Oak Hill Case
Soil Chemical Problems
Water Deficits
Ion
Toxicities
SALT RELATED
PROBLEMS
Soil Permeability
Ion
Imbalances
Water Deficits
Ion
Toxicities
SALT RELATED
PROBLEMS
Soil Permeability
Ion
Imbalances
Water deficits reflect
salinity problems
from salt concentrations
Soil permeability reflects
sodicity problems
from sodium concentrations
Salinity
A measure of the salt
concentration of water
Common Salt Ions
Ca2+
K+
NO3-
Mg2+
Cl-
HCO3-
Na+
SO4
2-
CO32-
Salinity Measurement
• Measured as the electrical conductivity
of water (ECw)
• Expressed as decisiemens per meter
(dS/m); formerly as mmhos/cm.
sw vs ECe
- 0.36 bar
1.0 dS/m
- 0.72 bar
2.0 dS/m
- 1.44 bar
4.0 dS/m
- 2.16 bar
6.0 dS/m
Transpiration
High salt concentration
Salt-Induced Water Deficits
 WATER UPTAKE
 stomatal
opening
 cell-turgor
pressure
 cytokinin
synthesis
 cell-turgor
extensibility
 photosynthesis
respiration
 GROWTH
leaf wilting
 transpirational
cooling
DESICCATION
C1-S4
C2-S4
C3-S4
C1-S3
Sodium
Hazard
C4-S4
C2-S3
C1-S2
C3-S3
C2-S2
C4-S3
C3-S2
C1-S1
C2-S1
C4-S2
C3-S1
C4-S1
0.25
1
Class
0.75
2
3
Salinity Hazard
2.25
4
EC(dS/m)
at 25 oC
Sodicity
A measure of the sodium [Na+] concentration
in relation to the calcium [Ca+2] and
magnesium [Mg+2] concentrations of water
Sodicity Measurement
• Measured as the sodium absorption ratio of water
(SARw)
• Expressed as the ratio:
Na+/ ([Ca+2 + Mg+2]/2) 1/2
• Where the concentration of each ion is expressed
in milliequivalents per liter (meq/L)
Problem
With a water-quality report providing sodium,
calcium, and magnesium concentrations as 76,
146, and 39 mg/L, how do we express these in
meq/L?
Atomic Weights
Element
Calcium, Ca
Carbon, C
Chlorine, Cl
Copper, Cu
Hydrogen, H
Iron, Fe
Magnesium, Mg
Manganese, Mn
Nitrogen, N
Oxygen, O
Phosphorus, P
Potassium, K
Sodium, Na
Sulfur, S
Zinc, Zn
Atomic Weight (g/mole)
40
12
35.5
63.5
1
55.9
24.3
55
14
16
31
39
23
32
65.4
Atomic Weights
Element
Calcium, Ca
Carbon, C
Chlorine, Cl
Copper, Cu
Hydrogen, H
Iron, Fe
Magnesium, Mg
Manganese, Mn
Nitrogen, N
Oxygen, O
Phosphorus, P
Potassium, K
Sodium, Na
Sulfur, S
Zinc, Zn
Atomic Weight (g/mole)
40
12
35.5
63.5
1
55.9
24.3
55
14
16
31
39
23
32
65.4
Ion
Molecular Wt. Valence Equivalent Wt.
(mg/mmole)
(#)
(mg/meq)
Sodium
(Na+)
23
1
23
Calcium
(Ca2+)
40
2
20
Magnesium
(Mg2+)
24
2
12
Sodium: 76 mg/L / 23 mg/meq = 3.3 meq/L
Calcium: 146 mg/L / 20 mg/meq = 7.3 meq/L
Magnesium: 39 mg/L / 12 mg/meq = 3.2 meq/L
SARW = 3.3/ ([7.3 +3.2]/2) 1/2 =
3.3/(5.25) 1/2 = 3.3/2.29 = 1.44
C1-S4
C2-S4
C3-S4
C1-S3
Sodium
Hazard
C4-S4
C2-S3
C1-S2
C3-S3
C2-S2
C4-S3
C3-S2
C1-S1
C2-S1
C4-S2
C3-S1
C4-S1
0.25
1
Class
0.75
2
3
Salinity Hazard
2.25
4
EC(dS/m)
at 25 oC
Problem
With a water-quality report providing a
bicarbonate concentration of 366 mg/L, how do
we express this in meq/L and what is its
significance?
Residual Sodium Carbonate
RSC = [CO3-2] + [HCO3-] - [Ca+2] + [Mg+2]
Where [ ] = ion concentrations in
milliequivalents per liter (meq/L)
Atomic Weights
Element
Calcium, Ca
Carbon, C
Chlorine, Cl
Copper, Cu
Hydrogen, H
Iron, Fe
Magnesium, Mg
Manganese, Mn
Nitrogen, N
Oxygen, O
Phosphorus, P
Potassium, K
Sodium, Na
Sulfur, S
Zinc, Zn
Atomic Weight (g/mole)
40
12
35.5
63.5
1
55.9
24.3
55
14
16
31
39
23
32
65.4
Residual Sodium Carbonate
RSC = [0] + [6.0] - [7.3] - [3.2] = -4.5
RSC Hazard
RSC
HAZARD
<0
none
0-1.25
low
1.25-2.50
medium
>2.50
high
Amendments Required to Neutralize Residual
Carbonates
RSC * 234 lbs gypsum/acre-foot
RSC * 133 lbs sulfuric acid/acre-foot
soil aggregate
H
H
H
O
O
H
+
H
H
Na
O
O
H
H
H
O
O
H
H
H
Na Effects on Soil Permeability
O2 status
hardness
aeration
strength
Soil Porosity
macroporosity
pore continuity
water
 infiltration
 percolation
drainage
retention
Salt-Affected Soils
Soil Types
ESP
SAR
Saline
>4 dS/m < 8.5 <15%
< 12
Sodic
< 4 dS/m >8.5 >15%
>12
Saline-Sodic >4 dS/m >8.5 >15%
>12
SOIL TYPE
ECe
pH
Soil Salinity Hazard
ECe*
HAZARD
< 1.5
low
1.6-3.9
moderate
4.0-5.0
high
>5.0
very high
Soil Sodium Hazard
ESP
SAR
HAZARD
<3
< 2.1
low
3-9%
2.1-7.0
moderate
9-15%
7.1-12.0
high
>15%
>12
very high
Turfgrass Salinity
Tolerance
TOLERANT
(ECe 6.1-10)
MODERATELY
TOLERANT
(ECe 3.1-6.0)
seashore
paspalum (8.6)
alkalaigrass (8.5)
buffalograss (5.3)
fairway
wheatgrass (8.0)
western
wheatgrass (8.0)
St.
Augustinegrass
(6.5)
tall fescue (6.5)
hard fescue (4.5)
blue grama (5.2)
strong creeping
red fescue (4.5)
common
bermudagrass
(4.3)
hybrid
bermudagrass
(3.7)
perennial ryegrass creeping bentgrass
(6.3)
(3.7)
slender creeping
red fescue (6.3)
MODERATELY
SENSITIVE
(ECe 1.6-3.0)
Kentucky
bluegrass (3.0)
zoysiagrass
(2.4)
HIGHLY
SENSITIVE
(ECe <1.5)
centipedegrass
(1.5)
annual
bluegrass (1.5)
colonial
bentgrass (1.5)
rough bentgrass
(1.5)