What are the best methods to treat high salinity of clay soil?

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What are the best methods to treat high salinity of clay soil?

Dear All,

Here in Pakistan we are struggling these days with the salinity of soil problem. The soil types varies from clay to loamy clay and the primary crops grown are rice and sessional vegetable. The irrigation methods adopted are traditional and we know that the over irrigation has rested in this problem. You can see in the picture the severity of the problem.

We are planning to undertake some action research for developing appropriate and location specific soil reclamation technologies to solve this soil salinity problem. Please suggest what are the best methods to treat the saline soil without loosing any crop season. 

 

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23 Answers

  1. What is soil salinity  - Soil salinity is the salt content in the soil; the process of increasing the salt content is known as salinisation. Salt is a natural element of soils and water. The ions responsible for salination are: Na+, K+, Ca2+, Mg2+ and Cl-.

    causes of salinity -  The excess accumulation of salts, typically most pronounced at the soil surface, can result in salt-affected soils. Salts may rise to the soil surface by capillary transport from a salt-laden water table and then accumulate due to evaporation. They can also become concentrated in soils due to human activity, for example the use of potassium as fertilizer, which can form sylvite, a naturally occurring salt. As soilsalinity increases, salt effects can result in degradation of soils and vegetation.

    Salinization as a process can result from:

    • high levels of salt in water.
    • landscape features that allow salts to become mobile (movement of water table).
    • climatic trends that favor accumulation.
    • human activities.

    Measuring Soil Salinity -  Salinity is measured by passing an electrical current through a soil solution extracted from a saturated soil sample. The ability of the solution to carry a current is called electrical conductivity (EC). EC is measured in deciSiemens per meter (dS/m), which is the numerical equivalent to the old measure of millimhos per centimeter. The lower the salt content of the soil, the lower the dS/m rating and the less the effect on plant growth. Soil samples taken for soil fertility purposes are adequate for looking for trends in salinity, but may not provide the same information as sampling targeted for diagnosing salinity. Refer to 0.521, Diagnosing Saline and Sodic Soil Problems for more detail on assessing saline soil conditions.

    Soil salinity can also be measured in the field with electromagnetic conductivity meters. This technology works through the use of a transmitting coil that induces a magnetic field into the soil. 

    Effect on crops - Excess soil salinity causes poor and spotty stands of crops, uneven and stunted growth and poor yields, the extent depending on the degree of salinity. The primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. This is because the osmotic pressure of the soil solution increases as the salt concentration increases. Apart from the osmotic effect of salts in the soil solution, excessive concentration and absorption of individual ions may prove toxic to the plants and/or may retard the absorption of other essential plant nutrients.

    Reclamation and management - Saline soils cannot be reclaimed by chemical amendments, conditioners or fertilizers. A field can only be reclaimed by removing salts from the plant root zone. In some cases, selecting salt-tolerant crops may be needed in addition to managing soils.

    1. Salt leaching -  This is by far the most effective procedure for removing salts from the root zone of soils. Leaching is most often accomplished by ponding fresh water on the soil surface and allowing it to infiltrate. Leaching is effective when the salty drainage water is discharged through subsurface drains that carry the leached salts out of the area under reclamation. Leaching may reduce salinity levels in the absence of artificial drains when there is sufficient natural drainage, i.e. the ponded water drains without raising the water table. Leaching should preferably be done when the soil moisture content is low and the groundwater table is deep. Leaching during the summer months is, as a rule, less effective because large quantities of water are lost by evaporation. The actual choice will however depend on the availability of water and other considerations.

    2.   Drainage -  Irrigation is the most effective means of stabilizing agricultural production in areas where the rainfall is either inadequate for meeting the crop requirements or the distribution is erratic. Before the introduction to an area of large quantities of water through irrigation, there exists a water balance between the rainfall on the one hand and stream flow, groundwater table, evaporation and transpiration on the other. This balance is serously disturbed when additional quantities of water are artificially spread on the land to grow agricultural crops, introducing (Plates 3, 4a, 4b) additional factors of groundwater recharge from seepage from canals, distributors and field channels, most of which are unlined, and from the irrigation water let on to the fields over and above the quantities actually utilized by the crops, etc. As a result of these, the groundwater table rises. There are numerous instances throughout the world, where consequent upon the introduction of canal irrigation, the water table has risen considerably within 10 years to less than 2 m. Once the groundwater table is close to the soil surface, due to evaporation from the surface, appreciable movement of the groundwater takes place resulting in the accumulation of salts in the root zone. A schematic relationship between depth of groundwater and evaporation from the soil surface is shown in Figure 7. This relationship is significant and shows that there is a critical depth of water table above which there is a sharp increase in the evaporation rate and therefore soil salinization. In general, the critical depth of water table ranges between 1.5 to 3.0 metres depending on soil characteristics, root zone of crops, salt content of groundwater, etc: To ensure a salt-free root zone, evaporation from the groundwater must be prevented thus keeping the groundwater table below the depth that will cause rapid soil salinization. Provision of adequate drainage measures is the only way to control the groundwater table. Subsurface drainage problems may also arise due to the presence, at some soil depth, of a clay barrier, a hardpan, bed rock, or even a subsoil textural change.

     

    i. Surface drainage - In surface drainage, ditches are provided so that excess water will run off before it enters the soil. However the water intake rates of soils should be kept as high as possible so that water which could be stored will not be drained off. Field ditches empty into collecting ditches built to follow a natural water course. A natural grade or fall is needed to carry the water away from the area to be drained. The location of areas needing surface drainage can be determined by observing where water is standing on the ground after heavy rain. Field ditches and collection or outlet ditches should be large enough to remove at least 5 cm of water in 24 hours from a level to a gently sloping land. The capacity of a drainage system should be based on the amount and frequency of heavy rains. How quickly water runs into ditches depends on the rate of rainfall, land slope and the condition of the soil surface including the plant cover. The area that a ditch can satisfactorily drain depends on how quickly water runs into the ditch, the size of the ditch, its grade or slope and its irregularity. The latter is measured by the roughness and the contents of debris and growing vegetation in the ditch. In relatively level areas (slope < 0.2%) a collecting ditch may be installed along one side and shallow v-shaped field ditches constructed to discharge into this collecting ditch. Field ditches used to discharge water into collecting ditches should be laid out parallel to each other 20 to 60 m apart. They should be 30 to 45 cm deep depending upon the depth of the collecting ditch. Care should be taken to avoid sharp curves in the ditches to lessen erosion of the banks.

    ii. Subsurface drainage - If the natural subsurface drainage is insufficient to carry the excess water and dissolved salts away from an area without the groundwater table rising to a point where root aeration is affected adversely and the groundwater contributes appreciably to soil salinization, it may be necessary to install an artificial drainage system for the control of the groundwater table at a specified safe depth. The principal types of drainage systems may consist of horizontal relief drains such as open ditches, buried tiles or perforated pipes or in some cases pumped drainage wells (Plate 5).

     

    a. Open ditches:  Open drainage ditches are advantageous for removing large volumes of either surface or subsoil water from land and for use where the water table is near the surface and the slope is too slight for proper installation of tile drains. Where subsurface tile drains are uneconomic or physically impossible, as in many heavy clay soils and where the topography is nearly flat, open drains may be the only practical means of draining the land. Open ditches also serve as outlets for tile drains where their depth is sufficient and other conditions are favourable. The chief disadvantage of open drains is that they occupy land that might otherwise be put to cultivation; open ditches across cultivated fields also obstruct farming operations and are a danger to the livestock and are more costly to maintain than the subsurface covered drains. Open drains become ineffective due to growth of weeds, collapse of banks resulting in partial filling with soil material, etc., and must be periodically cleaned.

    b. Mole drains:  these are channels left by a bullet shaped device pulled through the soil, they have been used successfully for shallow subsurface drainage of heavy clay soils in many, relatively humid, parts of Europe but have been found impractical with soils of coarser texture. Mole drains are generally cheaper to install than tile or plastic tubings but may last only for two or three years. In addition to being temporary, mole drains are generally shallow and have not been used extensively where salinity build up from the groundwater table is a major problem.

    c. Other subsurface drains:  These include any type of buried conduit with open joints or perforations that collect and convey excess water from the soil. The conduits may be made from clay, concrete, plastic or other synthetic material but clay and concrete tiles have been the most widely used. Clay tiles are generally manufactured in 30 and 60 cm lengths and have an inside diameter of 10 to 25 cm. They are made from surface clay or shale, which is pulverized, extruded through a die, dried and then burnt in a kiln. Clay tiles are not affected by acid or sodic soils but those made from surface clay or poorly burnt tiles are subject to deterioration by freezing and thawing action. Good quality clay tiles have been found to last indefinitely in the soil. Concrete tiles are made from sand and gravel aggregate and steam or water-cured to obtain the desired strength. Concrete tiles are resistant to freezing and thawing but may be subject to deterioration in acid and sodic soils. For such soils the tiles should be made with cement having a special chemical composition. Water enters the tiles at the butt joints or spaces between adjacent sections. Both clay and concrete tiles may have fitted ends and be perforated for easier entry of water. All drain tiles should meet standard specifications.

    source:

    FAO website for soil salination.

    Managing Saline Soils by Colorado State University.

     

     

  2. Improvement of a saline soil implies the reduction of the salt concentration of the soil to a level that is not harmful to the crops.

    1 Comment

  4. NOT EASY ANSWER

    Hello your question need a complete evaluation of real problem, with only a picture is dificult to can decide the best way,

    most important is that to clean a soil and maintenance is needed a group of tecniques. 

    I think you can find information in the page of USDA, visit www.ars.usda.gov/main/main.htm and check for salinity soils, you can read interesting information.

    regards from Spain

    1 Comment

  7. You may avoid use of any chemicals whatsoever for at least 2 years - use manure like cow dung instead. Proper crop rotation during this period will help solve the problem.

  8. Out of Earth

    Junejo, there is a novel idea in the book, 'Out of the Earth' by Louis Bromfield.

    He dug a water hole in the saline area, dropped the salty water into it, planted it with willows, and grew fish in it. This kept the surrounding area clear and provided a new industry. Nowadays, you would look at floating vegetables on the water, keeping ducks or other poultry in rotation and planting deep rooted plants to bring down the water table. The past century of monoculture shallow rooted plants, and chemical only fertilising, is creating this sort of problem everywhere.

    1 Comment

  11. Marine water intrusion, excess use of water, water logging, excess use of chemical fertilizers are some of the causes of salinity. Hence the solutions lie in removing these causes. Better drainage, careful use of water, use of limited organic fertilizers etc may be the solutions.

    1 Comment

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  13. Addressing salinity problem of the soil

    The intrusion of seawater/brackish water inland is a problem all over the world  for various reasons such as sea level raising etc The best way to address the problem is to create a barrier between the land and sea and then leach the soil with fresh water and pump out the leached brackish solution and subject to reverse osmosis and pump back the fresh water and discharge the saline water back into the sea or allow it to evaporate in a separate area.When evaporating the saline water ,make sure the water does not percolate into the soil again by using a polyethene sheet so that saline water will be evaporated leaving salt behind.This process has to be continued for weeks or months till the ground water becomes normal.

    1 Comment

  14. Treat this as a regional problem

    Salinity occurs in low lying areas with saline groundwater table.  These low lying areas are basically discharge zones for the surrounding areas.  So, better irrigation management in the region to avoid excessive percolation is essential.  Then find ways to accelerate water in smallest possible area, and explore of these isolated areas can produce economic outputs - so, the solutions minimize negative externality and financially viable.  

    1 Comment

  17. We formulated a special product for Sodium issues in water or soils, it is Sodium Blocker. It is a clear liquid that can be injected into irrigation by fertigation or spray applied. It will release the sodium bound by cation bond in the soil or clay and flush it down way from the plant or crop. It is used across the western US and we successfully used it to restore rice fields the next year after the tsunami covered then with sea water in 2005. If you email me I will send you case studies. mc@turffeeding.com Michael

  18. Conducting reclamation operations necessary before planting by immersing the ground water quality alone several times to reduce the salinity of the soil to the appropriate border. Whatever was salty soil can be planted where tomatoes, cucumbers and pepper without problems

  19. Dear Mr. Bashir In pakistan extensive reserach has been undertaken to control salinity and to reclaim salt affected soils. Many Projects have been carried out. So I assume that there is a wealth of knowledge and experience available in Pakistan to solve these problems.(WAPDA for instance) The essence is as other commenters have mentioned: Leaching of the soil with water and installing and a drainage system to evacuate the salinsed drainage effluent out of the area. The left bank outfall drain has been specifically constructed to evacuate the drainage effluent towards the sea. Chemicals (gypsum) can be a help (but no solution) to combat the possible alkalinity of the soil. There is unfortunately no easy and cheap solution to control salinityt in an large area. If you do it lfield wise you will send the salinity toward the neighbours, not a vary cheelfull solution either.

  22. Treatment of Saline Soils

    Saline soils cannot be reclaimed by chemical amendments, conditioners or fertilizers. A field can only be reclaimed by removing salts from the plant root zone. In some cases, selecting salt-tolerant crops may be needed in addition to managing soils.

    There are three ways to manage saline soils. First, salts can be moved below the root zone by applying more water than the plant needs. This method is called the leaching requirement method. The second method, where soil moisture conditions dictate, combines the leaching requirement method with artificial drainage. Third, salts can be moved away from the root zone to locations in the soil, other than below the root zone, where they are not harmful. This third method is called managed accumulation.

    For Details visit this link http://www.ext.colostate.edu/pubs/crops/00503.html