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IRRIGATION WATER ANALYSIS

i

TABLE OF CONTENTS

Acknowledgements ............................................................................................................... ii

I. Irrigation Water Quality Criteria ..................................................................................1

A. Salinity .....................................................................................................................1B. Sodium ....................................................................................................................6C. Cabronate & Bicarbonate .................................................................................... 11D. Phytotoxic Substances ........................................................................................ 12E. Other Phytotoxic Substances ............................................................................. 13F. Sediment .............................................................................................................. 14G. pH .......................................................................................................................... 18H. Nutrient Availability Components ....................................................................... 19

II. Sampling and Handling Guidelines ........................................................................ 20

A. Sample Size ......................................................................................................... 20B. Special Instructions ............................................................................................. 20C. Conversions, Equivalents and Abbreviations .................................................... 21

References Cited.................................................................................................................... 24

Table and Figures Index ........................................................................................................ 25

LIMITATION OF LIABILITY

The information in this publication is based on the best information availableto the author at the time of publication. It is not intended to be used in placeof instructions issued by the manufacturer of any product. All agriculturalmaterials should be used in strict compliance with label directions, and theuser assumes all liability for results of deviation from such directions.

Copyright 1994, Midwest Laboratories, Inc., Omaha, Nebraska

ii

ACKNOWLEDGEMENTS

The following people have lent considerable time and effort into making this publication bothunderstandable and credible. Their efforts and contributions are sincerely appreciated.

Steve Curley; C.P.Ag./S.S.John Menghini; C.P.Ag.Midwest Laboratories, Inc.Editors

Robert Hecht; C.P.Ag.Midwest Laboratories AgronomistSeneca, Kansas

Richard Goff; C.P.Ag.Midwest Laboratories AgronomistNew Ulm, Minnesota

Kennard Pohlman; C.P.Ag./S.S.Managing Director and PresidentMidwest Laboratories, Inc.Omaha, Nebraska

1

INTERPRETATION OFIRRIGATION WATER ANALYSIS

Irrigated crop production largely depends upon management of irrigation water quality. Properinterpretation of the irrigation water analysis is essential in providing management guidelines in theareas of irrigation water suitability, as well as soil and crop management under irrigated conditions.Irrigation water classification guidelines have been developed to allow for proper interpretation of theinterrelationships of the various analytes used in establishing irrigation water quality criteria.

I. IRRIGATION WATER QUALITY CRITERIA

There are four principal hazards related to the chemical nature of a given irrigation water:salinity (sometimes termed total concentration), sodium, bicarbonates, and boron or otherphytotoxic substances (7). A fifth hazard can also be added relating to the physical nature ofwater, that being suspended solids primarily sand, silt and clay sediment (referred to on theirrigation water analysis as total dissolved solids or TDS) (5) (6).

A. Salinity (Total Concentration)

Salinity has been cited as probably the single most important criterion of irrigation waterquality ( 4). Salinity of irrigated soil solution is usually dependent on, and determined by,the salinity of the irrigation water.

The salinity of irrigation water is the sum of all the ionized dissolved salts in the water,hence the expression, total concentration, also is used in labeling salinity (i.e., NO

3-N,

SO4=, Cl-, CO

3=, HCO

3-). Salinity is characterized by electrical conductivity (EC),

because the ability of water to conduct electricity is directly related to the number of ionspresent in the water. Units of EC are most commonly expressed as millimhos percentimeter (mmho/cm), and is the most common and preferred unit of salinity in theUnited States (7).

1. Salinity Effects

The principal effect of salinity is restriction of soil water availability to the plant rootsystem. From a plant physiology standpoint, the presence of salt in soil waterincreases the energy plant roots expend to remove water from the soil. Figure 1depicts the typical relationships between the energy with which a soil holds waterand soil water content for varying salt concentrations in the soil water.

2

Wilting Range

Field Capacity

0 5 10 15 20

0.4% Salt

0.1% Salt

0.2% Salt

Percent Soil Moisture

Wat

er P

oten

tial (

bars

)

15

10

5

0

"0"

fig. 1.

Soil Characteristic Curves for Soil Water with Different Salt Concentrations

Excess salinity can profoundly affect crop physiology and yield by retarding cellenlargement and division, protein and nucleic acid production, and related in-creases in plant mass and physiological processes (5). Visible crop injurysymptoms, such as leaf burn, most likely occur only at extremely high salinity levels(EC >5 mmho/cm), however, yield losses can occur in certain crops at EC valuesas low as 1-3 mmho/cm.

Figure 2 illustrates a typical relationship between crop yield and salinity, where cropyield is shown to be independent of salt concentration as long as salinity is belowa threshold salinity level. Above the threshold salinity level, crop yields decreaseproportionately as salinity increases. The salinity at the zero yield level is anestimate of the maximum salinity a crop can tolerate: crop production is notnormally possible when salinity exceeds the zero yield level for a given crop.

fig. 2. Crop Yield-Salinity Relationship

Threshold Salinity Level100

50

0

Rel

ativ

e C

rop

Yie

ld (

%)

Low High

Salinity

Zero YieldLevel

3

2. Crop Tolerance of Salinity

Crop salinity rating groups as a function of threshold and zero yield salinity level areshown in Table 1 (5).

Table 1.

Threshold and Zero Yield Salinity Levelsfor the Four Salinity Rating Groups

Threshold Salinity1 / Zero Yield Salinity1 /

Salinity Rating Groups (mmho/cm) (mmho/cm)

Sensitive 1.4 8.0Moderately sensitive 3.0 16.0Moderately tolerant 6.0 24.0Tolerant 10.0 32.01/Electrical conductivity of soil saturation extract.

The relationship between crop yield and salinity varies considerably with each crop.Salt tolerant crops, such as barley and cotton have threshold salinity levels thatexceed the zero yield values of salt sensitive crops such as onions and beans.Table 2 summarizes salinity tolerance ratings for selected agricultural crops, andalso depicts salt tolerance thresholds and percent yield decline due to salinity abovethe tolerance threshold level for selected crops.

Table 2.

Salt Tolerance and Percent Yield Decline of Trickle Irrigated Cropsas a Function of the Electrical Conductivity of the Soil Saturation Extract1/

Sensitive Percent Yield Declinea Percent Yield Declinea

%/(mmhos/cm) %/(mmhos/cm)Almond 19 Lemon —Apple — Okra —Apricot 24 Onion 16Avocado — Orange 16Bean 19 Peach 21Blackberry 22 Plum 18Boysenberry 22 Raspberry —Carrot 14 Strawberry 33Grapefruit 16

Moderately Percent Yield Declinea Percent Yield Declinea

Sensitive %/(mmhos/cm) %/(mmhos/cm)Alfalfa — Pepper 14.0Bentgrass — Potato 12.0Broadbean 9.6 Radish 13.0Broccoli 9.2 Rhodegrass —Cabbage 9.7 Rice, paddy —Clover — Sesbania —Corn (forage, grain, sweet) — Sorghum —Cowpea 14.0 Spinach 7.6Cucumber 13.0 Sugarcane 5.9Flax — Sweet potatoes 11.0Grape 9.6 Timothy —Lettuce 13.0 Tomato 9.9Lovegrass — Trefoil, big —Meadow Foxtail — Vetch —Millet, Foxtail —Orchardgrass — a Percent yield decline is the rate of yield reduction per

Peanut 29.0 unit increase in salinity beyond the threshold.

1/Source: G. J. Hoffman, R. S. Ayers, E. J. Doering, and B. L. McNeal, "Salinity in Irrigated Agriculture." In Design and Operation of Farm Irrigation Systems (1981), M. E. Jensen (Ed.),ASAE Monograph 3, p. 145. Copyright ©1980 by ASAE, pp. 158-160. Reprinted by permission of ASAE.

4

Table 2. (cont.)

Salt Tolerance and Percent Yield Decline of Trickle Irrigated Cropsas a Function of the Electrical Conductivity of the Soil Saturation Extract

Moderately Percent Yield Declinea Percent Yield Declinea

Tolerant %/(mmhos/cm) %/(mmhos/cm)

Barley (forage) — Safflower —Beet, garden 9.0 Soybean —Bromegrass — Sudangrass —Canarygrass, reed — Trefoil, Birdsfoot, narrlowleaf —Fescue, tall 5.3 Wheat —Hardinggrass — Wheatgrass, crested andOlive — slender —Ryegrass, perennial — Wildrye, beadless —

Tolerant Percent Yield Declinea Percent Yield Declinea

%/(mmhos/cm) %/(mmhos/cm)

Barley, grain — Sugarbeet —Bermudagrass 6.4 Wheatgrass, fairway and tall —Cotton 7.7 Wildrye, Altai and Russian —Date Palm 3.6

a Percent yield decline is the rate of yield reduction per unit increase in salnity beyond the threshold.

3. Salinity Control

Salinity control measures include leaching salts out of the soil-root profile, maintain-ing high soil-water profile, maintaining high soil-water contents, improving internalsoil drainage and selecting more salt tolerant crops.

a. Leaching Salts

Salts are leached out of the soil-root profile via percolating drainage water.Sufficient water must be applied to leach salts away from the root zone.Tables 3 and 4 show leaching requirements for salinity hazard and leachingrequirement for highest allowable conductivity respectively.

Table 3.

Leaching Requirements for Salinity Hazard1/

Electrical Conductivity Salinity Hazardof the Water Low Medium Highmmhos/cm Leaching Requirement*

1.1 19% 13% 9.5%2.3 40% 27% 20.0%3.5 61% 41% 30.5%

*Assuming 24 inches of irrigation water plus 10 inches of rain per growing season. The percentages listed are the amounts of excess water which will be required to maintain each of the threeclasses of irrigation water.

1/ Determining Water Quality for Irrigation Publication C396, August 1968 Cooperative Extension Service Kansas State University Manhattan, Kansas

5

The leaching requirements needed to maintain low, medium or highsalinity hazards for three classes of irrigation waters are shown in Table3. Leaching requirements for waters which will result in the highestallowable soil conductivity, mmhos/cm, for the low, medium and heavytextured soils respectively are shown in Table 4.

Table 4.

Leaching Requirement for Highest Allowable Conductivity

Salinity HazardLOW MEDIUM HIGH

Soil Water Leaching Water Leaching Water LeachingTexture Conduc- Require- Conduc- Require- Conduc- Require-

tivity ment tivity ment tivity ment

mmhos/cm mmhos/cm mmhos/cmLight 1.40 25% 2.95 35% 4.65 41%Medium 1.10 19% 2.30 27% 3.50 31%Heavy .87 15% 1.87 22% 2.87 25%

Assuming 24 inches of irrigation water plus 10 inches of rain per growing season.

Proper use of Tables 3 and 4 must include certain assumptions:

1). Adequate drainage is present and salt added by soil mineral weatheringand from fertilizers, manures, chemicals, etc., equal the salt removedby precipitation as insoluble minerals and with the harvested crop.

2). The underlying ground water and rainfall salt carried by capillarity intothe root zone are negligible compared to the irrigation water.

3). The initial salinity of the root zone is at or below the desired thresholdvalue (initial leaching to reduce salinity of soils high in natural saltcontents to the desired threshold level may be necessary).

In general, 80 percent of the soluble salts initially present in a soil profile willbe removed by leaching with a depth of water equivalent to the depth of soilto be treated (5). Salt-sensitive crops may have a higher leaching require-ment, while salt-tolerant crops have a lower leaching requirement.

A saturation extract EC (EC determined from solution extracted from asaturated soil paste) can be used to determine the adequacy of the initialleaching application to achieve acceptable salinity threshold levels. Duringsubsequent irrigations, actual salinity levels will exceed the saturation extractEC since the soil will not usually be saturated with water.

b. Maintaining High Soil Water Contents

Lower soil salt concentrations result when the water content of the soil ismaintained at high levels, since salt concentration of the root zone increasesas soil water is depleted by evaporation and plant transpiration. Use of moresaline water is possible by increasing the frequency of irrigation, which

6

maintains high soil water levels. High frequency trickle irrigation has beeneffectively used to apply extremely saline waters; however, caution must beexercised when sprinkler-type irrigation is used with highly saline water assevere leaf burn may result.

c. Drainage

Adequate soil drainage characteristics are essential for soil and crop man-agement utilizing saline irrigation water. Salts from irrigation water, groundwater, natural soil sources, fertilizer, manure, and other chemical sourcesmust be allowed to drain away from the root zone. Naturally high water tableswill complicate drainage of salts and installation of drainage control measuressuch as drainage tile or ditches may have to be added to insure responseunder these conditions. Subsoiling may also be of benefit to the improvmentsof internal drainage. Soil amendments may have to be integrated into thedrainage improvement plan as well; gypsum, elemental sulfur, and sulfuricacid are the most commonly used and cost-effective means via soil applica-tion to help improve soil structure and internal drainage (7). The benefit fromthese amendments can only be realized if the internal drainage can beimproved.

d. Salt-Tolerant Crops

A cultural management tool used under highly saline irrigated conditionswould be to select crops and/or varieties of crops with high tolerances to salt(see Table 2) (6, 7).

B. Sodium

Sodium (Na+) is unique among the cations in its effect on the soil. High concentrationsof sodium in irrigation waters and soils eventually cause deterioration of soil structure(dispersal of soil particles leading to decreasing soil permeability to air and water) andreduction in hydraulic conductivity (decrease in soil water drainage). Additions of evenlow amonts of exchangeable sodium to soils tends to make moist soils impermeable towater and air, and on drying, soil will form dense crusts which interfere with tillage, andseedling germination and emergence.

Indexes developed to form criteria for the tendency of irrrigation water to form exchange-able sodium in the soil include the exchangeable-sodium-percentage (ESP), the sodium-adsorption-ratio (SAR) and the adjusted SAR of soil extracts or irrigation waters.

1. ESP: Equation 1 is used to calculate ESP (5).

Eq. 1. Exchangeable Na+ (meq / 100g soil) ESP = X 100

cation exchange capacity (meq / 100g soil)

Generally, higher ESP levels can be tolerated in coarse-textured than in fine-textured soils.

7

2. SAR

This is the most reliable index of the sodium hazard of irrigation water to formexchangeable sodium in the soil (5), as shown in Equation 2:

Eq. 2.

SAR = Na

+meq / liter( )

Ca2 + meq / liter + Mg 2+ meq / liter( )( )2

Because large amounts of bicarbonate in irrigation water can increase the sodiumhazard in soils, the sodium adsorption ratio (SAR) should include an adjustmentfactor to account for the added effects the precipitation or dissolution of calcium insoils related to carbonate (CO32-) and bicarbonate (HCO3-) concentrations. As thecalcium is precipitated by the high HCO3- and CO32-, it is easily displaced leavingsodium as the dominant cation. The soil stucture can then change causing futherdrainge problems. The adjusted SAR equation is shown in Equation 3:

Eq. 3.

adj. SAR = Na

Ca + Mg

2

1 + 8. 4 − pHc( )[ ]

pHc = (pK’2 - pK’c) + p(Ca + Mg) + pAlkpK’2 is the second dissociation constant for H2SO3 and pHc is the solubility constant for CaCO3 both corrected for ionicstrength.p(Ca + Mg) is the negative logarithm of the molal concentration of calcium plus magnesium.pAlk is the negative logarithm of the molal concentration of the total bases (CO3 + HCO3).pHc is theoretical, calculated pH of irrigation water in contact with lime and in equilibrium with soil CO2.

Obtainedfrom (pK’2 - pK’c) is obtained from using the sum of Ca ÷ Mg + Na in meq/LWater p(Ca + Mg) is obtained from using the sum of Ca + Mg in meq/L

Analysis p(Alk) is obtained from using the sum of CO3 + HCO3 in meq/L

Sum SumConcentration pK’2-pK’c P(Ca + Mg) p(Alk) Concentration pK’2-pK’c p(Ca + Mg) p(Alk)

(meq/L) (meq/L)

.05 2.0 4.6 4.3 2.5 2.2 2.9 2.6

.10 2.0 4.3 4.0 3.0 2.2 2.8 2.5

.15 2.0 4.1 3.8 4.0 2.2 2.7 2.4

.20 2.0 4.0 3.7 5.0 2.2 2.6 2.3

.25 2.0 3.9 3.6 6.0 2.2 2.5 2.2

.30 2.0 3.8 3.5 8.0 2.3 2.4 2.1

.40 2.0 3.7 3.4 10.0 2.3 2.3 2.0

.50 2.1 3.6 3.3 12.5 2.3 2.2 1.9

.75 2.1 3.4 3.1 15.0 2.3 2.1 1.81.00 2.1 3.3 3.0 20.0 2.4 2.0 1.71.25 2.1 3.2 2.9 30.0 2.4 1.8 1.51.5 2.1 3.1 2.8 50.0 2.5 1.6 1.32.0 2.2 3.0 2.7 80.0 2.5 1.4 1.1

Example: Ca = 1.82 meq/L CO3 = 0.05 meq/LMg = 0.75 meq/L HCO3 = 0.3 meq/LNa = 6.70 meq/L

Ca + Mg + Na = 9.27 meq/L From the table: pK’2 - pK’c = 2.3Ca + Mg = 2.57 meq/L p(Ca + Mg) = 2.8

CO3 + HCO3 = 0.35 meq/L p(Alk) = 3.58.6 = pHc

{

8

The relationship between ESP and SAR can be related by a nomogram, as shownin figure 3.

fig. 3

Nomogram for Determing the SAR value of Irrigation Water and for Estimating theCorresponding ESP value of a Soil that is at Equilibrium with the Water

Under field conditions, the actual ESP may be slightly higher than the estimatedequilibrium value, since the total salt concentration of the soil solution is increasedby evaporation and plant transpiration which results in a higher SAR and corre-spondingly higher ESP (7).

Permeability effects are complicated by the interaction of SAR and salinity. Largeconcentrations of dissolved salt tend to neutralize the effect of sodium on soildispersion. Figure 4 illustrates the interaction between EC and SAR and providesa guideline for predicting possible permeability problems (5).

9

Soi

l Per

mea

bilit

y P

robl

em 3

2

1

2010 30

Severe

Increasing

fig. 4

Guidelines for Predicting Possible Permeability Problems

Source: A. Marsh, "Guidelines for Evaluating Water Quality Related to Crop Growth." In: 1982 Technical Conference Proceedings,copyright 1982 by The Irrigation Association, 72 pp. Reprinted by permission of The Irrigation Association.

All water quality combinations of EC and SAR that lie above the curved band shouldhave no permeability problems. Those lying within the curved band have increasingproblems. Those lying below the band will likely develop severe permeabilityproblems even when low SAR waters are utilized.

fig. 5

Diagram for the Classification of Irrigation Waters

ECmmhos/cm

Adj. SAR

SO

DIU

M (

ALK

ALI

) H

AZ

AR

D

None

10

3. Irrigation Water Classification Procedure

The U.S. Salinity Laboratory has developed a procedure for the classification of anirrigation water analysis, relating on a graphic analysis basis, the SAR and thesalinity hazard, as shown in figure 5 (7). The horizontal axis represents salinity asexpressed by conductivity EC (in mmho/c), and the vertical axis represents SAR.To classify an irrigation water analysis, the numerical values for conductivity andSAR are plotted on the diagram figure 5 as coordinates, where the position of thepoint determines the quality classification of the water.

The significance and interpretation of these quality ratings described in figure 5 aresummarized as follows (7):

a. Salinity Classification:

C1 LOW SALINITY WATER can be used for irrigation with most crops onmost soils, with little likelihood that a salinity problem will develop. Someleaching is required, but this occurs under normal irrigation practicesexcept in soils of extremely low permeability.

C2 MEDIUM SALINITY WATER can be used if a moderate amount ofleaching occurs. Plants with moderate salt tolerance can be grown inmost instances without special practices for salinity control.

C3 HIGH SALINITY WATER cannot be used on soil with restricted drain-age. Even with adequate drainage, special management for salinitycontrol may be required, and plants with good salt tolerance should beselected.

C4 VERY HIGH SALINITY WATER is not suitable for irrigation underordinary conditions but may be used occasionally under very specialcircumstances. The soil must be permeable, drainage must beadequate, irrigation water must be applied in excess to provide consid-erable leaching and very salt-tolerant crops should be selected.

b. Sodium Classification:

S1 LOW SODIUM WATER can be used for irrigation on almost all soils,with little danger of the development of a sodium problem. However,sodium-sensitive crops, such as stone-fruit trees and avocados, mayaccumulate injurious amounts of sodium in the leaves.

S2 MEDIUM SODIUM WATER may present a moderate sodium problemin fine-textured (clay) soils unless there is gypsum in the soil. This watercan be used on coarse-textured (sandy) or organic soils that take waterwell.

S3 HIGH SODIUM WATER may produce troublesome sodium problems inmost soils and will require special management—good drainage, highleaching, and additions of organic matter. If there is plenty of

11

gypsum in the soil, a serious problem may not develop for some time.If gypsum is not present, it or some similar material may have to beadded.

S4 VERY HIGH SODIUM WATER is generally unsatisfactory for irrigationexcept at low- or medium-salinity levels where the use of gypsum orsome other amendment makes it possible to use such water.

Summarizing the discussion on classification and interpretation of water analysis,first consideration should be given to the salinity and sodium hazards referring tofigure 5, and the quality-class ratings that follow the diagram. Other independentcharacteristics should then be considered, such as bicarbonate and boron or otherphytotoxic substances, any one of which may change the quality rating of the water.Final use of a water then must also take into account infiltration rate, drainage,quantity of water used, climate, rainfall, and salt tolerance of the crop (7 ). In usingthe guidelines outlined in the classification scheme based off figure 5, averageconditions with respect to one or more of the factors mentioned are assumed. Thisrelationship to average conditions must be accounted for with the use of anygeneral method for the classification of irrigation waters, since unusual circum-stances may alter a recommendation regarding safety of a given water for irrigation.

C. Carbonate and Bicarbonate

Bicarbonate (HCO3-) concentration in irrigation waters is primarily important in itsrelation to calcium (Ca2+) and magnesium (Mg2+). There is a tendency for both calciumand magnesium to react with bicarbonate in the water and/or soil precipitating as eithercalcium carbonate (CaCO3) or magnesium carbonate (MgCO3). Since magnesiumcarbonate is the more soluble, there is less tendency for it to precipitate. The precipitationof either calcium or magnesium from a water as carbonate salts increases the relativeproportion of sodium which directly raises the sodium hazard rating. The potentialbicarbonate hazard rating is shown in Table 5.

Table 5.

Potential Bicarbonate Hazard

Potential Hazard

None to Slight Moderate Severe Very Severe

(ppm HCO3)Bicarbonate 0-120 120-180 180-600 600+

The increase in sodium hazard due to bicarbonate can be determined by calculating theresidual sodium carbonate (RSC) as shown in Equation 4:

Eq. 4

RSC = (CO32- meq/L + HCO3- meq/L) - (Ca2+ meq/L + Mg2+ meq/L)

12

Earlier studies have indicated that waters with RSC values > 2.5 meq/L are probably notsuitable for irrigation purposes; waters containing 1.25 to 2.5 meq/L are marginal; andthose waters containing < 1.25 meq/L RSC are probably safe (7). Marginal waters mightpossibly be made safe with the use of gypsum. RSC values may become less usefulfor waters where concentrations of both calcium and bicarbonate are about equal andhigh (i.e., in the order of 10 meq/L or greater), rendering a very low or zero RSC value.Such waters will precipitate some calcium carbonate and should be considered marginalat best (7).

D. Phytotoxic Substances

While boron (B) is an essential plant micronutrient, certain irrigation waters have beenshown to contain phytotoxic concentrations of boron. Boron toxicity symptoms typicallyappear as yellowing, spotting or drying of leaf tissue at the tip and along the edges of olderleaves. The damage gradually progresses interveinally toward the midleaf. A gumosisor exudate on limbs or trunks is sometimes noticeable on boron toxicity affected treessuch as almond. Many boron sensitive crops show toxicity symptoms when boronconcentrations in leaf blades exceed 250 ppm (4). Not all boron sensitive cropsaccumulate boron in their leaves, such as stone fruits (i.e., peach, plum, and almond),and some pome fruits (i.e., pear, apple, and others), rendering leaf analysis for thesecrops an unreliable boron toxicity indicator (4).

Boron tolerance has been tested for a wide range of crops in sand cultures. Table 6summarizes relative tolerance of selected crops to boron and rates potential toxicity fromboron in irrigation water.

Table 6.

Relative Tolerancea of Crops to Boron

Tolerant Semitolerant Sensitive4.0 mg/L of boron 2.0 mg/L of boron 1.0 mg/L of boron

Asparagus Sunflower, native PecanDate Palm Potato Walnut, black and Persian or EnglishSugarbeet Cotton, Acala and Pima Jersualem artichokeGarden beet Tomato Navy beanAlfalfa Radish PlumBroadbean Field pea PearOnion Olive AppleTurnip Barley GrapeCabbage Wheat Kadota figLettuce Corn PersimmonCarrot Sorghum Cherry

Oat PeachPumpkin ApricotBell pepper Thornless blackberrySweetpotato OrangeLima bean Avocado

GrapefruitLemon

2.0 mg/L of boron 1.0 mg/L of boron 0.3 mg/L of boron

Source: G. J. Hoffman, R. S. Ayers, E. J. Doering and B. L. McNeal, “Salinity in Irrigated Agriculture.” In Design and Operation of Farm Irrigation Systems (1980), M. E.Jensen (Ed.), ASAE Monograph 3, p. 145. Copywrite © 1980 by ASAE, pp. 165. Reprinted by permission of ASAE.aRelative tolerance is based on the boron concentration in irrigation water at which boron toxicity symptoms were observed when plants were grown in sand culture. It does notnecessarily indicate a reduction in crop yield.bTolerance decreses in descending order in each column between the stated limits.

13

Potential Toxicity from Boron

Rating Boron (ppm)

Safe < 0.5Marginal with Increasing Problems 0.5-1.0Problems Can Occur > 1.0

Data in Table 6 are based on the boron level at which toxicity symptoms were observedand do not necessarily indicate corresponding reductions in yield. Studies on many cropnutritional interactions between boron in the soil and plant and potassium, calcium, andsoil and water pH have yet not fully established a sound relationship between boronconcentration and crop yield (4).

E. Other Phytotoxic Substances

Very few substances other than boron occur in toxic concentrations in natural waters( 7). Excess chloride concentrations in soil solution have been shown to be phytotoxicfor certain crops (some citrus, stone fruit, avocado, grape, olive, some berries andstrawberries) (6). Table 7 shows irrigation water ratings for potential toxicity fromchloride.

Table 7.

Potential Toxicity from Chloride

Rating Chloride (ppm)

Safe 0-70Marginal with Increasing Problems 70-300Problems Can Occur > 300

Other phytotoxic substances contained in irrigation water may be from those watersobtained from industrial waste effluent that have been discharged into surface streams.Irrigation water analysis is a critical management component of crop and soil manage-ment when irrigating from surface water sources. Table 8 shows guidelines for fieldapplication of pulpmill effluents (7).

Table 8.

Guides for Field Application of Pulpmill Effluents

BOD < 200 lb/acre dayColor Individual site investigationpH 6.5-9.0SAR < 8 on permeable soils

The possible effects or residues from pesticides that are normally encountered inirrigation waters cannot entirely be ignored, however minute the pesticide quantity maybe. The greatest concern would come from irrigating with tailwaters or reuse pits,streams and/or runoff control stuctures. No firm evidence has been established whetheror not significant amounts of pesticides and herbicides enter waterways used for

14

irrigation or leave by way of irrigation return flow (7). Some chlorinated pesticides areknown to persist for long periods in the soil, but is conjectural to assume they are washedfrom the soil to reappear in water courses. Some evidence has been found that

where water channels are sprayed for weed control with herbicides such as 2,4-D and2,4-5-T, residues (in parts per trillion) were more likely to be persistently found in irrigationreturn flow (7).

F. Sediment

Sediment hazards contained in irrigation water are primarily a concern limited to trickleirrigation systems. However, if the irrigation water source is from natural stream waters,or holding ponds, any irrigation system may be subject to clogging of intake screens andpumps. Table 9 shows classification of screens and particle sizes in micrometers (µm),with figure 6 showing the relationship of different particle sizes (6).

Table 9.

Classification of Screens and Particle Sizes

Screen Equivalent Particle EquivalentMesh No. Diameter Designation Diameter

(micrometer) (micrometer)

16 1180 Coarse sand > 100020 850 Medium sand 250-50030 600 Very fine sand 50-25040 425 Silt 2-50

100 150 Clay < 2140 106 Bacteria 0.4-2170 90 Virus < 0.4200 75270 53400 38

fig. 6

Relationship of Different Particle Sizes

50 µm

150 µm

20 µm2 µm

15

A total dissolved solids (TDS) in units of ppm is determined to assess sediment contenteffect on any given irrigation water quality analysis.

Filtration may be required for optimum irrigation system performance and is usuallyalways required for optimum trickle irrigation system performance. Settling basins, sandor media filters, screens, cartridge filter and centrifugal separators are the primarydevices used to remove suspended material in irrigation water (5). Tables 10, 11, 12, and13, along with figure 7, summarize filter effectiveness, requirements, and variousschematic descriptions of sediment removing devices.

Table 10.

Physical, Chemical and Biological Contributors to Clogging of Trickle Systems

A. Physical B. Chemical C. Biological(Suspended Particles) (Precipitation) (Bacteria and Algae)

a. Organic a. Calcium carbonate a. Filaments(1) Moss, aquatic b. Calciumsulfate b. Slime

plants, and algae c. Heavy metal, hydroxides, c. Microbial deposition(2) fish, snails, etc. oxides, carbonates (1) Iron

b. Inorganic silicates, and sulfides (2) Sulfur(1) Sand d. Fertilizers (3) Manganese(2) Silt (1) Phosphate(3) Clay (2) Aqueous ammonia

(3) Iron, zinc, copper, manganese

Source: D. A. Bucks, F. S. Nakayama, and R. G. Gilbert, "Trickle Irrigation Water Quality and PreventiveMaintenance."Agricultural Water Managment copyright ©1979 by Elsevier Science Publishing Co., Inc. p. 151. Reprintedby permission of Elsevier Science Publishing Co., Inc. and authors.

Table 11.

Control of Trickle System Clogging Filter Effectiveness

Filter Type Size Range (microns)

Sediment basins > 40Slotted cartridge > 152Sand media 5 - 100Sand media > 20Screen (100-200 mesh) 75-150Screen (200 mesh) > 100Screen > 75Separatora > 74Separatora (two stage) > 44

Source: W. M. Shannon, "Sedimentation in Trickle Irrigation Laterals," unpublished M. S. Thesis (1980),Washington State University, Pullman, 133 pp.aSeparators remove 98 percent of particles larger than size indicated.

16

Table 12.

Filtration Capabilities of Different Screen Mesh Sizes

Mesh Filtration to Micron Size

80 175100 147150 104200 74

Note: For example, a 100-mesh screen will filter everything larger than 147 microns in size out of the irrigationwater.

Table 13.

Filtration Requirements for Selected Physical Clogging Agents

Water Quality Suggested Treatment

Inorganic Solids< 10 mg/L

Particles greater than 100 Remove with stainless-steel screen.microns in diameter (Particles larger than one-sixth of emitter

orifice diameter should be screened out)

Particles less than 100 microns in These particles may pass through the irrigationdiameter system if the Fe and S concentrations are not

too high. If slug loadings are frequent, thenautomatic screen cleaning may be required.

< 10 mg/LParticles over or under Automatic cleaning of screens suggested.100 microns

Organic Solids< 10 mg/L

Particles over 100 microns Sand filters are required. Recommendedflowrate through sand filter is 20 gpm/ft2. of bedarea. Manual backflushing should besatisfactory.

< 10 mg/LParticles over 100 microns Sand filters with automatic backflush are

required. Recommended flowrate through sandfilter is 20 gpm/ft.2 of bed area.

Slug loadings of organic solids with High suspended solids loadings of this typeparticles under 100 microns of materal may not pass through the trickle

irrigation system. In this situation, sandfilters will remove a larger volume of material.Automatic backflushing of the sand filters willmost likely be required.

Treatment with chlorine may be requiredperiodically during the season to preventaccumulation of particles under 100 microns.

17

fig. 7

Schematic Description of Various Sediment Removing Devices

Typical (a) "Y" and (b) basket filters used for secondary filtration in trickle irrigaion systems. They arenormally installed at the upstream end of submains and laterals.

18

1/The Tennessee Valley Authority (TVA) has conducted studies showing that formation of insoluble calcium and magnesiumpyrophosphates upon additions of APP into hard irrigation water could be avoided by adding phosphoric acid to decrease the pH of theAPP base solution to 4 or lower (1).

fig. 7 (continued)

Sand Medial Filter. (a) Filtering process. Screen Filter. (a) Filtration Progress.(b) Backwash process. (b) Throughflush process.

G. pH

pH is a measurement for acidity or alkalinity. A pH of 7.0 is considered neutral, while apH reading below 7.0 is considered acidic, and a reading above 7.0 is considered alkaline.Most well waters tend to be in the alkaline range, with pH’s in the 7.0 to 8.3 range, whilesome stream waters may be slightly acid (pH 6.5). With alkaline waters being utilized forirrigation, care may have to be taken if certain fertilizer and/or herbicides and pesticidesare to be injected into the water (fertigation/chemigation).

Fertigation of ammonium polyphosphate (APP) and certain micronutrients (notably zinc,manganese and iron) into an alkaline water will generally cause those fertilizer nutrientsto precipitate out as insoluble compounds and rendered plant unavailable. APP solutionsmay react in hard water (high calcium, magnesium and bicarbonate content) forming aprecipitant (calcium ammonium pyrophosphate) ( 2) which collects on the walls of thepipes and nozzles and eventually causes plugging. A simple test for APP compatibilitywith the irrigation water follows (3):

1. Measure amount of irrigation water in milliliters (mL.) equal to the gpm pumpingrate, i.e., 950 gpm = 950 mL.

2. Add the number of mL. of APP equal to the desired APP pumping rate to themeasured amount of irrigation water.

3. If a cloudy precipitate forms, the addition of APP to this irrigation water is notadvisable.1/

Urea-phosphate solutions (UP) are acid-based phosphate fertilizer formulations thathave shown promise for use in irrigation systems with hard water. These formulations

19

will sequester calcium and magnesium preventing formation of precipitate in the irrigationwater ( 1). Base solutions made from UP and water resulting in an 8-20-0 grade havea pH of 1.5, made by dissolving crystalline UP in water with added heat (125½ F:dissolution time of five minutes; heat of 150½ F allows dissolution in one minute). Studiesconducted by TVA with two relatively hard irrigation waters (the Republican River nearCulbertson, Nebraska, and the Colorado River in Colorado) using a UP 8-20-0 solutionshowed no precipitation difficulties (1). Resulting pH of the applied irrigation water was7.0 and 6.8, respectively. For practical use in irrigation systems, about 800 gallons ofwater per pound of P2O5 per acre should be applied. This rate of application in hard wateris possible using UP 8-20-0 base solution, while in the same waters only 25 gallons ofwater per pound of P2O5 can be applied without precipitation problems using APP 10-34-0 (1).

H. Nutrient Availability Components

Essential plant nutrients included in Midwest Laboratories’ irrigation water report includecalcium (Ca2+), magnesium (Mg2+), nitrate nitrogen (NO3--N), sulfate (SO4=), phospho-rus (P), potassium (K+), chloride (Cl-), and boron (B). All nutrient concentrations areexpressed as ppm. Following is a brief discussion of the plant-essential nutrientscontained in the irrigation water analysis:

1. Nitrate-Nitrogen (NO3--N)

NO3--N is commonly found in irrigation water sources either from soil applicationof ammoniacal nitrogen fertilizers or conversion of soil organic matter nitrogen vianitrification to NO3--N. Determination of NO3--N content in irrigation water plays animportant role in irrigated crop nitrogen management strategies. To determineavailable nitrate-N per acre inch of waer applied, multiply ppm NO3-N by 0.23.

2. Phosphorus (P) and Potassium (K)

Determination for these elements is made primarily for crop nutrient managementstrategies.

3. Chloride (Cl-) and Boron (B)

While both of these nutrients are plant-essential, their content in irrigation water ismore of a concern when evaluating water quality criteria; Cl- and B are discussedin that light in the water quality section, pp. 12 to 13.

Table 14.

Nutrient Availability in Irrigation Water (ppm)

Rating Ca Mg K P N NO3 SO4 S

Low < 20 < 10 < 5 < 0.1 < 1 < 5 < 30 < 10Normal 20-60 10-25 5-20 0.1-0.4 1-10 5-50 30-90 10-30High 60-80 25-35 20-30 0.5-0.8 10-20 50-100 90-180 30-60Very High > 80 > 35 > 30 > 0.8 > 20 > 100 > 180 > 60

20

Table 15.

Trace Element Tolerances for Irrigation Water

For Water Used For Short-Term UseContinuously on on Fine-Textured

Element All Soils Soils Onlyppm ppm

Aluminum (Al) 1.0 20.0Arsenic (As) 1.0 10.0Beryllium (Be) 0.5 1.0Boron (B) 0.75 2.0Cadmium (Cd) 0.005 0.05Chromium (Cr) (hexavalent) 5.0 20.0Cobalt (Co) 0.2 10.0Copper (Cu) 0.2 5.0Fluorine (Fl) (*) (*)Iron (Fe) (*) (*)Lead (Pb) 5.0 20.0Lithium (Li) 5.0 5.0Manganese (Mn) 2.0 20.0Molybdenum (Mo) 0.005 0.05Nickel (Ni) 0.5 2.0Selenium (Se) 0.05 0.05Tin (Sn) (*) (*)Tungsten (W) (*) (*)Vanadium (V) 10.0 10.0Zinc (Zn) 5.0 10.0

*No established level.

II. SAMPLING AND HANDLING GUIDELINES

Proper sampling is a must in obtaining a representative water sample.

Irrigation water samples should not be collected until after the well has pumped for a period ofone or two hours or until the water has cleared.

Stream, pond and catch pit water samples should be taken during the period of tme when theyare being used for irrgation or a water source for livestock. It may be necessary to collectseveral samples during the season to correlate to evaporation and dilution.

A. Sample Size

An 8-16 ounce sample of water is sufficient for most quality and nutrient analysis. Rinsethe contaienr several times with the water being sampled before collecting the finalsample. Remember to rinse the lid also. Make certain that the bottle cap is tightly sealedbefore packaging shipment.

B. Special Instructions

1. Clean plastic containers can be used for most regular analysis. However, forsamples which are to checked for the presence of organic residues, such as

21

insecticides or herbicides, a glass container must be used.2. Accurate iron tests can be made only if the sample has been made acid

immediately after collection. This will require a separate sample. Ask the laboratoryfor special instructions.

3. Mail the sample(s) to the laboratory as soon as possible after collection.

C. Conversions, Equivalents, and Abbreviations

1. Common Conversions

To convert P to P2O5, multiply by 2.29To convert K to K2O, multiply by 1.23To convert Mg to MgO, multiply by 1.658To convert Ca to CaCO3, multiply by 2.50To convert SO4 to S, multiply by 0.333To convert NO3 to N, multiply by 0.226

2. Equivalent Weight of Ions

Equivalent EquivalentCations Weight Anions Weight

Calcium (Ca) 20 Carbonate (CO3) 30Magnesium (Mg) 12 Biocarbonate (HCO3) 61Sodium (Na) 23 Sulfate (SO4) 38

Chloride (Cl) 35.5

3. Symbols--Abbreviations--Conversions

EC .................................................. Electrical Conductivity in mhos/cmEC X 10-3 ...................................... Electrical Conductivity in millimhos/cmEC X 10-6 ...................................... Electrical Conductivity in micromhos/cmSAR ............................................... Sodium Absorption Ratiomeq ............................................... Milliequivalentmeq/L ............................................ Milliequivalent/Lppm ............................................... Parts per millionL ..................................................... Liter

grains per gallon to parts per million ppm = 17.1 x grains per gallonone U.S. gallon weighs 8.345 poundsone cubic foot of water weights 62.43 pounds< less than> greater than450 gallons per minute (gpm) = 1 acre-inch per hour1 cubit foot per second (cfs) = 1 acre-inch per hourpounds of water = 226,500 x acre-inchesone acre foot of water weights 1,360 tonsppm x 0.23 = lbs./acre inch

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REFERENCES

1. Achorn, F. P. 1984. Acid fertilizers. In Proceedings: Great Plains Fertility Workshop. Denver,Colo. 12 p.

2. Duis, J. H. 1969. Polyphosphates in Irrigation. Solutions Magazine. March-April, 1969.

3. Hergert, G. W. 1976. Sprinkler application of fertilizer nutrients. Solutions Magazine. 1976.

4. Hoffman, G. J. Management Principles: Salinity. P. 345-362. In: F. S. Nakayama and D. A.Bucks (ed.) Developments in Agricultural Engineering 9: Trickle Irrigation for Crop Production;Design, Operation and Management. 1986. Elsevier.

5. James, L. G. Water for Irrigation. P. 110-148. In: L. G. James (ed.) Principles of Farm IrrigationSystem Design. 1988. John Wiley and Sons, Inc.

6. Nakayama, F. S., Operational Principles: Water Treatment. P. 164-187. In: F. S. Nakayama andD. A. Bucks (ed.) Developments in Agricultural Engineering 9: Trickle Irrigation for Crop Production;Design, Operation and Management. 1986. Elsevier.

7. Wilcox, L. V. and W. H. Duram. Quality of Irrigation Water. P. 104-122. In: R. M. Hagan, H. R.Harse. T. W. Edminster (ed.) Irrigation of Agricultural Lands. Agronomy Monograph No. 11.American Society of Agronomy. Madison, Wisconsin.

25

TABLES AND FIGURES INDEX

Bicarbonate, potential hazard (Table 5) .............................................................................................. 11Boron

tolerance (Table 6)................................................................................................................. 12toxicity ................................................................................................................................... 13

Chloride, toxicity (Table 7) .................................................................................................................. 13Clogging, physical, chemical and biological contributors (Table 10) .................................................... 15Crop-yield salinity relationship (fig. 2)............................................................................................. 2Filters

clogging effectiveness (Table 11) ..................................................................................... 15various designs (fig. 7) .................................................................................................17-18

Filtrationcapabilities (Table 12) ....................................................................................................... 16requirements (Table 13) .................................................................................................... 16

Irrigation waterclassification (fig. 5) ............................................................................................................. 9nomogram for SAR and ESP relationship (fig. 3) ............................................................. 8

Leaching requirementfor highest allowable conductivity (Table 4) ...................................................................... 5for salinity hazard (Table 3) ................................................................................................ 4

Nutrient availability in irrigation water (Table 14)......................................................................... 19Particle size relationship (fig. 6) .................................................................................................... 14Permeabiliy problems guidelines (fig. 4) ........................................................................................ 9Pulpmill effluents, guides for field application (Table 8) .............................................................. 13Salinity levels, threshold and zero yield (Table 1) ......................................................................... 3Salt tolerance, percent yield decline of irrigated crops (Table 2) ................................................. 3Screens, classifications and sediment particle sizes (Table 9) .................................................. 14Soil characteristic curves, soil water and salt concentrations (fig. 1) .......................................... 2Trace element tolerances for irrigation water (Table 15) ............................................................ 20