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Interpretation of Soil and Water Tests for Salt-related
Problems
Glen ObearResearch Technologist
University of Nebraska-Lincoln
PhD Project
Why should we test irrigation water?• Diagnose current problems
• Predict future problems
• Nutrients
Collecting a Water Sample
• Take sample from irrigation head on the golf course
Collecting a Water Sample
• Take sample from irrigation head on the golf course
• Fill container all the way to top
• Seal tightly
• Send to lab the same day you collected
Three Main Problems
1. Salinity
2. Sodicity
3. Toxicity
Three Main Problems
1. Salinity
2. Sodicity
3. Toxicity
Salinity is an available water issue: Water deficit
• Salt concentrations in the soil solution are high enough to limit water uptake
• Soluble salts accumulate on foliage and cause tissue damage
Osmotic Potential: Low Salinity Water
Plant Root
+
+
+
++
+
+
+H20+
+
+
+
Soil Solution
Osmotic Potential: High Salinity Water
Plant Root
+
++
+
++
+
+
+
+
+
+
+
+
+
+
+
+
+
+
H20
Soil Solution
Electrical Conductivity
• ECe (electrical conductivity of soil extract)
• ECw (electrical conductivity of water)
•Units: 1 dS/m = 1 mmhos/cm
Probes can also be used to measure soil or water EC – if measuring in soil it’s important to only measure EC around field capacity
Salinity Hazard of Irrigation Water (ECw)
Salinity Hazard Comments
Westcot and
Ayers
(1985)
EC - dS / m
Low No detrimental effects on plants or soils are
expected.
<0.75
Medium Salt stress may occur on sensitive plants,
preventable with moderate leaching.
0.75 – 1.50
High Salt stress on most plants, leaching and good
drainage necessary.
1.50 – 3.00
Very High Unacceptable for most plants, good drainage,
frequent leaching required.
> 3.00
Salinity Hazard of Irrigation Water (ECw)
Salinity Hazard
Westcot and
Ayers
(1985)
EC - dS / m
Low <0.75
Medium 0.75 – 1.50
High 1.50 – 3.00
Very High > 3.00 ECw: 0.567 dS / m
Salinity Tolerance of Turfgrasses(Soil EC Guidelines; ECe)
Sensitivity Turfgrass Species EC at which
symptoms
may appear
in soil
Sensitive annual bluegrass, colonial
bentgrass, Kentucky
bluegrass, rough bluegrass,
velvet bentgrass
3 dS m-1
Moderately
sensitive
creeping bentgrass, fine fescues 3 – 6 dS m-1
Moderately
tolerant
perennial ryegrass, tall fescue 6 – 10 dS m-1
Key Points: Salinity
• Salinity is an available water issue (i.e., water deficit)
• Water Salinity: ECw
• Soil Salinity: ECe
• Different turf species have different soil EC thresholds
Management of Salinity
• Leaching • Keep salts moving downwards
• Leaching Requirement• How much extra water do we need to apply to remove
salts?
• Frequent irrigation better than deep, infrequent for salinity problems
• Monitor soil salinity periodically
Three Main Problems
1. Salinity
2. Sodicity
3. Toxicity
Sodicity is a soil permeability issue
• When soils have high Na+ content relative to Ca2+
and Mg2+, soil permeability decreases
• Large pores collapse into smaller pores
• Pore continuity decreases
• Drainage and water infiltration rates decrease
• Soil hardness increases
• Soil oxygen decreases, soil moisture increases
Soil is an open fabric
Sodium Swells/Disperses ClayClay no longer “sticky”
Sodium Swells/Disperses ClayClay no longer “sticky”
What about sand-based putting greens?
• Sodium only a potential issue for fine-textured soils containing clay
Evaluating Sodicity in Soil
Sodium Hazard Comments
Exchangeable Sodium
Percentage (ESP)
Low
Soil structure not negatively
affected by sodium < 15
High
Permeability restricted due to high
degree of exchangeable sodium > 15
Varies by soil type (clay content, organic matter content, etc.)
Evaluating Sodicity in Water
• Sodium Adsorption Ratio (SAR):
2
MgCa
NaSAR
Permeability Hazard of Irrigation Water
Sodium
Hazard Comments
Sodium Adsorption
Ratio of Water
(SAR)
Low Can be used to irrigate almost all
soils without structure
deterioration.
< 10
Medium Permeability hazard on fine-textured
soils with high CEC. Best used on
soils with good drainage.
10 - 18
High Structure deterioration and
infiltration reduced on most soils.
Intensive management required.
18 - 26
Very High Generally unacceptable for irrigation. > 26
Permeability Hazard of Irrigation Water
Sodium
Hazard
SAR
Low < 10
Medium 10 - 18
High 18 - 26
Very
High
> 26SAR: 1.6
Adjusted SAR
• Calcium precipitates with carbonate (calcite)
• Sodium increases relative to calcium and magnesium
• Inflates SAR
• Attempts to predict future hazard
2
MgCa
NaSAR
Key Points: Sodicity• Sodicity is a soil permeability issue
• SAR is an irrigation water parameter
• ESP is a soils parameter
• Beware of SARadj
Management of Sodic Soils
• Gypsum (CaSO4)
• Ca2+ replaces Na+ on exchange sites• Higher positive charge = more affinity, stronger attraction
to negatively-charged exchange sites
Three Main Problems
1. Salinity
2. Sodicity
3. Toxicity
Primary Toxic Elements
• Sodium (Na+) and Chloride (Cl-)• Turf much less sensitive than ornamentals
• More concerned about amount in irrigation water rather than soil (contact with foliage)
• Boron (B)• KBG is sensitive at 2-4 mg/kg (ppm) in soil
• Other grasses sensitive to B at 6-10 ppm
• Water levels should be below 1 ppm
Nutrients in Irrigation Water
N added through irrigation
1 ft irrigation´1000 ft2 =1000 ft3waterapplied
1000 ft3irrigation´28.3168L
ft3= 28,316.8Lirrigationapplied
M
Nlb
g
lb
mg
g
L
Nmg
M
irrigationL 6.1
59.453
1
1000
1258.316,28
Simplified Formula
lbsnutrient added
M=mgnutrient
L´0.0624´ ft irrigationapplied
Calcium Interpretation Example
• “Soluble calcium is less than desirable”• Calcium reserves in the soil are inadequate to provide
the desirable amount of soluble Ca2+
Recommendation: Apply foliar calcium
• Liquid calcium chelate• 8.0% calcium
• Apply at 6 oz/M
• Assume 1 gallon weighs 10 lbs
• 128 oz per gallon
How much Ca2+ per 1000 ft2?
Foliar calcium
2
22
2 1000
0375.0
1
08.010
128
1
1000
6
ft
Calb
productlb
Calb
gal
lb
oz
gal
ft
productoz
Irrigation water
• 70 ppm (mg/L) calcium in irrigation water at golf course
How much Ca2+ is applied per M with 0.1 inches of irrigation?
How much Ca2+ from irrigation?lbsnutrient added
M=mgnutrient
L´0.0624´ ft irrigationapplied
M
Calbs
ftL
Camg
2
2
0364.0
0083.00624.070
vs. 0.0375 lbs Ca2+ / M from foliar calcium
0.1inches´1 ft
12inches= 0.0083 ft water applied
• Realistic Scenario: Apply foliar calcium twice a month, apply 2 inches of irrigation per month. How much Ca2+ from foliar calcium, how much Ca2+ from irrigation water?
• Foliar calcium: 0.075 lbs Ca2+ / M
• Irrigation: 0.728 lbs Ca2+ / M
Bicarbonate:Real Problem or Myth?
“Bicarbonates will build up and the soil surface will become sealed restricting air and water movement.”
• Irrigated with water high in bicarbonate for 2.5 years
• No leaching, high ET
• No physical disruption of the soil surface
No negative effects on infiltration
No sealing, crust, or layers formed
Algae
Test irrigation water
• Diagnose current problems, predict future problems• Salinity
• Sodicity
• Toxicity
• Nutrients
• Bicarbonate
Wayne Kussow Graduate Fellowship
Wisconsin Turfgrass Association
Dr. Bill Kreuser
Dr. Doug Soldat
Dr. Chris Williamson
Acknowledgements
