If your soil has a high salinity content, the plants

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1 E Maagig Soil Saliity Toy Provi ad J.L. Pitt* If your soil has a high saliity cotet, the plats growig there will ot be as vigorous as they would be i ormal soils. Seeds will germiate poorly, if at all, ad the plats will grow slowly or become stuted. If the saliity cocetratio is high eough, the plats will wilt ad die, o matter how much you water them. Routie soil testig ca idetify your soil s saliity levels ad suggest measures you ca take to correct the specific saliity problem i your soil. Saliity ad salt The terms salt ad saliity are ofte used iterchageably, ad sometimes icorrectly. A salt is simply a iorgaic mieral that ca dissolve i water. May people associate salt with sodium chloride commo table salt. I reality, the salts that affect both surface water ad groudwater ofte are a combiatio of sodium, calcium, potassium, magesium, chlorides, itrates, sulfates, bicarboates ad carboates (Table 1). Table 1. Typical salts foud i irrigatio water. Commo Chemical Chemical Name Name Formula Table salt Sodium chloride NaCl Glauberís salt Sodium sulfate Na 2 SO 4 Bakig soda Sodium bicarboate NaHCO 3 Epsom salt Magesium sulfate MgSO 4 Gypsum Calcium sulfate CaSO 4 2H 2 O Street salt Calcium chloride CaCl 2 2H 2 O Muriate of potash Potassium chloride KCl Muriate of sulfate Potassium sulfate K2SO 4 * Professor ad Extesio Soil Chemist, Extesio Program Specialist; The Texas A&M Uiversity System. These salts ofte origiate from the earth s crust. They also ca result from weatherig, i which small amouts of rock ad other deposits are dissolved over time ad carried away by water. This slow weatherig may cause salts to accumulate i both surface ad udergroud waters. The surface ruoff of these dissolved salts is what gives the salt cotet to our oceas ad lakes. Fertilizers ad orgaic amedmets also add salts to the soil. Effects of salts o plats As soils become more salie, plats become uable to draw as much water from the soil. This is because the plat roots cotai varyig cocetratios of ios (salts) that create a atural flow of water from the soil ito the plat roots. As the level of saliity i the soil ears that of the roots, however, water becomes less ad less likely to eter the root. I fact, whe the soil saliity levels are high eough, the water i the roots is pulled back ito the soil. The plats become uable to take i eough water to grow. Each plat species aturally cotais varyig levels of root salts. This is why some plats ca cotiue to thrive whe others have died. If the saliity cocetratio i the soil is high eough, the plat will wilt ad die, regardless of the amout of water applied. Figure 1 shows how the various salt cocetratios affect the movemet of water from the soil to plats. Salt buildup Saliity is of greatest cocer i soils that are: Irrigated with water high i salts; Poorly draied, allowig for too much evaporatio from the soil surface; Naturally high i salts because very little salt leaches out; I areas where the water table (the level or depth to free-flowable water i the soil) is shallow; or I seepage zoes, which are areas where water from other locatios (ormally up slope) seep out. The major source of saliity problems is usually irrigatio water. This is a gradual process the salts must accumulate over time before ay effects are

2 Figure 1. Icreased salts i root zoe ca result i decreased water uptake by plat. see. Fortuately, plats take up may salts i the form of utriets. But whe more salt is added to the soil tha is removed, the plats will evetually be affected. I some soils, irrigatio ad raiwater move through the soil to leach out the saliity. Leachig occurs whe water moves materials (such as salts or orgaic materials) dowward through the soil. Several soil factors ca ihibit leachig: a high clay cotet; compactio; a very high sodium cotet; or a high water table. Salt problems occur whe water remais ear the surface ad evaporates, ad whe salts are ot dissolved ad carried below the root zoe. Soils aturally high i soluble salts are usually foud i arid or semi-arid regios, where salts ofte accumulate because there is ot eough raifall to dissolve them ad leach them out of the root zoe. Salt spray ear coastlies ca also cause salts to build up i the soil. I areas with shallow water tables, water cotaiig dissolved salts may move upward ito the rootig zoe. This occurs by capillary actio (similar to the way a wick works), where evaporatio serves as the suctio of water up through the soil (Fig. 2). Water moves the farthest through fier clay ad clay loam soils; it moves less i medium-textured soils (loams); ad least i coarser, sady soils. Soil testig To determie the type of problem i your soil, collect a soil sample ad have it tested. The best idicator of the extet of a salt problem is a detailed saliity aalysis, i which water is extracted from a paste. This test measures the ph, electrical coductivity (EC) ad water-soluble levels of the soil. EC is a measure of the amout of dissolved salts i the paste of soil ad water. The Texas Agricultural Extesio Service coducts several types of soil tests, icludig detailed saliity aalyses. For more iformatio o soil testig, see Extesio publicatio L-1793, Testig Your Soil: How to Collect ad Sed Samples or check the Web site of the Soil, Water, ad Forage Testig Laboratory at The laboratory s phoe umber is (979) Salt-affected soils Salt buildup ca result i three types of soils: salie, salie-sodic ad sodic. Salie soils are the easiest to correct; sodic soils are more difficult. Each type of soil has uique properties that require special maagemet. 2

3 Salie-sodic soils typically have a EC of less tha 4 mmho cm -1, ad the ph is geerally below 8.5. The exchageable sodium percetage is more tha 15 percet of the catio exchage capacity (CEC). CEC is a measure of the soil s capacity to hold catios, amely, calcium, magesium, potassium, sodium, hydroge ad alumium. The higher the CEC, the more problematic the removal ad remediatio of the salt problem. Water moves through these soils much as it does i salie soils, although the steps for correctig saliesodic soil are differet. Simply leachig the salts from this soil will covert it from salie-sodic to sodic soils. Figure 2. Leachig is the process of addig sufficiet water to the soil to dissolve salts ad carry them out of the root zoe. a. Whe the salt cocetratio i the soil is less tha that i the plat, water moves from the soil ito the plat. b. Whe the salt cocetratio i the soil is equal to that of the plat, there is o et movemet of water. c. Whe the salt cocetratio i the soil is greater tha that of the plat, water moves from the plat ito the soil. Salie soils Salie soils cotai eough soluble salts to ijure plats. They are characterized by white or light brow crusts o the surface. Salie soils usually have a EC of more tha 4 mmho cm -1. Salts geerally foud i salie soils iclude NaCl (table salt), CaCl 2, gypsum (CaSO 4 ), magesium sulfate, potassium chloride ad sodium sulfate. The calcium ad magesium salts are at a high eough cocetratio to offset the egative soil effects of the sodium salts. The ph of salie soils is geerally below 8.5. The ormal desired rage is 6.0 to 7.0, but may Texas soils are aturally 7.5 to 8.3. Leachig the salts from these soils does ot icrease the ph of salie soils. Salie-sodic soils Salie-sodic soils are like salie soils, except that they have sigificatly higher cocetratios of sodium salts relative to calcium ad magesium salts. Sodic soils Sodic soils are low i soluble salts but relatively high i exchageable sodium. Sodic soils are usuitable for may plats because of their high sodium cocetratio, which may cause plat rootig problems, ad because of their high ph, which geerally rages from 8.5 to These high sodium levels disrupt both the chemical ad physical compositio of soil clays. As a result, the soil surface has low permeability to air, rai ad irrigatio water. The soil is sticky whe wet but forms hard clods ad crusts upo dryig. This pheomeo may ot occur i very sady soils because they lack clay cotet. Salt problems Whe salts accumulate i soils, problems arise for two mai reasos: the soil becomes less permeable, ad the salt damages or kills the plats. The first problem is associated with the soil structure. I sodic soils, high levels of exchageable sodium cause the idividual sad, silt ad clay particles to be separated ad ot clumped together ito larger particles. This dispersio makes the soil tight ad impervious, so that it allows little air, rai or irrigatio water to permeate ito the soil. Therefore, the plats may ot receive eough moisture ad oxyge to grow. Salts may accumulate o the soil surface because they caot leach out of the root zoe. Plats ca also be damaged by salt effects or toxicity. I salie ad salie-sodic soils, high cocetratios of soluble salts reduce the amout of available water for plats to use. High levels of sodium ca be toxic to certai plats. Also, the very high soil ph i high-salt soils greatly chages the utriets available to the plats. These 3

4 high ph levels chage the ioic form of may plat utriets to forms that make them uavailable to plats. Correctig salt-affected soils Salt-affected soils ca be corrected by: Improvig draiage Leachig Reducig evaporatio Applyig chemical treatmets A combiatio of these methods Improvig draiage: I soils with poor draiage, deep tillage ca be used to break up the soil surface as well as claypas ad hardpas, which are layers of clay or other hard soils that restrict the dowward flow of water. Tillig helps the water move dowward through the soil. While deep tillage will help temporarily, the parts of the soil ot permaetly broke up may reseal. Leachig: Leachig ca be used to reduce the salts i soils. You must add eough low-salt water to the soil surface to dissolve the salts ad move them below the root zoe. The water must be relatively free of salts (1,500-2,000 ppm total salts), particularly sodium salts. A water test ca determie the level of salts i your water. Leachig works well o salie soils that have good structure ad iteral draiage. To leach a highly salie soil, you may eed to apply as much as 48 acreiches of water. A acre-ich is the volume of water that would cover 1 square acre to a depth of 1 ich (27,152 gallos). Testig is ofte eeded to determie how much water is eeded to correct a particular soil. The testig laboratory ca advise o how much water to add. After a applicatio, the soil ofte must be retested to determie whether eough salts were leached out. Highly salie soils should be leached usig several applicatios, so that the water ca drai well. Here agai, draiage ca be a problem. If the water caot ifiltrate the soil, the salts caot be dissolved ad leached out of the soil. Reducig evaporatio: Applyig residue or mulch to the soil ca help lower evaporatio rates. Chemical treatmets: Before leachig salie-sodic ad sodic soils, you must first treat them with chemicals, to reduce the exchageable sodium cotet. To remove or exchage with the sodium, add calcium i a soluble form such as gypsum. Agai, the laboratory aalysis ca determie how much calcium to add. After the calcium treatmet, the sodium ca the be leached through the soil alog with the other soluble salts. Gypsum is the most commo amedmet used to correct salie-sodic or sodic soils that have o calcium source such as gypsum or free carboates. These are available at garde ceters ad agricultural supply stores. Aother amedmet, calcium chloride, is used i some places, but it is seldom available i most areas. May soils i the souther ad wester two-thirds parts of Texas cotai sigificat cocetratios of free limestoe, which cotais calcium carboate. Ufortuately, these calcium sources do ot dissolve i soils with high ph ad therefore caot help lower sodium levels. If your soil cotais free carboates, you ca add acids to it to form gypsum, which will react with the soil to remove the exchageable sodium. Add sulfuric acid, sulfur, iro sulfates ad alumium sulfate, which will react i the soil to produce acid. The acid will the react with the calcium carboates (limestoe) to form calcium sulfate (gypsum), water ad carbo dioxide. The acidity may also displace some of the sodium. Table 2 lists typical amedmets used to correct salt-affected soils. Although all of these amedmets work, to use them you must kow the amout of reactive limestoe preset. I geeral, gypsum is the safest ad most effective material. Steps for treatig sodic ad salie-sodic soils Correctig salie-sodic ad sodic soils is a slow process that must be carried out i steps: 1. Treat the surface first, the cotiue to the lower depths. 2. Apply a amedmet to the soil surface ad disk it i. 3. Add 10 to 12 iches of water. As whe correctig salie soils, you must add eough water to dissolve as well as maitai the calcium cocetratios i solutio ad to move the salts ad sodium through the soil. However, do ot add so much water that it remais poded o the soil surface for exteded periods. Geerally, this process must be repeated over time. A good goal is to remove the sodium to a miimum depth of 3 to 4 feet. Test the soil periodically to pipoit potetial saliity problems ad to measure your progress i correctig salt-affected soils. 4

5 Table 2. Typical soil amedmets for correctig salie ad salie-sodic soils 1 Approximate No. Pouds to Supply 1,000 Pouds Amedmet Chemical Formula Purity, % 2 of Soluble Calcium 3 Gypsum CaSO 4 2H 2 O 100 4,300 Calcium chloride CaCl 2 2H 2 O 100 3,700 Sulfur 4 S Sulfuric acid 4 H2 SO ,600 Iro sulfate 4 FeSO 4 7H 2 O 100 6,950 Alumium sulfate 4 Al(SO 4 )318H 2 O 100 5,550 Lime-sulfur solutio 4,5 Calcium polysulfide 24 3,350 1 From USDA Agriculture Iformatio Bulleti No (1) 2 With purities less tha these, additioal material will eed to be supplied. 3 Assumes free carboates preset to react with the amedmets that cotai o calcium. 4 Sulfur amedmets are oly used i soils that cotai free calcium carboates. 5 Expressed as sulfur cotet. The amout of amedmet you eed to correct salie-sodic ad sodic soils is based o the amout of sodium i the soil. Several other factors also ifluece the amout applied: the leachig rate, the solubility ad reactio rates of the amedmets, ad the coversio of free carboates to gypsum. If you take steps early, correctig the soil will be easier ad less expesive, ad it will have less egative impact o soils ad plats.