils

Dry land salinity

Salinity due to irrigation

Consequences of soil salinity

Salt tolerance of crops

See also