analysis of potassium in soil and fertilizers

7/29/2019 Analysis of Potassium in Soil and Fertilizers

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Soil Analysis for Ammonium Acetate Extractable

Potassium

Hafeez ur RehmanAgricultural Officer

Soil and Water Testing Laboratory, Gujranwala


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Principle Ammonium Acetate Solution is used to extract

Potassium from exchange sites of soil colloids.

Ammonium ions of the solution are replacePotassium ions from exchange sites.

As a result, the released K in the soil solution can bedetected by flame photometer


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Principle of flame photometryFlame photometry relies upon the fact that:

The compounds of the alkali and alkaline earth metals canbe thermally dissociated in a flame and

The atoms produced will be further excited to a higherenergy level.

When these atoms return to the ground state they emitradiation which lies mainly in the visible region of thespectrum. Each element will emit radiation at a

wavelength specific for that element. The measurement of the emitted radiation forms the basis

of flame photometry.


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Equipment/Apparatus Required

Weighing balance

Mechanical shakerFlame Photometer

Cylinder, 50 mlVolumetric flasks,100 mlPipette, 5 and 10 mlConical flasks 250 ml

Wash bottle


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Reagent/Medias Required

A. 1N NH4OAC:Dissolve 77.1 g ammonium acetate

(CH3COONH4) in 800 ml distilled water and make the

volume upto 1 litre mark.Adjust pH 7.0 using either NH4OH or HClB. Stock Solution:

Dissolve 1.9103 g oven dried KCl in distilled water

and make volume upto 1 litre mark.This solution contains 1000 ppm KorCRM of 1000 ppm for Potassium


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MethodPreparation of working standard solution

Stock solution so prepared will be used for the preparationof working standard solutions by using formulaC1V1 = C2V2

WhereC1 = Concentration of stock solution in ppm

V1 = Volume to be taken of stock solution in mlC2 = Concentration of K to be required in ppm

V2 = Total volume to be required in ml

Working Standard Solution can be prepared of 0, 5,10, 15 and 20 ppm concentration


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Weigh 2.5 g air dried, ground, passed through 2 mmsieve soil sample into a 250 ml conical flask

Add 50 ml extracting reagent

Shake on a shaker for 30 minutes

Filter the extract

Determine K by flame photometer in ppm usinggraph readings


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CalculationsExtractable K (ppm) = reading (ppm) x 50/2.5 (DF)


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Interpretation of Soil Analysis for Potassium

Example:-Soil containing 60 ppm K then amount of K in kg acre-1

As we know,ppm= mg/kg

1 kg soil contains K = 60 mg2x106 kg soil (1 hectare) contains K = 60 x 2x106 mg2x106 /2.47 soil (1 acre) contains K = 60 x 2x106/2.47mg

2 x 106 x 602x106 /2.47 soil (1 acre) contains K = ______________ kg

2.47x1000x10001 acre soil upto 6 inch depth contains K = 0.81 x 60 kg/acre1 acre soil upto 6 inch depth contains K = 48.6 kg1 acre soil upto 6 inch depth contains K2O = 48.6 x 1.2046 kg1 acre soil upto 6 inch depth contains K2O = 58.32 kg/ acre


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Fertilizer Analysis for PotassiumHafeez ur RehmanAgricultural OfficerSoil and Water Testing Laboratory, Gujranwala

(Method No. 971.01 AOAC. Official Methods of Analysis, 1990)


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Equipment/Apparatus Required

Flame PhotometerElectronic balance

Volumetric flask 100 mlPipettes 1, 5, 10, 25, 50 ml

Wash bottleWeighing balance


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Reagent/Medias RequiredStock Solution:Dissolve 1.9103 g oven dried KCl in distilled water

and make volume upto 1 litre.

This solution contains 1000 ppm KorCRM of 1000 ppm for Potassium


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Method Working Standard Solution can be prepared of 0, 10,

20, 30, 40, 50 and 60 ppm concentration from stocksolution

Dissolve 1.0 g ground potassic fertilizer material in 100ml distilled water

Shake well to dissolve Filter the solution

Take 1ml from filtrate into another 100 ml volumetricflask and make volume with distilled water

Take readings on flame photometer using standardcurve procedure


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Calculations

K (ppm) x 10,000 (D.F) x 1.2046

%K2O = ___________________________10,000

So,

% K2O = K (ppm) x 0.12046


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Cautions/Safety Requirement

Always

Run a blank for accurate results

Run a standard sample of fertilizer for comparison


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Interpretation of Water Analysis for Potassium

Example:-

Irrigation water (suppoed 1 ppm K) upto 3 inch depth then theamount of K (kg acre-1) ?

Irrigation of 1 acre upto 3 inches depth contains water = 3 inch____x 43560 ft2 x 28.312

Irrigation of 1 acre upto 3 inches depth contains water = 308187 L1 L water contains K = 1 mg308187 L water contains K = 1 x 308187 mg

= _308187

1000x1000= 0.31 kg K

1 acre irrigation upto 3 inch depth contains K2O = 0.31 x 1.2046= 0.37 kg K2O/ acre


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Interpretation of Plant Potassium

Contents


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Example:-

To get 60 Monds yield of paddy, the uptake of Potassium (kg) ?

60 monds paddy yield = 60 x 40

= 2400 kgPaddy contains moisture = 20 %

so,

The moisture weight = 2400 x 20/100

= 480 kg

Remaining dry weight of paddy yield =2400-480

=1920 kg dry weight

100 kg paddy yield contains K = 1 kg KSo,

1 x 1920

1920 kg dry weight (60 monds) paddy contains K =________

100

= 19.2 kg K

60 monds paddy yield contains K2O = 19.2 X 1.2046

= 23.04 kg K2O

On dry weight basis the ratio

Straw: Grains

1 : 1

So, the quantity of K2O = 23.04 X 2

= 46.08 kg K2O


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THANKS

analysis of potassium in soil and fertilizers

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