L 323 Irrigation
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Transcript of L 323 Irrigation
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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