Potassium in solution is atomized to flame and the flame excites atom of potassium causing them to emit radiation at specific wavelength. The amount of radiation emitted is directly proportional to concentration of the solution and it is measured in a flame photometer with suitable filter, which transmits only potassium wavelength (768 nm red filter).

2. Functions of potassium in plants
 Increases root growth and improves drought resistance
 Activates many enzyme systems
 Maintains turgor; reduces water loss and wilting
 Aids in photosynthesis and food formation
 Reduces respiration, preventing energy losses
 Enhances translocation of sugars and starch
 Produces grain rich in starch
 Increases protein content of plants
 Builds cellulose and reduces lodging
 Helps retard crop diseases

3. Principle
Potassium in solution is atomized to flame and the flame excites atom
of potassium causing them to emit radiation at specific wavelength.
The amount of radiation emitted is directly proportional to
concentration of the solution and it is measured in a flame photometer
with suitable filter, which transmits only potassium wavelength (768
nm red filter).

4. Tri-acid extracts preparation:
 The tri-acid extract of plant material is prepared for the estimation of
total K.
 A known weight of the plant sample is digested with triple acid to
destroy the organic fractions and to bring the mineral constituents into
solution.
Reagents Required:
 Triple acid mixture – 9:2:1 ratio of conc. nitric acid, conc. sulphuric
acid and perchloric acid.

5. Procedure
Weigh about 1 g of the given plant sample into a 100 ml conical flask.
Add 15 ml of the triple acid mixture and cover the mouth of the flask with
funnel and
Digest the contents over a sand bath till a clear colourless solution is
obtained.
Dilute with distilled water and transfer to a 100 ml volumetric flask.
Wash the conical flask with small increments of water and add the washings
to the volumetric flask.
Make up the volume to 100 ml with distilled water and reserve it for
further analysis.

6.  Preparation of std. K solution: Make a stock solution of 1000 ppm K by dissolving
1.908 g of AR grade potassium chloride (dried at 600C for 1 hr) in distilled water
and diluting to 1 L.
 Transfer 10 ml of 1000 ppm K solution into 100 ml standard flask and make up
the volume. That gives 100 ppm of potassium. From that, prepare solutions
containing 10, 20, 30, .. 90 ppm potassium by pipetting out 10, 20, 30,… 90 ml of
100-ppm solution and make up the volume to 100 ml.
 The flame photometer is calibrated by feeding the standards.
 Introduce the tri-acid extract in the flame photometer and get concentration of
potassium and expressed in per cent.

7. Flame photometer

8. Calculation:
 Weight of the sample taken = W g
 Volume of tri-acid extract prepared = 100 ml
 Flame photometer reading = T
 Concentration of K in the standard curve for recorded T= X ppm
 Concentration of K in per cent = X / 106 x 100/w x 100
Result:
 Total potassium content in given plant material is _____%