Saline And Sodic Soils

1. 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

2. Saline and Sodic Soils
•Salt Affected Soils
–Common salt ions
•Ca
2+
•Mg
2+
•Na
+
•Cl
-
•SO
4
2-
•HCO
3
-
•CO
3
2-

3. Saline and Sodic Soils
•Suelos afectados por sales
ClasificaciónConductivid
ad
(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

4. Saline and Sodic Soils
•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

5. 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 SALINO
Higher
Salt
Solución del suelo
Membrana Célula
radical

6. Saline and Sodic Soils
•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

7. 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

8. 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 + K
2O within 2” of corn seed at
planting
•Recommendation is no more than 15 lb/A
of N + K
2O directly with corn seed at
planting
–Primarily germination and early growth
problems
–Usually temporary under our humid
conditions

9. Saline and Sodic Soils
•Sodic Soil
–High sodium > 15% CEC
•ESP = Exchangeable Sodium Percentage
–High pH > 8.5
•pH of Na
2CO
3in 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

10. Saline and Sodic Soils
•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

11. Saline and Sodic Soils
•Sodic Soil
–Flocculation Van der Waals Attraction
–Short range attraction
Ca
2+
Ca
2+
Na
+
Flocculated
Small hydrated
ionic radius
Dispersed
Large hydrated
ionic radius

12. Saline and Sodic Soils
•Sodic Soil
Flocculated
Aggregation
Dispersed
Sealing

13. Saline and Sodic Soils
•Sodic Soil –Reduced Hydraulic Conductivity
0 10 20 30 40
ESP %
Hydraulic
Conductivity

14. Saline and Sodic Soils
•Sodic Soil -Management
–Leach with low Na
+
, salty water to exchange
Ca
2+
for Na
+
–Gypsum often added to create salty, low
sodium water
Na-Soil + CaSO
4→ Ca-Soil + Na
+
+ SO
4
2-
–Leach with clean water to flush out Na
+
& SO
4
2-
–Very difficult because you can’t get water into
the soil to do the leaching!!!

15. Saline and Sodic Soils
•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
+
] / √([Ca
2+
] + [Mg
2+
])/2
ESR = 0.015 SAR
SAR > 13 will give ESP > 15%
•Figure 3.25 Textbook Classification of Irrigation Water

16. Saline and Sodic Soils
•Sodic Soil -Management
–Use of Gypsum
Na-Soil + CaSO
4→ Ca-Soil + Na
+
+ SO
4
2-
•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 Ca
2+
to
exchange with Na
+
(Example in Textbook)

17. Saline and Sodic Soils
•Saline-Sodic Soil
–High salt andhigh sodium
–High sodium > 15% CEC
•ESP = Exchangeable Sodium Percentage
–High salt content in soil solution
•EC > 4 mmhos/cm
–pH < 8.5

18. Saline and Sodic Soils
•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 !!!

19. 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

20. Summary of Saline & Sodic Soils
Figure 3.21 in Textbook
Electrical Conductivity (mmhos/cm)