siw-1 soil and irrigation water manual -...

©Hach Company, 1992. All rights reserved. Printed in the U.S.A.rb 1/01

24960-88

SIW-1 SOIL AND IRRIGATION WATER MANUAL

ii

TABLE OF CONTENTS

Page

PREFACEReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

SECTION 1 INTRODUCTIONUsing This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Extracting Soil Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Extraction Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Using The Apparatus in the Kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Reading the Meniscus in Droppers and Cylinders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Using The Color Comparator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Using the Soil Scoops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

SECTION 2 SAMPLE COLLECTION AND PREPARATIONSampling, Drying, Grinding and Screening Soil Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Filtering Soil Extracts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Obtaining Water Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

SECTION 3 SOIL EXTRACTION PROCEDURESAqueous Extraction (for salinity and pH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Calcium Sulfate Extraction (for nitrate-nitrogen) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Mehlich 2 Extraction (for calcium + magnesium, phosphorus, potassium) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10Potassium Chloride Extraction (for total exchangeable acidity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Saturated Calcium Sulfate Extraction (for gypsum requirement and exchangeable sodium) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14SMP Buffer Extraction (for lime requirement) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

SECTION 4 SOIL ANALYSIS PROCEDURESCation Exchange and Percent Base Saturation Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Gypsum Requirement—EDTA titration method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Calcium + Magnesium—EDTA titration method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Free Lime Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Lime Requirement—Electrode method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25Nitrate-Nitrogen—Cadmium Reduction method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29pH—Electrode method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Phosphorus—Ascorbic Acid method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Potassium, Exchangeable—Turbidimetric Tetraphenylborate method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37Salinity (Conductivity)—Electrode method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Texture Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41Total Exchangeable Acidity—NaOH titration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

SECTION 5 IRRIGATION WATER ANALYSIS PROCEDURESConductivity—Electrode method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Calcium + Magnesium—EDTA titration method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47Nitrate-Nitrogen—Cadmium Reduction method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49pH—Electrode method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51Phosphorus—Ascorbic Acid method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53Sodium Estimation and Sodium Adsorption Ratio Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

ORDERING AND TECHNICAL ASSISTANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

iii

SIW-1 SOIL TEST KIT MANUAL

PREFACEThis test kit provides basic analyses for soil fertility assessmentand irrigation water quality when routine laboratory analysis isnot convenient or economical. This includes remote areaswhere facilities are not available or in a classroom where aninstructor wants to present the basics of soil analysis withoutusing expensive or sophisticated equipment. Prepackagedchemicals, simplified equipment and easy-to-follow proceduresmake Hach methods easy and quick to use.

The test kit was designed to meet the needs of professionalscientists and non-scientists alike. Every possible effort wasmade to insure the results will be meaningful and applicable.The data obtained should lead the analyst to interpretations thatcorrelate with interpretations from a competent full service soillaboratory. When possible, Hach Company used proven andaccepted methodology in this kit. The procedures in thismanual were modified from the following books andpublications.

1. Handbook on Reference Methods For Soil Testing, Revised Edition—1980The Council On Soil Testing and Plant Analysis1111 Plant Science BuildingUniversity of GeorgiaAthens, Georgia

2. Recommended Chemical Soil Test Procedures for the North Central RegionBulletin No. 499 (Revised)North Central Regional Publication No. 221 (Revised)North Dakota Agricultural Experiment StationNorth Dakota State UniversityFargo, North Dakota 58105

3. Diagnosis and Improvement of Saline and Alkali SoilsAgricultural Handbook No. 60United States Department of AgricultureIssued February 1954 (Out of Print)Compiled by the United States Salinity Laboratory Staff

4. Methods of Soil Analysis, Part 2American Society of AgronomyMadison, Wisconsin1965

5. Soil Testing and Plant Analysis, Third EditionSoil Science Society of America, Inc.1991

1

SECTION 1 INTRODUCTION

SOIL AND IRRIGATION WATER MANUALSThe two manuals supplied with this kit acquaint users withHach procedures and techniques necessary for soil andirrigation water characterization. The Soil and Irrigation WaterManual—SIW-1 contains directions for performing theanalyses. This manual has been printed on special waterproof,tear-resistant paper.

The Hach Soil and Irrigation Water Interpretation Manualhelps interpret the results by providing basic information on soilfertility, soil characterization, plant nutrition, fertilizerrecommendation, and irrigation water quality. This manual alsocontains a section on common conversion factors used in soiland water analysis, a glossary of terms, reorder information,and technical support information. The final pages of themanual contain data recording sheets to help the analyst recorddata and calculations form the analyses.

USING THIS MANUALThis manual is arranged in sequential sections. The first sectionacquaints the reader with some of the equipment and analyticaltechniques used with the apparatus. The second section coverssampling and sample preparation for analysis. Soil Extractionsare covered in the next section (see information below) andSection 4 contains the soil analysis procedures in alphabeticalorder. The last section contains the water analysis procedures.

EXTRACTING SOIL SAMPLESTo analyze for a specific substance(s) in a soil, you often needto extract that substance from the soil with a solvent(extractant). The analysis is then completed on the solutioncontaining the substance.

This manual contains six extraction procedures. Thefollowing Extraction Guide outlines which extractions areused when analyzing for the specific substances orparameters listed below each extraction. It is important touse the indicated extraction. More than one type ofextraction may be necessary for a given sample.

EXTRACTION GUIDE

Aqueous Extraction Calcium Sulfate Extraction↓ ↓

pH Nitrate-NitrogenSalinity

Mehlich 2 Extraction Potassium Chloride Extraction↓ ↓

Phosphorus Total Exchangeable AcidityPotassiumCalcium

Magnesium

Saturated Calcium SMP Buffer ExtractionSulfate Extraction ↓

↓ Lime RequirementGypsum RequirementExchangeable Sodium

The Mehlich 2 Soil Extract was chosen for several reasons:

1. Mehlich 2 is a viable choice for phosphorus extraction frommost types of soils.

2. This reagent will extract as much or more phosphorus frommost soils than other common extracts, resulting in more colordevelopment and therefore more accurate visual comparison ofthe color.

3. Other macronutrients (i.e., potassium, calcium, andmagnesium) are extracted with Mehlich 2, allowing for theirmeasurement and subsequent determination of cation exchangecapacity and percent base saturation.

Two methods for determining lime requirement are included inthis manual. The SMP buffer method is used for soils that havea lime requirement above 2 tons/acre. For soils that have a limerequirement below 2 tons/acre or in tropicals soils with highreserves of aluminum, the determination of total exchangeableacidity should be considered.

For convenience, soil salinity is determined with this kit using a1:1 soil suspension instead of a saturated paste extract.However, where salinity management and leachingrequirements are of prime importance, salinity should bedetermined using the traditional saturated paste method. HachCompany provides a Soil Saturation Extract Kit (Cat. No.18700-00) to use with the Pocket Pal TDS Tester.

2

USING THE APPARATUS IN THE KITAccurately Measuring Liquids Using Eye Droppers andGraduated Cylinders

When small sample quantities are used, the accuracy ofmeasurements is important. Figure 1 below illustrates theproper technique for reading the sample level or the meniscusformed when the liquid wets the cylinder or wall of the dropper.

FIGURE 1 READING THE MENISCUS

FIGURE 2 COLOR COMPARATOR

FIGURE 3

USING THE COLOR COMPARATORThe figures below illustrate how to use the Color Comparator toread the color viewing tubes. After color development:

1. Insert the blank (untreated sample) and sample (preparedsample) tubes in the correct openings (Figure 2).

2. Hold the Comparator so a light source is behind theComparator as you look through the color matching windows(Figure 3).

3. Rotate the color disc until the color in the untreated samplewindow matches the color in the prepared sample window(Figure 4).

4. Read the concentration from the scale window.

Note: The standards in the kit may be used to practice the technique for readingsamples using the comparator.

FIGURE 4

35

45

50

40

SCALEWINDOW

PREPAREDSAMPLE

VIEWING TUBES

SCALE WINDOW

UNTREATEDSAMPLE

COLORMATCHINGWINDOWS

COLORMATCHINGWINDOWS

3

USING THE SOIL SCOOPSA set of soil scoops is included with the kit for samplemeasurement. The set consists of three different sized scoops:0.85 cc (1 g), 1.70 cc (2 g), and 4.25 cc (5 g). In addition, a0.1 g spoon is included for use in the procedures.

Use the following procedure when using the scoops1. Use a spatula to stir the soil sample.

2. Dip the scoop into the center of the soil sample to obtain aheaping scoop full.

3. Hold the scoop firmly and tap the handle of the scoop sharplythree times with a spatula to settle the soil.

4. Hold the blade of the spatula perpendicular to the top of thescoop and strike off the excess soil.

5. Empty the soil into the appropriate container for a givenprocedure.

4

SECTION 2 SAMPLE COLLECTION AND PREPARATION

SOIL PREPARATION

SAMPLING, DRYING, GRINDING ANDSCREENINGThe following method is commonly used to prepare soilsamples for subsequent testing. It applies to all classes of soils.The procedure is based on the Recommended Chemical SoilTest Procedures for the North Central Region, Bulletin No.499 (Revised), October, 1980 published by The North DakotaAgricultural Experiment Station, North Dakota StateUniversity.

SOIL SAMPLINGFor meaningful results, it is of utmost importance that the soilsample be representative of the area being tested.

Depending on the size of the sampling area, take 15 to 20subsamples from the area being sampled and mix them togetherin a clean container. Use a sample of this mixture duringanalysis to represent the area being tested. Subsamples (whichshould be approximately the same size) may be obtained with acoring tube, soil auger or shovel. Avoid sampling very unusualareas such as old manure piles, lime piles, fence lines, etc.REMEMBER THE TEST RESULTS CAN NO BETTERREPRESENT THE TESTING AREA THAN DOES THESOIL SAMPLE FROM THAT AREA. The most validinformation regarding sampling can be obtained from the localextension office.

Sample preparation consists of drying, crushing, mixing andsieving. These steps assure that a correct, representativesample is analyzed. Dry the sample as outlined below.

1. Break up the large chunksof soil and spread it out to airdry. Avoid contamination byfertilizer dusts or other suchsources of contamination. If aforced-draft oven or similardrying device is used, set theheat no higher than60 °C (140 °F).

2. Use a short 2x4 board orsimilar device to crush the airdried soil.

3. Pass the crushed soilthrough the 10-mesh (2 mm)soil sieve assembly includedwith the kit.

4. Store the soil in a cool, dryplace until the analysis iscomplete.

DRYING PROCEDURE

5. It is always wise to savesamples being analyzed incase re-testing is necessary.

Þ

Store inCool, Dry

Place

Keep SampleFor RepeatAnalysis

5

FILTERING SOIL EXTRACTSPrepare a filter for filtration as follows:1. Fold a piece of filter paper as illustrated in Figure 5.

2. Open the filter in a manner that forms an inverted cone.Check the filter paper for holes or tears—they can make theresults inaccurate.

3. Rinse the funnel with deionized water. Shake the funnel toremove excess water.

4. Place the filter paper in the funnel.

5. Place the funnel into a round sample bottle or plastic cup tocollect the extract.

FIGURE 5 FOLDING THE FILTER PAPERFold a sheet of filter paper by creasing it in half and then in halfagain. Separate one edge from the other three to form a cone.Place the folded paper in the funnel.

OBTAINING WATER SAMPLESThe minimum volume of water recommended for analysis isapproximately 1 liter. Take care to obtain a representativesample. Satisfactory samples of some waters can be obtainedonly by mixing several portions collected at different times.Collection and mixing technique depend on local conditions:

• Samples from wells should be collected after the pump hasrun for 10 minutes

• Samples from streams should be taken from running water

In general, the shorter the elapsed time between collection andanalysis of a sample, the more reliable the analytical data willbe. Changes resulting from chemical and biological activitymay alter the composition of the sample.

Use the following procedure to obtain a water sample:1. Rinse the sample container 3 times with the water to beanalyzed.

2. Fill the container completely full with the water to beanalyzed and cap tightly.

3. Analyze the sample as soon as possible.

6

SECTION 3 SOIL EXTRACTION PROCEDURES

1. Using a 5-gram scoop,measure 4 scoops of theprepared soil sample into a 50mL plastic beaker.

2. Using a 25-mL graduatedcylinder, accurately measure20 mL of deionized water andtransfer it to the 50-mLbeaker.

3. Repeat steps 1 - 2 for eachsoil sample undergoingextraction.

Note: To prevent confusion whenworking with several samples, labeleach beaker with the sample or testname.

4. Using the spatula, stir thecontents of the beaker for 1minute at 10-minute intervalsover a 30 minute period.Note: Rinse the spatula withdeionized water before stirring eachsample.

Aqueous Extraction Method for SoilUsed for: Salinity and pH

Use the Aqueous Extraction method to prepare the soil samplefor salinity and pH measurements. The soil suspension doesnot need to be filtered to determine pH and salinity—measurements can be made directly in the suspension.

Before extraction, dry the soil sample, then screen it to afineness of 0-2 mm using the Hach Soil Sieve in the kit.Careful preparation is important to assure volumetricmeasurement of the soil sample. Refer to the introductorysections for soil sampling and sample preparation.

AQUEOUS EXTRACTION PROCEDURE

5. After 30 minutes, use theprepared sample for salinityand pH determination. Note: Because conductivity isaffected by minute amounts ofpotassium chloride resulting from pHdetermination, measure the salinityof the sample before measuring pH.

Repeat foreach sample

30 minutes

7

AQUEOUS EXTRACTION, continued

APPARATUSCat. No.

Beaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41Cylinder, Graduated, Polymethylpentene, 25 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Soil Scoop, 5 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-05Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00Spatula, Stainless Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561-62

8

Calcium Sulfate Extraction For SoilUsed for: Nitrate-Nitrogen

The Calcium Sulfate Extraction is used to extract nitrate-nitrogen from soils and can be used for all classes of soils.

Before extraction, dry the soil sample, then screen to a finenessof 0-2 mm using the Hach Soil Sieve in the kit. Carefulpreparation is important to assure volumetric measurement ofthe soil sample. Refer to the introductory sections for soilsampling and sample preparation.

CALCIUM SULFATE EXTRACTION PROCEDURE

1. Using a 5-gram soil scoop,measure 2 scoops of theprepared soil sample into around sample bottle.

2. Using the 0.1-gram plasticspoon, add 1 level spoonful ofCalcium Sulfate to the roundsample bottle containing thesample.

3. Using a 25-mL graduatedcylinder, accurately measure20 mL of deionized water intothe cylinder and transfer it tothe round mixing bottle.

4. Repeat steps 1–3 for eachsoil sample undergoingextraction.

Note: To prevent confusion whenworking with several samples, labeleach sample bottle with the sample ortest name.

5. Cap and shake each bottlevigorously for 1 minute.

6. Using a plastic funnel andfilter paper, filter the contentsof the bottle into anotherround sample bottle.

7. Analyze this extract fornitrate-nitrogen within 2hours. If this is not possible,then the extract may berefrigerated for 24 hoursbefore analysis. Note: The colorimetric test fornitrate-nitrogen is temperaturesensitive. If the extract has beenrefrigerated, allow it to return toroom temperature before analyzing.


Analyze withintwo hours

9

CALCIUM SULFATE EXTRACTION, continued

REAGENTSDescription Cat. No.Calcium Sulfate Powder, 20 grams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12321-20

APPARATUSBottle, Mixing, Round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18624-00Cylinder, Graduated, Polymethylpentene, 25 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Filter Paper, Circular, 15 cm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506-58Funnel, Polyethylene, 82 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24155-82Measuring Spoon, 0.1 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511-00Soil Scoop, 5.0 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-05Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00

10

The Mehlich 2 Soil Extractant is used for extracting calciumand magnesium, phosphorus, and potassium from soils. It issuitable for most classes of soils. With highly calcareous soils,calcium and magnesium results will be artificially high.

Before extraction, dry the soil sample, then screen it to afineness of 0-2 mm using the Hach Soil Sieve in the kit.Careful preparation is important to assure volumetricmeasurement of the soil sample. Refer to the introductorysections for soil sampling and sample preparation.

PREPARING THE MEHLICH 2 EXTRACTANTPrepare the Mehlich 2 Soil Extractant as follows:

1. Measure 20 ml of the Mehlich 2 Soil Extractant Concentrateinto a 25-ml graduated cylinder.

2. Transfer the extractant concentrate to one of the flip-topdispensing bottles provided.

3. Add deionized water to the dispensing bottle until the volumereaches the bottom of the neck. Invert several times to mix.

4. Using the laboratory pen, label the bottle with the extractantname to avoid confusion when working with other extractants.The Mehlich 2 Soil Extractant is now ready for use.

Mehlich 2 Extraction For SoilUsed for: Calcium + Magnesium, Phosphorus, Potassium

MEHLICH 2 EXTRACTION PROCEDURE

1. Using a 2-gram scoop,measure 1 scoop of theprepared soil sample into around sample bottle.

2. Using a 25-mL graduatedcylinder, accurately measure20 mL of the diluted Mehlich2 Soil Extractant into thecylinder, then transfer it to theround sample bottle.

3. Repeat steps 1–2 for eachsoil sample undergoingextraction. Note: To prevent confusion whenworking with several samples, labeleach sample bottle with the sample ortest name.

4. Cap and shake each bottlefor 5 minutes.


11

MEHLICH 2 EXTRACTION, continued

REAGENTSDescription Cat. No.Soil Extractant Concentrate, Mehlich 2, 1 L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22663-53

APPARATUSBottle, Mixing, Round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18624-00Bottle, Polyethylene with Cap, 200 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5909-00Cylinder, Graduated, Polymethylpentene, 25 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Filter Paper, Circular. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506-58Funnel, Polyethylene, 82 mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24155-82Soil Scoop, 2 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-02Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00Sprinkler, with screen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5912-00


6. Use this filtered extract forcalcium + magnesium,phosphorus, and potassium,analysis.Note: The filtered Mehlich 2 SoilExtract is stable for approximately 24hours. If stored longer, refrigerate toprevent microbial growth.

Note: The volume of extract obtainedfrom the filtration should be adequatefor the analysis of calcium +magnesium, phosphorus andpotassium.

Use for:CalciumMagnesiumPhosphorusPotassium

12

Potassium Chloride Extraction For SoilUsed For: Total Exchangeable Acidity

The Potassium Chloride Extraction is used to prepare the soilsample for total exchangeable acidity determination.


PREPARING THE POTASSIUM CHLORIDEEXTRACTANTTo prepare an approximate 1.0 N KCl solution:

1. Add three 5-gram scoops of potassium chloride salt to one ofthe flip-top dispensing bottles.

2. Add deionized water to the dispensing bottle until the volumereaches the bottom of the neck.

3. Invert the bottle several times to mix.

4. Using the laboratory pen, label the bottle with the extractantname to avoid confusion when working with other extractants.This is enough KCl solution for 4 tests.

1. Place a filter into a funneland moisten it with deionizedwater. Place a 125-mLerlenmeyer flask under thefunnel to collect the filtrate.

2. Using a 5-gram scoop,measure 1 scoop of theprepared soil sample into thefunnel containing the wettedfilter paper.

3. Using the 50 ml graduatedcylinder, slowly add 50 mL of1.0 N KCl solution to the soilsample in 10-mL incrementsover a 2 hour period. Afterthe addition is complete, rinsethe soil sample twice with10 mL of deionized water.Collect all of the filtrate fromthis step in the 125-mLerlenmeyer flask.

4. Repeat steps 1–3 for eachsoil sample undergoingextraction. Note: To prevent confusion whenworking with several samples, labeleach flask with the sample or testname.

POTASSIUM CHLORIDE EXTRACTION PROCEDURE


13

POTASSIUM CHLORIDE EXTRACTION, continued

5. Add water to the 125 mLerlenmeyer flask to about the75 mL mark. Use this filtratefor the determination of totalexchangeable acidity.

REAGENTSDescription Cat. No.Potassium Chloride, 454 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764-01

APPARATUSBottle, Polyethylene with Cap, 200 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5909-00Cylinder, Graduated, Polymethylpentene, 50 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-41Filter Paper, Circular. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506-58Flask, Erlenmeyer, Polymethylpentene, 125 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20898-43Funnel, Polyethylene, 82 mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24155-82Soil Scoop, 5 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-05Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00

14

Saturated Calcium Sulfate Extraction For SoilUsed For: Gypsum Requirement and Exchangeable Sodium

This procedure prepares the sample for determination ofgypsum requirement. By calculation, the analyst can alsoestimate the meq/100 grams of exchangeable sodium in the soil.The procedure is based on the principle that the calcium ions inthe saturated solution of CaSO4 will replace the exchangeablesodium in the extract. The number of milliequivalents ofsodium displaced will equal the number of Ca2+

milliequivalents extracted from the saturated CaSO4 solution.


PREPARING THE SATURATED CALCIUMSULFATE EXTRACTANT1. Using the 1-gram soil level scoop, add one level scoop ofcalcium sulfate to a flip-top dispensing bottle.

2. Add deionized water to the dispensing bottle until the volumereaches the bottom of the neck.

3. Shake the solution vigorously several times over a 30 minuteperiod to dissolve the calcium sulfate. A small amount of thecalcium sulfate may not dissolve.

4. Using the laboratory pen, label the bottle with the extractantname to avoid confusion when working with other extractants.

CALCIUM SULFATE EXTRACTION PROCEDURE

1. Using the 1-gram soilscoop, measure 1 scoop of theprepared soil sample into around sample bottle.

2. Using a 25-ml graduatedcylinder, accurately measure20 mL of the saturatedcalcium sulfate solution, andtransfer it to the round samplebottle containing the soilsample.

3. Repeat steps 1-2 for eachsoil sample undergoingextraction.Note: To prevent confusion whenworking with several samples, labeleach sample bottle with the sample ortest name.

4. Cap and shake each bottlefor 1 minute at 10 minuteintervals over a 30 minuteperiod.


15

SATURATED CALCIUM SULFATE EXTRACTION, continued


6. Use this filtered extract forthe determination of gypsumrequirement andexchangeable sodium.

REAGENTSDescription Cat. No.Calcium Sulfate, 20 grams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12321-20

APPARATUSBottle, Mixing, Round . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18624-00Bottle, Polyethylene with Cap, 200 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5909-00Cylinder, Graduated, polymethylpentene, 25 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Filter Paper, Circular. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 506-58Funnel, Polyethylene, 82 mm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24155-82Soil Scoop, 1 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-01Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00

Use for:gypsum requirementexchangeable sodium

11

SMP Buffer Extraction For SoilUsed For: Lime Requirement

The SMP Buffer Extraction is designed for soils with large limerequirements and large reserves of exchangeable aluminum(Al). The procedure may be inappropriate for:

• low lime requirement soils (< 2 tons/ acre or 2,240 kg/Ha) • soils containing organic matter greater than 10%• sandy soils• soils with high levels of kaolinite and hydroxy oxides of

aluminum and iron in their clay fractions.

The analysis of total exchangeable acidity may be moreeffective for determining the lime requirement in soils notsuitable for the SMP Buffer method.


SMP BUFFER EXTRACTION PROCEDURE

1. Using a 2-gram soil scoop,measure 4 scoops of theprepared soil sample into a50-mL beaker.

2. Using the 25-mLgraduated cylinder, accuratelymeasure 21 mL of deionizedwater and transfer it to the 50-mL beaker.

3. Repeat steps 1–2 for eachsoil sample undergoingextraction. Note: To prevent confusion whenworking with several samples, labeleach beaker with the sample or testname.

4. Add the contents of oneLime Requirement BufferPillow to each 50-mL beaker.


12

SMP BUFFER EXTRACTION, continued

5. Using the spatula, stir thecontents of the beaker for 1minute and allow it to standfor 10 minutes.Note: Rinse spatula with deionizedwater before stirring each sample.

6. After 10 minutes, use theprepared sample for limerequirement determination.

REAGENTS Description Cat. No.Lime Requirement Buffer Powder Pillows, 25/pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14345-98

APPARATUSBeaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41Cylinder, Graduated, Polymethylpentene, 25 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Soil Scoop, 2 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-02Soil Sieve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46159-00Spatula, Stainless Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 561-62

10 minutes

18

SECTION 4 SOIL ANALYSIS PROCEDURES

Calculation Of Cation Exchange Capacity and Percent Base Saturation in Soil

The calculation of cation exchange capacity and percent basesaturation requires previous determination of potassium,calcium + magnesium, sodium, and lime requirement.

Determining the cation exchange capacity (CEC) of soils isimportant for assessing supplemental potassium needs and theappropriate quantity of herbicides to apply to soils. Precisedetermination of CEC is time consuming. Soil testing labs inregions with acidic to neutral (pH 7) soils have determinedthat estimating the CEC by summing the exchangeable K, Ca,Mg, and neutralizable acidity (lime requirement) is acceptable(see equation below). Measurement of CEC for calcareoussoils (pH >7) may be inflated by the CaCO3 in the Mehlich 2extract.

CEC meq/100 grams =

K + Ca + Mg + Na + ( SMP Lime Requirement x 2 )

The values for K, Ca, Mg, and Na are in meq/100 g, not in ppm.Refer to the individual procedures to insure the proper units.See the Gypsum Requirement procedure for calculating the Navalue.

Rarely would summation include a numeric value for both Naand exchangeable acidity. Acidic soils have a lime requirementand are typically low enough in sodium that its value isinsignificant in the CEC calculation. Soils that are alkalinehave no lime requirement value and therefore the value shouldnot be included in the calculation.

[K + Ca + Mg + Na] x 100_____________________% Base Saturation =

CEC

Note: Cation values , K, Ca + Mg, Na must be as meq/100 g

19

1. Obtain a calcium sulfateextract for the soil sample byperforming the SaturatedCalcium Sulfate Extractionprocedure in Section 3.

2. Using a 1.0-mL dropper,accurately transfer 1.0 mL ofthe sample extract prepared inStep 1 to a 50-mL erlenmeyerflask.

3. Add deionized water toabout the 25-mL mark.

4. Add 1.0 mL of BufferHardness 1 solution to theflask and swirl to mix.

Gypsum Requirement For SoilEDTA Titration Method

PROCEDURE

5. Add 3 to 4 drops ofManVer Hardness IndicatorSolution to the flask and swirlto mix.

6. Titrate the sample byadding 0.0075 N EDTAStandard Solution dropwise tothe flask while swirling.Keep an accurate count of thenumber of drops being addedto the solution. Continuetitrating until the color beginsto change from wine red topure blue.Note: If the sample contains highamounts of copper, the solution willreach endpoint without turning pureblue. If this happens, add titrantdropwise until no color change isvisible.

7. Calculate the gypsumrequirement using thecalculations following thesesteps.Note: If the number of drops of titrantare equal to or greater than 56, thenno gypsum requirement exists.

8. When analysis iscomplete, rinse the labwarewith deionized water.

Perform aCaSO4 Extraction

20

GYPSUM REQUIREMENT, continued

CALCULATIONSGypsum Requirement (GR), (meq/100 gms) =

28 – No. of Drops x 2___________2

Gypsum Requirement (Tons/Acre) =

GR meq per 100 grams x 1.7

Gypsum Requirement (Metric Tons/Ha) =

GR meq per 100 grams x 3.81

Estimated Exchangeable Sodium (meq/100 grams) =

[ 0.96 + (0.99 X GR meq per 100 grams)]

ExampleThe analyst titrates 1.0 mL of saturated solution and it requires50 drops of EDTA to obtain the endpoint.

GR, meq/100 gms = 28 – 50 x 2 = 6 meq/100 grams__2

GR, Tons/Acre = 6 X 1.7 = 10.2 tons/acre

GR, Kg/Ha = 6 X 3.81 = 22.86 metric tons/hectare

Est. Na meq/100 gms = [0.96 + (0.99 X 6)] =

6.9 meq/100 gms

REAGENTSDescription Cat. No.EDTA Standard Solution, 0.0075 N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24981-32Hardness 1 Buffer, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424-32ManVer Hardness Indicator Solution, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425-32

APPARATUSDropper, Glass, 5/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14197-05Flask, Erlenmeyer, Polymethylpentene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20898-41

[ ]( )( )[ ]

21

Calcium + Magnesium in SoilEDTA Titration Method

5. Add 3–4 drops of ManVerHardness Indicator Solutionto the flask and swirl to mix.If calcium and/or magnesiumis present, the solution willturn wine red.

6. Titrate the sample byadding 0.0075 N EDTAStandard Solution dropwise tothe flask while swirling.Keep an accurate count of thenumber of drops added to thesolution. Continue titratinguntil the color begins tochange from wine red toviolet.

7. As the endpoint isapproached, add titrant onedrop at a time; swirl after eachdrop. Continue this until adrop of titrant no longerresults in a visible colorchange. This is the endpointof the titration. Record thetotal number of drops requiredto reach the endpoint. Thesolution will be blue orslightly violet. Note: If the sample containssignificant amounts of copper thesolution will reach endpoint withoutturning pure blue. If this occurs, addtitrant dropwise until no color changeis visible.

8. Divide the number ofdrops of titrant by 2 todetermine the meq/100 gramsof calcium + magnesium.

1. Obtain a Mehlich 2 extractfor the soil sample byperforming the Mehlich 2Extraction procedure inSection 3.

2. Using a 1.0-mL dropper,accurately transfer 1.0 mLof the sample extract fromStep 1 into a 50-mLerlenmeyer flask.

3. Add deionized water toabout the 25-mL mark.

4. Add 1.0 mL of BufferHardness 1 Solution to theflask and swirl to mix.

PROCEDURE

Perform aMehlich 2Extraction

Calcium + Magnesiummeq/100 grams =

No. of Drops__________2

22

CACLIUM AND MAGNESIUM, continued


REAGENTSDescription Cat. NoBuffer Solution, Hardness 1, 100 mL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424-32EDTA Standard Solution, 0.0075 N. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24981-32ManVer Hardness Indicator Solution, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425-32

APPARATUSDropper, Glass, 5/pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14197-05Flask, Erlenmeyer, Polymethylpentene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20898-41

23

Lime Estimation, Free (Excess) in SoilA calcareous soil is alkaline in pH because it contains calciumcarbonate particles. Calcareous soils effervesce (fizz) whentreated with 2.5 N hydrochloric acid (HCl). The degree ofeffervescence determines whether the soil is non-calcareous,slightly, moderately, or highly calcareous.

Calcareous soils present several problems to crop management.While the soils are highly buffered against acidity (high % basesaturation), the alkaline pH reduces the availability ofphosphorus, iron, zinc, manganese, copper and boron.

1. Using a 1-g scoop,measure 1 scoop of theprepared soil sample ontothe watch glass provided.Note: Several samples may beanalyzed on the watch glass. Use thelaboratory pen to divide the watchglass into sections and carefully labeleach section. Use one section persample Use care to prevent crosscontamination between samples.

2. Add deionized waterdropwise to the soil until it isminimally saturated. Thisexpels air from the sample,preventing erroneous results.

3. Repeat steps 1–2 for eachsoil sample undergoinganalysis.

4. Add 3 drops of 2.5 N HClto each soil sample and notethe degree of effervescence.Note: It is helpful when first learningthis procedure to test several soils ofknown pH and/or lime content to useas references.

PROCEDURE

5. Record whether the soil isnon-calcareous, slightly,moderately, or highlycalcareous.


24

LIME ESTIMATION, continued

REAGENTSDescription Cat. No.Hydrochloric Acid Standard Solution, 2.5 N, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418-32

APPARATUSPen, Laboratory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20920-00Soil Scoop, 1 g . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22628-01Watch Glass, Pyrex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 578-67

25

Lime Requirement for SoilElectrode Method

PREPARATIONCalibrate the Pocket Pal pH Tester according to the directionsbelow.

A. Prepare a pH 7.00 buffer solution by adding the contents ofone pH 7.00 Buffer Powder Pillow to a 50-ml beaker containing50 mL of water. Swirl the beaker until the contents aredissolved.

B. Slide the on/off switch located on the top of the Pocket PalpH Tester to on.

C. Remove the protective cap from the bottom of theinstrument and immerse the pH electrode tip one inch below thesurface of the buffer solution. If necessary, calibrate theinstrument by adjusting the calibration screw near the pocketclip with the trim tool (screwdriver) provided to obtain areading of 7.0.

1. Obtain a SMP bufferextract for the soil sample byperforming the SMP BufferExtraction procedure inSection 3.

2. Immerse the tip of thecalibrated Pocket Pal pHTester one inch below thesurface of the sample extractfrom Step 1 and stir gentlyuntil the soil is completelysuspended and the pH readingis stable.

3. Record the pH reading tothe nearest 0.1 pH unit. Thisis the buffer pH.

4. Rinse the pH electrodewith deionized water.Remove the excess by wipingthe tip with a tissue beforecontinuing to the next sample.

PROCEDURE

Perform aSMP BufferExtraction

26

LIME REQUIREMENT, continued

5. Once the pH of eachsample has been determined,rinse the electrode withdeionized water. Slide theon/off switch of the PocketPal pH Tester to off and coverthe electrode with theprotective cap before storing.

6. Refer to the LimeRequirement Table followingthese steps to determine theactual Lime Requirement ofthe sample by using theexperimentally obtainedbuffer pH value.

See LimeRequirement Table

The most common acceptable method of determining limerequirement is to measure pH on an SMP extraction of the soil.In this method, a buffer is added to an acidic soil. The responseof the soil, measured as an increase in pH, is related to the tonsof lime (as CaCO3) needed per acre to raise the soil pH to either6.5 or 7.0.

REAGENTSDescription Cat. No.Buffer Powder Pillows, pH 7, 50/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22270-66

APPARATUSBeaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41pH Pocket Pal Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44350-00

ON-OFF SWITCH

PROTECTIVECAP

27

LIME REQUIREMENT TABLETons/Acre of Pure Limestone* (as CaCO3) Required to Raise Buffer pH

Buffer pH To pH 7.0 To pH 6.56.8 0.1 0.16.7 0.7 0.66.6 1.2 1.06.5 1.9 1.66.4 2.7 2.36.3 3.4 2.96.2 4.2 3.66.1 5.1 4.36.0 5.7 4.85.9 6.7 5.75.8 7.5 6.45.7 8.4 7.15.6 9.1 7.75.5 9.8 8.35.4 10.7 9.15.3 11.5 9.85.2 12.4 10.55.1 13.1 11.1

The values in this table are based on tons of pure, fine CaCO3 with a calcium carbonate equivalent (CCE)of 100.If you wish to use limestone other than 100 CCE, then calculate the required tons as follows:

To determine the requirement of agricultural limestone or other lime materials, divide the numberobtained from the table by the assayed CCE, expressed as a decimal percentage.

For example: If your buffer pH is 6.6, and you wish to raise the soil pH to 7.0, then 1.2 tons/acre of100 CCE limestone should be incorporated into the top 8 inches of your soil. If the CCE of thelimestone you wished to apply is assayed at 87, then you would need to apply 1.2/0.87, or1.37 tons of that limestone to bring your soil to the desired pH.

29

Nitrate-Nitrogen in Soil (0-60 ppm)Cadmium Reduction Method

PREPARATIONPlace the High Range Nitrate Color Disc into the ColorComparator. Make sure it is inserted so the mg/L values arevisible through the window of the Color Comparator.

1. Obtain a calcium sulfateextract for the soil sample byperforming the CalciumSulfate Extraction procedurein Section 3.

2. Label 1 Color ViewingTube “S” for sample andanother Color Viewing Tube“B” for blank. Thoroughlyrinse both Color ViewingTubes with deionized water.Shake the tubes to remove theremaining rinse water.

3. Add a small amount of thesample extract (about 1/4"deep) to the Color ViewingTube marked “S”. Cap thetube with a rubber stopper andshake it for a few seconds.Discard this solution.

4. Add the extract to bothtubes until the meniscus iseven with the 5-mL mark(bottom of frosted area).

PROCEDURE

Perform aCa2SO4 Extraction

30

NITRATE-NITROGEN IN SOIL, continued

9. When analysis iscomplete, rinse the labwarewith deionized water. Shakedry. Store the color disc inthe plastic bag provided.

5. Add the contents of oneNitraVer 5 Powder Pillow tothe tube marked “S”. Cap andshake the tube vigorously forexactly one minute. Note: This kit contains a 15 mg/Lnitrate-nitrogen standard so theanalyst can learn proper shakingtechnique and use of the color wheel.It is suggested that the analystpractice with the standard untilrepeated results are within 1 mg/L ofeach other. The standard shouldread near 15 mg/L. If theexperimental concentration is lessthan 14 mg/L or greater than 17mg/L, repeat the procedure untilsatisfactory results are obtained.

6. Immediately place tubes“S” and “B” into thecomparator with tube “B” inthe outside hole and tube “S”in the inside hole.

7. Five minutes aftercompleting Step 6, hold theColor Comparator up to alight source. Rotate the discuntil the color in the windowfor tube “B” matches thecolor in the window for tube“S”. Record the value in thescale window. Take twomore readings of the sample,rotating the color discbetween each reading.Complete all three readingswithin 10 minutes ofcompleting Step 6.Note: Readings before 5 minutes orafter 10 minutes will result in aninaccurate value.

Note: It is very important that thestandard and the sample are viewedunder the same lighting conditions.

8. Take the average of thethree readings and multiply itby 2 for the available nitrate-nitrogen value in the soil.

Available NO3-N =(Average of 3 readings) x 2

31

NITRATE-NITROGEN IN SOIL, continued

REAGENTSDescription Cat. No.NitraVer 5 Nitrate Reagent Powder Pillows, 100/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14035-99

APPARATUSColor Comparator Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732-00Color Viewing Tube with Caps, Plastic, pk/4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46600-04Nitrate Nitrogen, High Range, Color Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14038-00

32

pH in SoilElectrode Method


A. Prepare a pH 7.00 buffer solution by adding the contents ofone pH 7.00 Buffer Powder Pillow to a 50-ml beaker containing50 mL of water. Swirl the beaker until the contents aredissolved.

B. Slide the on/off switch located on the top of the Pocket PalpH Tester to on.

C. Remove the protective cap from the bottom of theinstrument and immerse the pH electrode tip one inch below thesurface of the buffer solution. If necessary, calibrate theinstrument by adjusting the calibration screw near the pocketclip with the trim tool (screwdriver) provided to obtain areading of 7.

PROCEDURE

1. Obtain an aqueous extractfor the soil sample byperforming the AqueousExtraction procedure inSection 3.

2. Immerse the tip of thecalibrated Pocket Pal pHTester one inch below thesurface of the aqueous sampleextract and stir gently until thesoil is completely suspended.

3. Record the stabilized pHreading to the nearest 0.1 pHunit.

4. Rinse the pH electrodewith deionized water.Remove the excess by wipingthe tip with a tissue beforecontinuing to the next sample.

PerformAqueous

Extraction

33

pH IN SOIL, continued


APPARATUSBeaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41Pocket Pal pH Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44350-00Trim Tool (Screwdriver) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18933-00

5. Once the pH of eachsample has be determined,rinse the electrode withdeionized water. Slide theon/off switch of the PocketPal pH Tester to off andcover the electrode with theprotective cap before storing.

ON-OFF SWITCH

PROTECTIVECAP

34

Phosphorus in Soil (0-130 mg/L or 0-130 ppm)PhosVer 3 (Ascorbic Acid) Method

PREPARATIONPlace the Phosphate Color Disc into the Color Comparator.Make sure it is inserted so the mg/L values are visible throughthe window of the Color Comparator.

PROCEDURE

1. Obtain a Mehlich 2 extractfor the soil sample byperforming the Mehlich 2Extraction in Section 3.

2. Using the 2.5-mL dropper,add 2.5 mL of the filteredsample extract prepared inStep 1 to a 25-mL graduatedcylinder. Dilute to the 25 mLmark with deionized water,stopper, and invert to mix.


4. Add a small amount of thediluted extract (about 1/4"deep) to the Color ViewingTube marked “S”. Cap thetube with a rubber stopper andshake it for a few seconds.Discard this solution.


35

PHOSPHORUS IN SOIL, continued

5. Add the diluted Mehlich 2Extract to both tubes until themeniscus is even with the 5-mL mark on the tubes (bottomof frosted area).

6. Add the contents of onePhosVer 3 Powder Pillow tothe “S” tube. Cap and shakethe tube vigorously for oneminute.


8. Three minutes aftercompleting Step 6, hold theColor Comparator up to alight source. Rotate the discuntil the color in the windowfor tube “B” matches thecolor in the window for tube“S”. Record this value in thewindow. Take two morereadings for the sample,rotating the color discbetween each reading.Complete all three readingswithin 10 minutes ofcompleting Step 7.Note: Readings before 3 minutes orafter 10 minutes will result in aninaccurate value.

Note: It is very important that thesample is viewed under the samelighting conditions for all readings.

9. Take the average of thethree readings and multiplythis average by 3.3 for theavailable phosphate-phosphorus value in the soil.

10. When analysis iscomplete, rinse the colorviewing tubes with deionizedwater and store the color discin the plastic bag provided.

Available P-PO4 =(Average of 3 readings) X 3.3

36

PHOSPHORUS IN SOIL, continued

REAGENTSDescription Cat. No.PhosVer 3 Phosphate Reagent Powder Pillows, 100/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2209-99

APPARATUSColor Comparator Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732-00Color Viewing Tube with Caps, Plastic, pk/4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46600-04Dropper, Polyethylene, 2.5 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17045-00Phosphate, High Range, Color Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24898-00

37

Potassium (Exchangeable) in Soil (0-250 mg/L or 0-250 ppm)Turbidimetric Tetraphenylborate Method

5. Add the contents of onePotassium 3 Reagent PowderPillow. Firmly cap and shakethe cylinder vigorously for 10seconds. Allow the solutionto stand for at least 3 minutesbut no longer than 10 minutes.A white turbidity willdevelop.

6. While looking straightdown into the cylinder, slowlyinsert the Potassium Dip Stickvertically into the solutionuntil the black dot is no longervisible from above thecylinder.

7. Hold the dipstick in thatposition and rotate thecylinder so you can see thescale on the dipstick. Lookacross the surface of thesample to the scale on thedipstick. Record the number(in mm) on the dipstick scalewhere the surface of thesample meets the dipstickscale.

8. Repeat Steps 6-7 twomore times recording thevalue each time. Take theaverage of the three readings.Refer to the potassiumconversion table on thefollowing page to determinethe level of potassium in thesoil.

1. Obtain a Mehlich 2 extractfor the soil sample byperforming the Mehlich 2Extraction procedure inSection 3.

2. Using the 1-mL dropper,add 3.0 mL of the sampleextract from Step 1 to a 25-mlcylinder.

3. Add deionized water to the21-mL mark on the cylinder.Firmly cap the cylinder with a#3 rubber stopper, and invertto mix.

4. Add one Potassium 2Reagent Powder Pillow and3 mL of Alkaline EDTASolution to the cylinder. Capthe cylinder and invert severaltimes to mix. Allow thesolution to stand for at least3 minutes.


Repeat Steps6-7 twice

38

POTASSIUM (EXCHANGEABLE) IN SOIL, continued


POTASSIUM CONVERSION TABLE

DipstickReading mg/L (ppm) lbs/A Kg/Ha meq/100 g

mm Potassium Potassium Potassium Potassium

80 87 174 194 0.2275 94 188 210 0.2470 101 202 225 0.2665 109 218 243 0.2860 118 236 263 0.3055 129 258 281 0.3350 143 286 319 0.3745 159 318 355 0.4140 180 360 401 0.4635 207 414 462 0.5330 243 486 542 0.6225 294 588 656 0.75

REAGENTSDescription Cat. No.Alkaline EDTA Solution, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22687-32Potassium 2 Reagent, Solution Pillows, 25/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14322-98Potassium 3 Reagent Powder Pillows, 50/pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14323-96

APPARATUSCylinder, Graduated, Polymethylpentene, 25 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Dropper, Glass, 5/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14197-05Potassium Dipstick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45700-00Stopper, Neoprene, Solid, #3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14808-03

39

Salinity (Conductivity) in SoilElectrode Method

PREPARATIONA. Add 50 mL of the Saturated Calcium Sulfate ExtractionSolution used for the Calcium Sulfate Extraction procedure inSection 3 to a 50-mL plastic beaker.

B Slide the on/off switch on top of the Pocket Pal ConductivityTester to on.

C Remove the protective cap from the bottom of theinstrument. Immerse the electrode tip one inch below thesurface of the calcium sulfate extraction solution. If necessary,calibrate the instrument by adjusting the calibration screw nearthe pocket clip with the trim tool (screwdriver) provided.Adjust the value to 2200 µS. At 2200 µS, the display will read22 with a small 100 in the upper left hand corner.

1. Obtain an aqueous extractfor the soil sample byperforming the AqueousExtraction procedure inSection 3.

2. Immerse the tip of thecalibrated Pocket PalConductivity Tester one inchbelow the surface of thesample extract prepared inStep 1 and stir gently until thesoil is completely suspended.

Note: The range of the Pocket PalConductivity Tester is 100-19,900 µS.To obtain the proper value in µS/cm,multiply the large reading on PocketPal Conductivity Tester by the smallvalue (100) in the upper left handcorner of the display. This gives theconductivity value in µS/cm.However, the conductivity of soilsshould be expressed in mS/cm.Simply divide the large-sized readingby 10 to determine conductivity inmS/cm.

3. When the digital displaystabilizes, record the value.Divide the value in the displayby 10 to determine the mS/cmof conductivity. Note: If the larger display is 199 orgreater, the concentration of salt isgreater than the capacity of themeter. Dilute the suspension byadding an additional 20 mL ofdeionized water Multiplying the finalanswer by two. If this dilution resultsin a display reading that is still abovecapacity, additional 20 mL volumesshould be added until a suitablereading is obtained. For every 20 mLadded, add two to the multiplicationfactor (if a total 40 mL is added,multiply by 2; if a total 60 mL isadded, multiply by 3 and so on).

4. Rinse the electrode withdeionized water, and removethe excess by wiping the tipwith a tissue beforecontinuing to the next sample.Note: To maintain or improveperformance, periodically clean thestainless steel electrode by rinsing itin alcohol.

Perform anAqueous

Extraction

PROCEDURE

40

SALINITY IN SOIL, continued

5. Once the conductivity ofeach sample has beendetermined, rinse theelectrode with deionizedwater. Slide the on/off switchto off and cover the electrodewith the protective cap beforestoring.

APPARATUSDescription Cat. No.Beaker, 50 mL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41Pocket Pal Conductivity Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44375-00Trim Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18933-00

ON-OFF SWITCH

PROTECTIVECAP

41

Routine soil analysis usually includes an estimation of soiltexture. This method is used when exact proportions of sandsilt and clay are not needed or when equipment for mechanicalanalysis of soil is not available. While soil texture estimationrequires practice to become highly proficient, satisfactoryresults can be obtained by using the technique diagramed on thenext page and by referring to the modified textural trianglediagramed below. The procedure for estimation of soil texturewas developed at Kansas State University by Dr. DavidWhitney.

The modified version of the textural diagram below omits therare silt class and combines the loamy sand class with the sandyloam class. Other class boundaries are arranged in asymmetrical fashion that should be easily visualized andremembered.

The modified triangle consists of three tiers based on claycontent:

1. the CLAYS, those soils high in clay content are stronglycohesive and capable of being shaped into good ribbons.

2. the CLAY LOAMS which are intermediate in clay content,cohesiveness, and ribbon formation.

3. the LOAMS, or soils low enough in clay content so as toexhibit little or no cohesiveness and form poor or weak ribbons.The SANDS do not form ribbons.

The three tiers are each subdivided into three classes:

a. If silt is highly prominent, the prefix “silt” or “silty” is addedto form the categories on the right side of the triangle.

b. If sand is very prominent, the prefix “sandy” is added toform the categories on the left side of the triangle.

c. When neither sand nor silt predominates, the intermediatecategory is used without a prefix, as illustrated by the centralportion of the triangle.

Texture Estimation of Soil

DIAGRAM FOR ESTIMATING SOIL TEXTURE

43

Total Exchangeable Acidity in SoilNaOH Titration Method

PROCEDURE

1. Obtain a potassiumchloride extract for the soilsample by performing thePotassium ChlorideExtraction procedure inSection 3.

2. Add 5-6 drops ofphenolphthalein to theerlenmeyer flask containingthe sample extract prepared inStep 1. Swirl to mix.

3. Titrate the sample byadding 0.075 N NaOHStandard Solution dropwise tothe flask while swirling.Keep an accurate count of thenumber of drops of titrantbeing added to the solution. Continue titratinguntil the color begins tochange from colorless to lightpink.

4. As the endpoint isapproached, add titrant 1 dropat a time and swirl after eachdrop. Continue this until adrop of titrant results in a lightpink color that does notdisappear upon swirling. Thisis the endpoint of the titration.Record the total number ofdrops required to reach theendpoint of the titration.

5. Divide the number ofdrops of titrant by 10 todetermine the meq/100 g oftotal exchangeable acidity.This value is used todetermine the cationexchange capacity of acidicsoils as well as the limerequirement of highly acidicand weathered soils.

Perform aKCl

Extraction

Total ExchangeableAcidity (meq/100 g) =

No. of drops___________10

44

TOTAL EXCHANGEABLE ACIDITY, continued

CALCULATIONSTotal exchangeable acidity (TEA) is the amount ofexchangeable H+ and Al3+ in the soil, expressed in units ofmilliequivalents per 100 grams (meq/100 g).

TEA = drops of titrant/10

Lime requirement (LR) is the amount of 100% CCE (calciumcarbonate equivalents) CaCO3 needed to raise the soil pH to 6.5or to 7.0. LR is usually measured in units of tons/acre ortons/hectare. For every 1 meq/100 g of TEA determined byanalysis, you would need 1.12 metric tons of 100% CCECaCO3 per hectare to neutralize the acid.

LR (tons/acre) = TEA____2

LR (metric tons/Hectare) = TEA x 1.12

Sample calculations:

TEA = 16 drops of titrant / 10 = 1.6 meq/100 gLR (tons/acre) = 1.6 / 2 = 0.8 tons of CaCO3/acre

TEA = 22 drops of titrant / 10 = 2.2 meq/100 gLR (metric tons/hectare) = 2.2 x 1.12 =

2.46 metric tons of CaCO3/hectare

REAGENTSDescription Cat. No.Phenolphthalein Indicator Solution, 118 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162-37Sodium Hydroxide Titrant, 0.075 N, 118 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24980-37

APPARATUSFlask, Erlenmeyer, Polymethylpentene, 125 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20898-43

45

SECTION 5 IRRIGATION WATER ANALYSIS PROCEDURES

Conductivity in Irrigation WaterElectrode Method

1. Add approximately 30 mLof the sample to a 50-mLplastic beaker.

2. Immerse the tip of thecalibrated Conductivity Testerone inch below the surface ofthe sample and stir gently.

3. When the digital displaystabilizes, read and record thedisplay. The correct value inµS/cm (or µmhos/cm) isdetermined by multiplying thereading by the factordisplayed in the upper lefthand corner.

4. Rinse the electrode withdeionized water, and removethe excess by wiping the tipwith a tissue beforecontinuing to the next sample.

Note: To maintain or improveperformance, periodically clean thestainless steel electrode by rinsing itin alcohol.

PREPARATIONA. Add 50 mL of the saturated Calcium Sulfate ExtractionSolution used for the Calcium Sulfate Extraction procedure inSection 3 to a 50-mL plastic beaker.

B. Slide the on/off switch on top of the Pocket PalConductivity Tester to on.

C. Remove the protective cap from the bottom of theinstrument. Immerse the electrode tip one inch below thesurface of the calcium sulfate extraction solution. If necessary,calibrate the instrument by adjusting the calibration screw nearthe pocket clip with the trim tool (screwdriver) provided.Adjust the value to 2200 µS. At 2200 µS, the display will read22 with a small 100 in the upper left hand corner.

PROCEDURE

46

CONDUCTIVITY IN IRRIGATION WATER, continued

5. Once the conductivity ofeach sample has beendetermined, rinse theelectrode with deionizedwater. Slide the on/off switchto off and cover the electrodewith the protective cap beforestoring.

APPARATUS Cat. No.Beaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41Pocket Pal Conductivity Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44375-00

ON-OFF SWITCH

PROTECTIVECAP

47

Calcium + Magnesium in Irrigation WaterEDTA Titration Method

1. Using the table below andthe conductivity of theanalyzed water sample,determine the amount ofsample to titrate in thisprocedure.

2. Using either a 1.0-ml or a2.5-ml dropper, accuratelytransfer the amount of waterdetermined in the table to a50-mL erlenmeyer flask. Addabout 25 mL deionized waterto the flask.

3. Add 1.0 mL of BufferHardness 1 solution to theflask. Swirl to mix.

4. Add 3 to 4 drops ofManVer Hardness IndicatorSolution to the flask and swirlto mix. If calcium and/ormagnesium is present, thesolution will have a wine redcolor.

PROCEDURE

Conductivity µS/cm mL of Water To Titrate

>2000 mS/cm 1.0 mL<2000 mS/cm 2.5 mL

See Table

48

CALCIUM + MAGNESIUM IN IRRIGATION WATER, continued

5. Titrate the sample byadding 0.0075 N EDTAStandard Solution dropwise tothe flask while swirling.Keep an accurate count of thenumber of drops being addedto the solution. Continuetitrating until the color beginsto change from wine red toviolet.

6. As the endpoint isapproached, add 1 drop oftitrant at a time and swirl.Continue this until a drop oftitrant no longer results in avisible color change. This isthe endpoint of the titration.Record the total number ofdrops required to reach theendpoint of the titration. Thesolution will be pure blue.

Note: If the sample contains highamounts of copper, the solution willreach endpoint without turning pureblue. If this occurs, add drops oftitrant until no color change isvisible.

7. Determine the meq/L ofCa + Mg using the formulaabove.

Example: The conductivityof a water sample wasdetermined to be 1450 S/cm.The analyst titrates 2.5 mL ofthe irrigation water sample.The total number of drops toreach the endpoint was 50.The meq/L Ca + Mg iscalculated as follows:

meq/L Ca + Mg =

50_____ =2 x 2.5

50___ =5

10 meq/L of Ca + Mg

8. When analysis iscomplete, rinse the glasswarewith deionized water. Shakedry.

REAGENTSDescription Cat. No.Hardness 1 Buffer, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424-32ManVer Hardness Indicator Solution, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425-32EDTA Standard Solution, 0.0075 N, 100 mL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24981-00

APPARATUSCylinder, Graduated, Polymethylpentene, 25 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Flask, Erlenmeyer, Polymethylpentene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20898-41

Ca + Mg meq/L =

Drops of Titrant________________(2 x mL of sample)

49


2. Add a small amount of thewater sample (about 1/4"deep) to the Color ViewingTube marked “S”. Cap thetube with a rubber stopper andshake it for a few seconds.Discard this solution.

3. Add the water sample toboth tubes until the meniscusis even with the 5-mL markon the tubes (bottom of thefrosted area).

4. Add the contents of oneNitraVer 5 Powder Pillow tothe tube marked “S”. Cap andshake the tube vigorously forexactly one minute.

Note: This kit contains a 15 mg/Lnitrate-nitrogen standard so theanalyst can learn proper shakingtechnique and use of the color wheel.It is suggested the analyst practicewith the standard until repeatedresults are within 1 mg/L of eachother. The standard should read near15 mg/L. If the experimentalconcentration is less than 14 mg/L orgreater than 17 mg/L, repeat theprocedure until satisfactory resultsare obtained.

Nitrate Nitrogen in Irrigation Water (0-50 mg/L)Cadmium Reduction Method

PREPARATIONPlace the High Range Nitrate Color Disc into the ColorComparator. Make sure it is inserted so the mg/L values arevisible through the window of the Color Comparator.

PROCEDURE

50

NITRATE NITROGEN IN IRRIGATION WATER, continued


6. Five minutes aftercompleting Step 5, hold theColor Comparator up to alight source. Rotate the discuntil the color in the windowfor tube “B” matches thecolor in the window for tube“S”. Record the value in thewindow. Take two morereadings for the sample,rotating the color discbetween each reading.Complete all three readingswithin 10 minutes ofcompleting Step 5.

Note: Readings before 5 minutes orafter 10 minutes will result in aninaccurate value.

Note: It is very important that theblank and the sample are viewedunder the same lighting conditions.

7. Take the average of thethree readings to determinethe mg/L NO3-N in thesample.

8. When analysis iscomplete, rinse the colorviewing tubes with deionizedwater and store the color discin the plastic bag provided.

REAGENTSDescription Cat. No.NitraVer 5 Nitrate Reagent Powder Pillows, 100/pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14035-99

APPARATUSColor Comparator Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732-00Color Viewing Tube with caps, plastic, pk/4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46600-04Nitrate Nitrogen, High Range, Color Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14038-00

NO3–N =(Average of 3 readings)

51

pH in Irrigation WaterElectrode Method

1. Add approximately 40 mLof the water sample to a 50-mL plastic beaker.

2. Immerse the tip of thecalibrated Pocket Pal pHTester one inch below thesurface of the sample and stirgently.

3. Record the stabilized pHreading to the nearest 0.1 pHunit.

4. Rinse the electrode indeionized water. Remove theexcess by wiping the tip witha tissue before continuing tothe next sample.


A. Prepare a pH 7.00 buffer solution by adding the contents ofone pH 7.00 Buffer Powder Pillow to a 50-ml beaker containing50 mL of water. Swirl the beaker to dissolve the contents.

B. Slide the on/off switch located on top of the Pocket Pal pHTester to on.

C. Remove the protective cap from the bottom of theinstrument and immerse the electrode tip one inch below thesurface of the solution. If necessary, calibrate the instrument byadjusting the calibration screw near the pocket clip with thetrim tool (screwdriver) provided to obtain a reading of 7.0.

PROCEDURE

52

pH IN IRRIGATION WATER, continued


APPARATUSBeaker, Polypropylene, 50 ml . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1080-41pH Pocket Pal Tester . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44350-00

5. After determining the pHof each sample, rinse theelectrode with deionizedwater. Slide the on/off switchto off and cover the electrodewith the protective cap beforestoring.

ON-OFF SWITCH

PROTECTIVECAP

53

Phosphorus in Irrigation Water (0-5 mg/L)PhosVer 3 (Ascorbic Acid) Method


2. Add a small amount of thewater sample (about 1/4"deep) to the Color ViewingTube marked “S”. Cap thetube with a rubber stopper andshake it for a few seconds.Discard this solution.

3. Add the water sample toboth tubes until the meniscusis even with the 5-mL markon the tubes (bottom of thefrosted area).

4. Add the contents of onePhosVer 3 Powder Pillow tothe “S” tube. Cap the tubeand shake vigorously for 15seconds.

PREPARATIONPlace the High Range Phosphate Color Disc into the ColorComparator. Make sure it is inserted so the mg/L values arevisible through the window of the Color Comparator.

PROCEDURE

54

PHOSPHORUS IN IRRIGATION WATER, continued


6. Three minutes aftercompleting Step 6, hold theColor Comparator up to alight source. Rotate the discuntil the color in the windowfor tube “B” matches thecolor in the window for tube“S”. Record the value in thewindow. Take two morereadings for the sample,rotating the color discbetween each reading.Complete all three readingswithin 10 minutes ofcompleting Step 6.

Note: Readings before 3 minutes orafter 10 minutes will result in aninaccurate value.

Note: It is very important that theblank and the sample are viewedunder the same lighting conditions.

7. Take the average of thethree readings. Divide thisvalue by 10 to obtain themg/L PO4 in the sample.To convert the reading to Pdivide the PO4 value by 3.1.

8. When analysis iscomplete, rinse the colorviewing tubes with deionizedwater. Shake dry. Store thecolor disc in the plastic bagprovided.

REAGENTSDescription Cat. No.PhosVer 3 Phosphate Reagent Powder Pillows, 100/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2209-99

APPARATUSColor Comparator Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1732-00Color Viewing Tube with caps, plastic, pk/4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46600-04Phosphate, High Range, Color Disc. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24898-00

PO4 (mg/L) = Average of 3 Readings____________________

10PO4 (mg/L)__________P =

3.1

PROCEDURE1. Determine the concentration of total soluble salts in meq/Lby dividing the conductivity µS/cm by 100.

Note: Refer to the procedure in this section for determining the conductivity ofirrigation water.

2. Determine the Ca + Mg (meq/L) by the EDTA TitrationMethod.

Note: Refer to the procedure in this section for the determination of calcium +magnesium in irrigation water.

3. Subtract the value in step 2 from the value in step 1. This isthe estimated sodium in meq/L.

Sodium Estimation =

Conductivity (µS/cm) – (Calcium + Magnesium)_________________100

SAMPLE CALCULATIONS a. A water sample has a conductivity value of 1250 µS/cm.Calcium + Magnesium meq/L was determined to be 8.6.

b. Sodium Estimation (meq/L) = 1250 – 8.6 = 3.9 meq/L____100

c. SAR =

Sodium Estimation (meq/L) = 3.9_____________________ ______

Ca + Mg (meq/L) 8.6_____________ ___2 2

d. SAR = 3.9 = 3.9 / 2.07 = 1.9______

4.3√√√

55

Sodium Estimation & Sodium Adsorption Ratio Calculations(Na meq/L) for Irrigation Water

( )

56

ORDERING AND TECHNICAL ASSISTANCE

For current price information, technical assistance, or orderingassistance, contact the Hach office or authorized distributorserving you.

Hach Company World HeadquartersP.O. Box 389Loveland, Colorado 80539 U.S.A.Telephone: 303-669-3050 or 800-227-4224 (U.S. callers only)FAX: 303-669-2932E-mail: [email protected]

INFORMATION REQUIRED:• Hach account number (if available)• Billing address• Shipping address• Your name and phone number• Purchase order number• Catalog number(s)• Brief description or model number• Quantity

CLAIMSWe take extreme care to fill and pack orders properly. If anerror or damage occurs, report shipping damage to the carrierimmediately and contact Hach Customer Service as soon aspossible (always within two weeks of receipt). The toll-freenumber is 800-227-4224 in the United States.

RETURN OF ITEMSAuthorization must be obtained from Hach before returningitems for any reason. For credit or replacement, call HachWorld Headquarters or Hach Europe at the listed telephonenumbers.

TECHNICAL ASSISTANCEHach Company offers free technical assistance to owners orprospective owners having questions about test methods,equipment or applications. Training workshops and seminarsare offered to help owners fine-tune their technique and gainconfidence in their test results. For more information, callHach’s toll-free help line 1-800-227-4224 in the United Statesor contact your distributor.

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