NPK-1 SOIL KIT MANUAL - Hach Company

NPK-1 SOIL KIT MANUAL

7/92 1ED, rev1 11/01 rb

©Hach Company, 1992-2001. All rights are reserved. Printed in U.S.A.

24959-88

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TABLE OF CONTENTS

PagePREFACEReferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

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 and Screening Soil Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Filtering Soil Extracts. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Obtaining Water Samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

SECTION 3 SOIL EXTRACTION PROCEDURESAqueous Extraction (for pH) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Calcium Sulfate Extraction (for nitrate-nitrogen) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8Mehlich 2 Extraction (for phosphorus & potassium) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

SECTION 4 SOIL ANALYSIS PROCEDURESNitrate-Nitrogen—Cadmium Reduction method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12pH—Electrode method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Phosphorus—Ascorbic Acid method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17Potassium, Exchangeable— Turbidimetric Tetraphenylborate method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Texture Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

SECTION 5 IRRIGATION WATER ANALYSIS PROCEDURESNitrate-Nitrogen—Cadmium Reduction method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24pH— Electrode method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26Phosphorus— Ascorbic Acid method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28Ordering and Technical Assistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

iv

NPK-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 classrooms 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 the professionalscientist and non-scientist 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 recommendations from a competent full servicesoil laboratory.

When possible, Hach Company used proven and acceptedmethodology in this kit. The basis of the procedures in thismanual were taken from the following books and publications.

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.Madison, Wisconsin1991

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. NPK-1 Soil Kit Manualcontains directions for performing the analyses. This manualhas been printed on special waterproof, tear-resistant paper.

Hach Soil and Irrigation Water Interpretation Manual helpsinterpret 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.

Using This ManualThis manual is arranged in sequential sections. The first sectionacquaints the reader with some of the equipment and analyticaltechniques used with the equipment. 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 solution. Theanalysis is then completed on the solution containing thesubstance.

This manual contains three 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 on a sample may be necessary.

EXTRACTION GUIDE

Aqueous Extraction Calcium Sulfate Extraction↓ ↓

pH Nitrate-Nitrogen

Mehlich 2 Extraction Potassium Chloride Extraction↓ ↓

PhosphorusPotassium

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.

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.

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.

5. After 30 minutes, use theprepared sample for pHdetermination.

6

SECTION 3 SOIL EXTRACTION PROCEDURES

Use the Aqueous Extraction to prepare the soil sample for pH.The soil suspension does not need to be filtered to determinepH—measurements are 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.

1. Using a 5-gram scoop,measure 4 scoops of theprepared soil sample into a50-mL plastic beaker.

2. Using the 25-mLgraduated cylinder, accuratelymeasure 20 mL of deionizedwater and transfer it to the 50-mL beaker.

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

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

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: pH

AQUEOUS EXTRACTION PROCEDURE

Repeat for each sample

30 minutes

7

AQUEOUS EXTRACTION

APPARATUSDescription Cat. 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

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.

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

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

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

3. Using the 25-mLgraduated cylinder, accuratelymeasure 20 mL of deionizedwater and transfer it to theround mixing bottle.


8

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

Before extraction, dry the soil sample, then screen it to afineness 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 For SoilUsed for: Nitrate-Nitrogen

CALCIUM SULFATE EXTRACTION PROCEDURE

Repeat Steps 1–3for each sample

Analyze withintwo hours

9

CALCIUM SULFATE EXTRACTION

REAGENTSDescription Cat. No.Calcium Sulfate, 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 phosphorusand potassium from soils. It is suitable for all classes of soils.

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 2EXTRACTANTPrepare 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 bottle 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. The Mehlich 2 Soil Extractant is now ready for use.

Mehlich 2 Extraction For SoilUsed For: Phosphorus, Potassium

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.


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

4. Cap and shake each bottlefor 5 minutes.

MEHLICH 2 EXTRACTION PROCEDURE

Repeat Steps 1–2for each sample

11

MEHLICH 2 EXTRACTION

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

6. Use this filtered extract forphosphorus and potassiumanalysis.

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 phosphorus andpotassium.

REAGENTSDescription Cat. No.Soil Extractant Concentrate, Mehlich 2, 500 mL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22663-49

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

Use for PO4–

and K+ analysis

12

SECTION 4 SOIL ANALYSIS PROCEDURES

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

1. Obtain a calcium sulfateextract of the soil sample byperforming the CalciumSulfate Extraction procedureon page 8.

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 theextract (about 1/4" deep) tothe Color Viewing Tubemarked “S”. Cap the tubewith 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 the frosted area).

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

Perform CaSO4extraction

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

13

NITRATE NITROGEN IN SOIL

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 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 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.

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

14

NITRATE NITROGEN IN SOIL

REAGENTSDescription Cat. No.NitraVer 5 Nitrate Reagent Powder Pillows, 100/pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14035-99Nitrogen Stock Solution, 15 mg/l, 118 ml MDB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24252-37

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

15

pH in 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 thesolution surface. If necessary, calibrate the instrument byadjusting the calibration screw near the pocket clip with thetrim tool (screwdriver) provided to obtain a reading of 7.

PROCEDURE

1. Obtain an aqueous extractfor the soil sample byperforming the AqueousExtraction procedure on page6.

2. Immerse the tip of thePocket Pal pH Tester one inchbelow the surface of theaqueous sample extract andstir gently until the soil iscompletely 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.

Perform anAqueous

Extraction

16

pH IN SOIL

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

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

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 andcover the electrode with theprotective cap before storing.

17

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

1. Obtain a Mehlich 2 extractof the soil sample byperforming the Mehlich 2Extraction procedure on page10.

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 tightly and invert tomix.


4. Add a small amount of thediluted extract (about 1/4”deep) prepared in Step 2 tothe Color Viewing Tubemarked “S”. Cap the tubewith a rubber stopper andshake it for a few seconds.Discard this solution.

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

Perform aMehlich 2Extraction

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.

18

PHOSPHORUS IN SOIL

5. Add the diluted Mehlich 2Extract from Step 2 to bothtubes until the meniscus iseven with the 5-mL mark onthe tubes (bottom of thefrosted 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.



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

19

PHOSPHORUS IN SOIL

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

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

5. Add the contents of onePotassium 3 Reagent PowderPillow. Firmly stopper thecylinder and shake vigorouslyfor 10 seconds. Allow thesolution to stand for at least 3minutes but no longer than 10minutes. A white turbiditywill develop.

6. While looking straightdown into the cylinder, slowlyinsert the Potassium Dip Stickinto the solution until theblack dot is no longer visiblefrom above the cylinder.

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 step 6–7 two moretimes recording the value eachtime. Take the average of thethree readings. Refer to thepotassium conversion tablebelow to determine the levelof potassium in the soil.

20

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

PROCEDURE

1. Obtain a Mehlich 2 extractof the soil sample byperforming the Mehlich 2Extraction procedure on page10.

2. Using the 1-mL eyedropper, add 3.0 mL of thesample extract prepared inStep 1 to a 25-ml cylinder.

3. Add deionized water to the21-mL mark on the cylinder.Firmly cap the cylinder with a#2 rubber stopper, and invertto mix.

4. Add one Potassium 2Reagent Powder Pillow and 3mL of Alkaline EDTASolution to the cylinder. Capthe cylinder and invert severaltimes to mix. Allow thesolution to stand for at least 3minutes.

Perform a Mehlich2 Extraction

Repeat Steps6–7 twice

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

21

POTASSIUM, EXCHANGEABLE IN SOIL

POTASSIUM CONVERSION TABLE

DipstickReading mg/L 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, 118 mL MDB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22687-37Potassium 2 Reagent Solution Pillows, 25/pkg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14322-98Potassium 3 Reagent Powder Pillows, 50 pkg. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14323-96

APPARATUSCylinder, Graduated, Polymethylpentene, 25 ml. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2172-40Dropper, Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14197-05Potassium Dipstick . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45700-00Stopper, Neoprene, Solid, #2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14808-02

22

Texture Estimation of Soil

Routine soil analysis usually includes an estimation of soiltexture. This method is used when exact proportions of sand,silt and clay are not needed or 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 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 added toform the categories on the right side of the triangle.

b. If sand is very prominent, the prefix sandy is added to formthe 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.

DIAGRAM FOR ESTIMATING SOIL TEXTURE

23

24

SECTION 5 IRRIGATION WATER ANALYSIS PROCEDURES

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

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

25


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.



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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14035-99Nitrogen Stock Solution, 15 mg/l, 118 ml MDB. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24151-37

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

NO3––N in Sample =

Average of 3 readings

26

pH in Irrigation WaterElectrode 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 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 instrumentby adjusting the calibration screw near the pocket clip with thetrim tool (screwdriver) provided to obtain a reading of 7.0.

PROCEDURE

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

2. Immerse the tip of thecalibrated Pocket Pal pHTester 1 inch below thesurface of the sample and stirgently.

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

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

27

pH IN IRRIGATION WATER

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

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/offswitch to off and cover theelectrode with the protectivecap before storing.

28

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

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.


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. Thisstep minimizes dilution of thesample with the rinse water.

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

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

PROCEDURE

29

PHOSPHORUS IN IRRIGATION WATER


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.



7. Take the average of thethree readings. Divide thisvalue by 10 to obtain themg/L PO4 in the sample. Toconvert 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 Disc, Phosphate, High Range, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24898-00Color Viewing Tube with caps, plastic, pk/4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46600-04

PO4 (mg/L) =

Average of 3 Readings___________________10

P = PO4 (mg/L)________3.1

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.

ORDERING AND TECHNICAL ASSISTANCE

Documents

NPK-1 SOIL KIT MANUAL - Hach Company