Saline And Sodic Soils

Saline and Sodic Soils• Salt Affected Soils

– Occur when rainfall is not sufficient for adequate leaching of salts

– Usually less than 20 "/yr precipitation– Common in arid regions

• Western US• Irrigated agriculture

– Not common in PA• Heavy salt application for ice melting• Land application of high salt waste materials

– Can ruin soils for agriculture

Saline and Sodic Soils

• Salt Affected Soils – Common salt ions

• Ca2+ • Mg2+

• Na+

• Cl-

• SO42-

• HCO3-

• CO32-

Saline and Sodic Soils• Suelos afectados por sales

Clasificación Conductividad

(mmhos/cm)

pH % Na intercble

Condiciones

físicas

SALINE > 4 < 8.5 < 15 Normal

SODICO < 4 > 8.5 > 15 Pobre

SALINO/SODICO >4 < 8.5 > 15 Normal

Conductivity (EC) - Electrical conductivity of the soil water. Soluble salt ions will carry an electrical current. Therefore the higher the salt level the higher the conductivity.

EC x 10 ≈ Soluble cations (meq/L)

% Exch. Na - % saturation of Na on the soil CEC


• Saline Soil– High salt content in soil solution– “White Alkali” soils – salt accumulation at soil

surface– EC > 4 mmhos/cm = 40 meq/L– Salts raise the osmotic potential of the soil

solution reduces available soil water– Plants have to use more energy to get the

water they need

Saline and Sodic Soils• Saline Soil – Osmotic Effect

– El agua se moverá desde donde la concentración de sal es baja hacia donde es alta

Raíz

Membrana Célula radical

ALTA Sal

BAJA Sal

Suelo Normal

Root Soil Solution

High Salt High Salt Suelo SALINOHigher

Salt

Solución del suelo

Membrana Célula radical


• Saline Soil – Effects on plants– Stunted growth– Wilting– Bluish-green color– Necrosis of leaf tips– Drought stress symptoms– Specific toxicities eg. Boron– Plant species vary in salt tolerance

• See table 3.19 in Textbook

Saline and Sodic Soils• Saline Soil – Management

– Add enough irrigation water to leach salts below the root zone

– Preferably drain the salty water away– Salts within 1m of the surface can move back into the

rooting zone with evaporation– Quantity of irrigation water required:

• Quality of irrigation water (Good quality = low salt)• Quality of drainage water• Soil water holding capacity• Rooting depth• Salt tolerance of plants

• Formulas available to calculate the amount of water needed– .5 m water /m of soil will remove ~ 50% of salts– 1 m water / m soil will remove ~ 80% of salts

Saline and Sodic Soils• Salt injury from fertilizer

– High salt levels when high rates of fertilizer or manure applied

– More serious when banded• Recommendation is no more than 70 lb/A

of N + K2O within 2” of corn seed at planting

• Recommendation is no more than 15 lb/A of N + K2O directly with corn seed at planting

– Primarily germination and early growth problems

– Usually temporary under our humid conditions


• Sodic Soil– High sodium > 15% CEC

• ESP = Exchangeable Sodium Percentage

– High pH > 8.5• pH of Na2CO3 in water is 9.5

– “Black alkali” soils – dissolved OM and salt accumulation at the soil surface

– Main problem is the effect of sodium on flocculation and aggregation of soil particles


• Sodic Soil– Sodium causes the soil particles to disperse– No aggregation of soil particles– Individual clay particles clog soil pores– Poor soil physical properties

• Very difficult for water and air movement and root penetration

– Plants cannot grow in sodic soils

Saline and Sodic Soils• Sodic Soil

– Flocculation Van der Waals Attraction– Short range attraction

Ca2+

Ca2+

Na+

Flocculated

Small hydrated ionic radius

Dispersed

Large hydrated ionic radius

Saline and Sodic Soils• Sodic Soil

Flocculated

Aggregation

Dispersed

Sealing

Saline and Sodic Soils• Sodic Soil –Reduced Hydraulic Conductivity

0 10 20 30 40

ESP %

Hyd

raul

ic

Con

duct

ivity


• Sodic Soil - Management– Leach with low Na+, salty water to exchange

Ca2+ for Na+

– Gypsum often added to create salty, low sodium water

Na-Soil + CaSO4 → Ca-Soil + Na+ + SO42-

– Leach with clean water to flush out Na+ & SO42-

– Very difficult because you can’t get water into

the soil to do the leaching!!!


• Sodic Soil - Management– Reduce ESP < 15 % of CEC– Use low sodium irrigation water

• Sodium Adsorption Ratio (SAR)• Ion concentrations in irrigation water (meq/L)

SAR = [Na+] / √ ([Ca2+] + [Mg2+])/2

ESR = 0.015 SAR

SAR > 13 will give ESP > 15%

• Figure 3.25 Textbook Classification of Irrigation Water

Saline and Sodic Soils• Sodic Soil - Management

– Use of Gypsum

Na-Soil + CaSO4 → Ca-Soil + Na+ + SO42-

• Provides Ca but doesn’t increase pH like limestone• Perception that adding Gypsum will always

improve soil structure• True for sodic and saline/sodic soil but not in most

other cases if Ca is adequate and Na is low• In acid soils we don’t have Na and we get plenty of

Ca from limestone• Amount of Gypsum to provide equivalent Ca2+ to

exchange with Na+ (Example in Textbook)


• Saline-Sodic Soil– High salt and high sodium– High sodium > 15% CEC

• ESP = Exchangeable Sodium Percentage

– High salt content in soil solution• EC > 4 mmhos/cm

– pH < 8.5


• Saline-Sodic Soil– As long as the salts remain high these soils

will remain floculated– Don’t have the serious physical properties

that sodic soils have– Problems similar to saline soils– Can be come sodic very easily with improper

management !!!

Saline and Sodic Soils• Saline-Sodic Soil Management

– Similar to sodic soil management• Leach with low sodium, saline water to exchange Na+

• This creates a saline soil• Then manage as a saline soil eg. Leach out the salts

with clean water

– Easier to manage than sodic soil– Very critical to use a high salt, low sodium water

or it will become sodic

Summary of Saline & Sodic Soils

Figure 3.21 in Textbook

Electrical Conductivity (mmhos/cm)

Technology

Saline And Sodic Soils