interpretation of soil and water tests ... - turfgrass sciencesalinity tolerance of turfgrasses...

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

Glen R. ObearResearch Technologist

University of Nebraska-Lincoln

gobear2@unl.edu

(920) 287-8117