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lead to an increased sodium hazard when usedor irrigation because these residual carbonates

will bind with available calcium and magnesiumin the soil, eliminating some o the eect thoseminerals could have in neutralizing any sodium

surplus. High residual carbonates have the eecto adjusting the eective SAR to even higherlevels than actually measured. RSC is reported

in units o milliequivalents per liter (meq/l).

Table 1. Irrigation Water Suitability.

Water Quality Degree of Problem Factor None Moderate Severe 

EC (µmho/cm) 750 750-3000 >3000

SAR <6 6-9 >9Boron (ppm) <0.75 0.75-2.0 >2.0

Chloride (ppm) <92 92-230 >230RSC (meq/l) <1.25 1.25-2.5 >2.5

Rating Water QualityYour irrigation water test report will have

printed recommendations based on themeasured levels o total salt, sodium, and

boron. There are a number o dierent ways oclassiying the suitability o water or irrigationuse. The suitability is oten the accumulation o

several dierent actors, most importantly totalsalinity, sodicity, boron, chlorides, and residualcarbonates. Moderate hazards in several actors

may be tolerable, while a severe hazard in onearea may be enough to make water unusable or

irrigation.

Nitrate

Nitrate (NO3) in irrigation water is not a quality

problem or plants. It can be a health concern indrinking water, however. To avoid the possibility

o leaching excess nitrates to ground water, it isa good practice to account or any nitrate addedthrough irrigation water when calculating how

much nitrogen ertilizer to apply to achieve youryield goal. Applying 1 inch o irrigation water with

a nitrate content o 1 ppm NO3 as N adds 0.23pounds o nitrogen per acre to your crop.

Related Extension Publications

F-878 Drinking Water TestingL-256 Understanding Your Livestock Water

Test ReportL-296 Understanding Your Household Water

Test Report

MWPS-14 Private Water Systems Handbook.Midwest Plan Service, Ames, IA.

F-2401 Classifcation o Irrigation WaterQuality

Michael A. Kizer

Extension Irrigation Specialist

Hailin Zhang

Director, SWFAL Laboratory

Understanding 

Your Irrigation 

Water Test Report 

Understanding 

Your Irrigation 

Water Test Report 

L-323

Oklahoma Cooperative

Extension Service

Division o Agricultural Sciences

and Natural Resources

Oklahoma State University

Oklahoma State University, in compliance with Title VI and VII o the Civil RightsAct o 1964, Executive Order 11246 as amended, Title IX o the EducationAmendments o 1972, Americans with Disabilities Act o 1990, and other ederallaws and regulations, does not discriminate on the basis o race, color, nationalorigin, gender, age, religion, disability, or status as a veteran in any o its policies,practices or procedures. This includes but is not limited to admissions, employment,fnancial aid, and educational services.

Issued in urtherance o Cooperative Extension work, acts o May 8 and June 30,1914, in cooperation with the U.S. Department o Agriculture, Robert E. Whitson,

Director o Oklahoma Cooperative Extension Service, Oklahoma State University,Stillwater, Oklahoma. This publication is printed and issued by Oklahoma StateUniversity as authorized by the Vice President, Dean, and Director o the Divisiono Agricultural Sciences and Natural Resources and has been prepared anddistributed at a cost o 42 cents per copy.

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The OSU Soil, Water and Forage AnalyticalLaboratory (SWFAL) provides an inexpensive

but comprehensive analysis o water to evaluateits suitability or irrigation o crops and landscapeplants. Water testing is an important frst step in

irrigation development to determine i your watersource contains salts which could damage yoursoil, reduce crop yields, or even kill your plants.

One pint o water is enough or testing. It canbe collected in any clean plastic container. Takethe sample to your county Extension ofce. They

will collect your payment and send your sampleto the laboratory. Results o the test are normallyreturned within one to two weeks.

Your water will be tested or the ollowingactors:

1. Sodium (Na) 10. Bicarbonate (HCO3)

2. Calcium (Ca) 11. Hardness

3. Magnesium (Mg) 12. Alkalinity4. Potassium (K) 13. Total Soluble Salts (TSS)5. Nitrate (NO

3) 14. ElectricalConductivity(EC)

6. Chloride (Cl) 15. pH7. Sulate (SO

4) 16. Percent Sodium (Na%)

8. Boron (B) 17. Residual Carbonate (RSC)

9. Carbonate (CO3) 18. Sodium Adsorption Ratio

(SAR)

The most important actors to consider inirrigation water quality are: (1) total salt content

as measured by electrical conductivity (EC) ortotal soluble salts (TSS); (2) sodium hazard asmeasured by sodium adsorption ratio (SAR) or

sodium percent sodium (Na%); and (3) boron.Pure water is a poor conductor o electricity.

Water with increasing amounts o salt conducts

electric current more and more eectively. TheSWFAL reports electrical conductivity (EC) in units

o micromhos/cm (µmho/cm). Other laboratoriesmay report conductivity in units o millimhos/cm(mmho/cm) or deciSiemens/m (dS/m), which are1000 times larger than µmho/cm.

UNDERSTANDING YOUR IRRIGATION WATER TEST REPORT

TSS and EC

Total soluble salts (TSS) are an indicationo the total salt content o water. It is measured

in units o milligrams per liter (mg/l) or parts permillion (ppm). Both EC and TSS evaluate theoverall eect o salinity and do not indicate the

concentration o individual salts.The eect o total salt content makes it more

difcult or growing plants to take up water rom

the soil. The additional energy the plant must exertto overcome the pull o the salt on the water in thesoil around its roots reduces the perormance o

the plant, leading to stunted growth, lower yieldsand in extreme cases, death o the plant.

The severity o salinity eects vary

widely among plant species. Plants such asBermudagrass and cotton are very tolerant,

being unaected until the electrical conductivityo soil water reaches about 7000 µmho/cm. Incontrast, strawberries and green beans are salt-sensitive, experiencing yield reductions when

the electrical conductivity reaches 1000 µmho/cm.

Sodium

Sodium (Na+) is one mineral that requiresspecial attention in irrigation water. Sodium

can become toxic to many plants at highconcentrations.

Sodium toxicity usually is seen as a burningalong the edges o mature plant leaves. The toxiceects o sodium accumulate over time, so theburning eect in older leaves will eventually move

toward the center o the lea as the lea ages.Woody perennial plants like citrus, deciduousruits and nuts are normally most sensitive to

sodium.Another serious problem o sodium in

irrigation water is its dispersive eect on soil clays.

In soils with signifcant clay content, sodium will

cause the clay particles to separate rom eachother. Dispersion in soil is the reverse process to

aggregation (Ca and Mg promote aggregation).As a result o clay dispersion, soils will have poor

physical properties. This results in a massive

or puddled soil with low water infltration, poortilth and surace soil crust ormation. The claywill clog the soil pores, causing a thin layer o

slowly permeable material near the soil surace.This dramatically reduces the rate at which soilcan absorb water. This sodicity hazard is most

serious in fne-textured soils, especially those withexpanding clays. Sodicity hazard is measuredby SAR or by sodium percentage.

The eect o sodium can be counteracted orreversed by adding calcium to the soil. Calcium,usually in the orm o gypsum, is added to the

soil when the SAR o the topsoil reaches a criticalthreshold level.

Boron

Boron (B) is another mineral o particularimportance in irrigation water. It is an essential

micronutrient to plants, but it can become toxicat very low concentrations. Sensitive plants, suchas nuts, deciduous ruits, and grapes experience

toxic eects when the boron concentration in thesoil reaches 1 ppm. Even the most tolerant plants,such as asparagus and alala are aected once

the soil boron concentration is 4 ppm. Borontoxicity symptoms are similar to those o sodium,with the burning eect beginning at the edges

o older leaves. Woody perennial plants are

generally most sensitive to boron.

Chloride

High concentrations o chloride ions (Cl -)can cause injury to woody perennials, burning

the edges o mature leaves. Other plants canalso be injured by high-chloride water, especiallyi leaves are wet by sprinkler irrigation when the

air temperature is high and humidity is low.

Residual Carbonates

Water with high concentrations o carbonateand bicarbonate relative to the concentrationso calcium and magnesium has a high residual

carbonate level (RSC). This type o water can