Circular1019Leticia S. Sonon,Uttam Saha, andDavid E. KisselAgricultural and Environmental Services Laboratories.The University of Georgia Agricultural and Environmental Services Laboratories offer soil salinity testing to helpfarmers and the general public diagnose and manage problems associated with soil salinity.
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By definition, a salinesoil contains excess soluble salts that reduce the growth of most crops or ornamental plants. These soluble saltscontain cations such as sodium (Na +), potassium (K +), calcium (Ca 2+) and magnesium (Mg 2+) along with anions chloride (Cl -), sulfate (SO 4 2-), nitrate (NO 3 -), bicarbonate (HCO 3 -) and carbonate (CO 3 2-). Left: Soil with good structure(non-sodic soil).Right: Soil with poor and densestructure (sodic soil).Soil salinity is caused by several factors. Soils may become saline as aresult of land use, including the use of irrigation water with high levelsof salt. Seawater is also a source of salts in low-lying areas along the coastthrough tidal estuaries or when rainfall in coastal regions mixes with seaspray.
Saltwater intrusion into freshwater aquifers may occur when wellsare close to the coast and water is pumped to the surface for various purposes,including irrigation. Irrigating from salt-impacted wells or salineindustrial water may lead to the formation of saline soils.Soil sodicity, on the other hand, is caused by high sodium levels in soilsat concentrations greater than 15 percent of the cation exchange capacity.
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Sodic soils tend to have poor structurewith unfavorable physical properties such as poor water infiltration and air exchange, which can reduce plantgrowth. Effects of Salinity on Plant GrowthSalinity reduces water availability for plant use. High salt levels hinder water absorption, inducing physiologicaldrought in the plant.
Place 1 to 3 teaspoons of soil in a clean plastic cup and remove sticks, stones, and debris. Fill the cup with distilled water to match the same level as the soil sample. Agitate the soil vigorously, by stirring or swirling, and then let the solution rest for 30 minutes. So what is the cause of this phenomenon and what can be done to prevent or cure it? Efflorescence is a crystaline, salty deposit that occurs on the surfaces of. In contact with salt bearing water or soil, this can in turn transfer the salt to the.
The soil may contain adequate water, but plant roots are unable to absorb the water due tounfavorable osmotic pressure. This is referred to as the osmotic or water-deficit effect of salinity.
Plants are generallymost sensitive to salinity during germination and early growth.The second effect of salinity is shown when excessive amounts of salt enter the plant in the transpiration streamand injure leaf cells, which further reduces growth. This is called the salt-specific or ion-excess effect of salinity(Greenway and Munns, 1980).
Symptoms may include restricted root growth, marginal or leaf tip burning/browning, inhibited flowering, reduced vigor and reduced crop yields. Visual Diagnosis of Salt-Affected SoilsAccumulation of salts can result in three soil conditions: saline, saline-sodic and sodic soils. Each of these soilconditions has distinct characteristics that can be observed in the field, which are useful for diagnosing theproblem. Completely white soils are saline, soils with a brownish-black crust are sodic, and grey-colored soils aregenerally saline-sodic.
The following physical observations/symptoms may be helpful in diagnosing salt-relatedsoil problems: ProblemSymptomsSalineWhite crust on soil surface. Water-stressed plants. Leaf tip burn.SodicPoor drainage.
Black powdery residue on soil surface.Saline-SodicGrey-colored soil. Plants showing water stress.Source: Waskom et al., 2010.
Diagnosing saline and sodic soil problems. Colorado State University Extension Fact Sheet # 0.521Soil Salinity MeasurementsProblems due to soil salinity and sodicity in soil are commonly evaluated by laboratory testing. The followinglaboratory measurements are typically used to determine the extent of these problems:1. Electrical Conductivity (EC) — Measures the ability of the soil solution to conduct electricity and is expressedin decisiemens per meter (dS/m, which is equivalent to mmhos/cm). Because pure water is a poorconductor of electricity, increases in soluble salts result in proportional increases in the solution EC. Thestandard procedure for salinity testing is to measure EC of a solution extracted from a soil wetted to a 'saturationpaste.' According to U.S.
Salinity Laboratory Staff (1954), a saline soil has an EC of the saturated pasteextract of more than 4 dS/m, a value that corresponds to approximately 40 mmol salts per liter. Crops varyin their tolerance to salinity and some may be adversely affected at ECs less than 4 dS/m. Salt tolerances areknown for common crops. For example, peach is sensitive, whereas cotton is more salt tolerant (Maas, 1990).Beets and asparagus are very tolerant of salinity.2. Total Soluble Salts (TSS) — Refers to the total amount of soluble salts in a soil-saturated paste extract expressedin parts per million or milligrams per liter (ppm or mg/L). A linear relationship exists between TSSand EC within a certain range that can be useful to closely estimate soluble salts in a soil solution or extract.The ratio of TSS to EC of various salt solutions ranges from 550 to 700 ppm per dS/m. Sodium chloride, themost common salt, has a TSS of 640 ppm per dS/m.
So if EC is known, TSS can be estimated using the formulabelow: TSS (mg/L or ppm) = EC (mmhos/cm or dS/m) x 6403. Sodium Adsorption Ratio (SAR) — A widely accepted index for characterizing soil sodicity, which describesthe proportion of sodium to calcium and magnesium in soil solution. The formula to calculate SAR is givenbelow, with concentrations expressed in milliequivalents per liter (meq/L) analyzed from a saturated pastesoil extract. When SAR is greater than 13, the soil is called a sodic soil.
Excess sodium in sodic soils causes soil particlesto repel each other, preventing the formation of soil aggregates. This results in a very tight soil structure withpoor water infiltration, poor aeration and surface crusting, which makes tillage difficult and restricts seedlingemergence and root growth (Munshower, 1994; Seelig, 2000; Horneck et al., 2007).4. Exchangeable Sodium Percentage (ESP) — Another index that characterizes soil sodicity. As noted above,excess sodium causes poor water movement and poor aeration. By definition, sodic soil has an ESP greaterthan 15 (US Salinity Lab Staff, 1954). ESP is the sodium adsorbed on soil particles as a percentage of the CationExchange Capacity (CEC).
It is calculated as: ESP = Na 2+x 100CECCEC is often estimated as the sum of the major exchangeable cations, including hydrogen. Both cations andCEC are expressed as meq/100g. Preparing saturated pastes.The following parameters are included in the comprehensive soil salinity test:1. Saturated Paste Extract. Calcium (Ca 2+).
Magnesium (Mg 2+). Potassium (K +). Chloride (Cl -).
Sodium (Na +). Nitrate-nitrogen (NO 3-N). Sulfate (SO 4 2-). pH. Electrical Conductivity (EC). Total Soluble Salts (TSS). Sodium Adsorption Ratio (SAR)2.
NH 4OAc Extract. Calcium (Ca 2+). Magnesium (Mg 2+). Sodium (Na +).
Potassium (K +). Exchangeable Sodium Percentage (ESP)The general interpretation of data on electrical conductivity and exchangeable sodium percentage from saturatedpaste extracts are given below. Interpretation of electrical conductivity (EC) from saturated paste extract.Electrical conductivity(mmhos/cm)Salt RankInterpretation0-2LowVery little chance of injury on all plants.2-4ModerateSensitive plants and seedlings of others may show injury.4-8HighMost non-salt tolerant plants will show injury; salt-sensitive plants willshow severe injury.8-16ExcessiveSalt-tolerant plants will grow; most others show severe injury.16+Very ExcessiveVery few plants will tolerate and grow.Source: Lamond, R. Management of saline and sodic soils. Kansas State University, Department of Agronomy MF-1022.Interpretation of exchangeable sodium percentage (ESP) from saturated paste extract.ESPRankInterpretation0-10LowNo adverse effect on soil is likely.10+ExcessiveSoil dispersion resulting in poor soil physical condition and poor plant growth are likely.Source: Lamond, R. Management of saline and sodic soils.
Kansas State University, Department of Agronomy MF-1022.Reclaiming Salt-Affected SoilsAfter the kinds and amounts of salts in the soil have been determined by testing, the soil can be properly treated.Reclaiming a salt-affected soil involves leaching, chemical treatment or a combination of both. LeachingApplication of good quality irrigation water in the correct amounts will remove excess salts from soilsthat are well structured and have good internal drainage. Excess salts should be leached below the root zoneso that the EC of the soil solution becomes lower than the crop's critical threshold. The University of Georgiarecommends leaching techniques to remove salts from the root zone when EC is greater than 1.25 mmhos/cm ata soil-to-water ratio of 1:2.
The volume of low-salt water needed to dissolve and leach any large quantities of saltsfrom the soil is given below. A general rule of thumb is that 6 inches of water will remove about half of the salt,12 inches will remove 4/5, and 24 inches will remove 9/10.
Estimated leaching requirements to remove saltsVolume of salt-free waterReduction of salt content in soil6 inches50%12 inches80%24 inches90%For soils with poor drainage, it is recommended to break root-restrictive hardpans or clay pans by deep tillage toallow water to penetrate and leach the salts. It may be necessary to install tile drains to remove salt-laden drainagewater and move it below the root zone by rainfall or irrigation water. Chemical treatmentWhen a soil has an SAR value of above 13 (or ESP greater than 15), it contains excesssodium that makes it a sodic soil.
Excess sodium can cause soil dispersion, which prevents the formation of soilaggregates, resulting in surface sealing or crusting. Dispersion of the soil by excess sodium reduces water infiltrationand movement through the soil, and also causes poor aeration. Good aeration and water movement areboth essential to unrestricted growth of plant roots. To eliminate surface sealing, the soil should be treated withcalcium to remove sodium. One of the most commonly used calcium sources for correcting sodium-contaminatedsoil is gypsum (calcium sulfate, CaSO 4.2H 2O).
Gypsum is incorporated into the soil, followed by applicationof salt-free irrigation water. The amount of calcium to apply depends on the quantity of sodium in the soil. Roadde-icing salt or calcium chloride (CaCl 2) is also an option to provide calcium to soil, but it is more expensivethan gypsum.The table below provides the amount of gypsum needed to replace exchangeable sodium in the soil.
The soil testsodium values are determined from an ammonium acetate extraction at pH 7. Soil exchangeablesodiumAmount of Gypsum Needed aCaSO 4.2H 2Olbs/acreTons/acre-foot bTons/acre-6 inches clbs/1000 ft 2-1 footlbs/1000 ft 2-6 inches46092801381201841602302002760240Source: U.S. Salinity Laboratory Staff, 1954, with modifications.a The amounts of gypsum are given to the nearest 0.1 ton.b 1 acre-foot of soil weighs approximately 4,000,000 pounds.c 1 acre-6 inches of soil weighs approximately 2,000,000 pounds.Correcting a salt-affected soil involves identifying the kind and amount of salt, chemical treatment and leaching.When a salinity problem is identified, it is recommended that corrective steps be taken immediately. Prompt actionwill give a better chance of reclaiming the affected soil, be less expensive and pose less risk of plant damage.
ReferencesGreenway H., Munns R. Mechanisms of salt tolerance in nonhalophytes. Plant Physiol. 31:149-190.Horneck, D.S., Ellsworth, J.W., Hopkins, B.G., Sullivan, D.M., Stevens, R.G., 2007. Managing Salt-Affected Soils for CropProduction.
Oregon State University, University of Idaho, Washington State University.Lamond, R. Management of saline and sodic soils. Kansas State University, Department ofAgronomy MF-1022.Maas, E.V. Crop salt tolerance. In Agricultural Salinity Assessment and Management. Tanji (Ed) AmericanSociety of Civil Engineers.Munshower, F.F.
Practical Handbook of Disturbed Land Revegetation. Lewis Publisher, Boca Raton, FL.Seelig, B.D. Salinity and Sodicity in North Dakota Soils. North Dakota State University, Fargo, ND.US Salinity Laboratory Staff. Diagnosis and improvement of saline and alkali soils. USDA Agricultural HandbookNo. Government Printing Office.
Washington, DC.Waskom, R.M., T.A. Davis, and G.E. Diagnosing saline and sodic soil problems.
Colorado StateUniversity Extension Fact Sheet # 0.521.Status and Revision HistoryPublished on May 31, 2012Published with Full Review on Oct 05, 2015.
good planting soil image by tomcat2170 from Fotolia.com
Soil pH is the amount of acid or alkaline in a soil. Most plants require a neutral pH or a soil that is balanced. Typically a soil's pH can range from 4.0, which is extremely acid, up to 9.0, which is very alkaline. A balanced soil is 7.0, which is equivalent to pure water. The best way to test a soil's pH value is to conduct a soil test. Your local agricultural extension service offers these tests for little to no cost.
Conduct the soil test for the area you want to balance the pH level. Typically the soil is taken from a number of locations from around the field or garden site. The soil is thoroughly mixed, allowed to dry and a sample is sent to the extension service. Generally it takes up to 4 weeks to receive the test results back from the laboratory.
Read the test results and consult the extension service if any information is not clear. You can cause a larger problem by adding too much lime to reduce the acid level in the soil. In the same manner, you can also add too much nitrogen-based fertilizer to lower a high alkaline soil.
Broadcast the correct amount of the pH balancing agent over the soil. Generally this is described as pounds per acre. In a smaller garden plot, it will be described as pounds per 1,000 square feet. Agricultural lime will be added to reduce the acid level in a soil and raise the pH level. A nitrogen fertilizer, typically an ammonia base, will be used to lower a high pH level.
Use some type of cultivation method to work the balancing agent into the soil. A large field will require the use of a tractor that can pull a mechanical cultivator over the field. The tines of the cultivator will mix the agent into the soil. Use a roto tiller to work in small areas such as garden plots or flowerbeds. Generally the application of any balancing agent is performed in late winter to early spring prior to any planting of crops or plants.
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Allow the material, added to the location, to sit for one year. Take another soil test and wait for the results. Balancing the pH level in soil takes time. In some cases, it is part of a routine soil management program.
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