Nitrogen in the soil - Determination.

TITLE  - Determination of available nitrogen in the soil.

METHOD - Alkaline permagnate.

Scientists : Subbiah and asijo 1956.

Principle - the organic matter in the soil is oxidized by Kmno4 in presence of NaoH. The ammonia released during oxidation is absorbed in boric acid to convert the ammonia to ammonia borate.

The ammonia borate formed is titrated with standard H2So4 from the volume of standard H2So4 required for reaction with ammonium borate.The Nitrogen is calculated.

 REAGENTS  - 

1) Potassium  permagnate Kmno4 (0.32%).-

Dissolve 3.2 gram potassium permagnet in one litre of distilled water with the intermittent shaking till it completely dissolved. store in umbrella colour bottle and keep it in the dark. 

2)Sodium hydroxide solution NaoH (2.5%)-

Dissolve 25gm of pure sodium hydroxide in 1 litre of distilled water.

3) Boric acid H3Bo3 (2%) 

Dissolve 20 gram of boric acid AR grade in 800ml distil water by heating to content cool it and diluted to 1000ml volume.

 4) Mixed indicator :bromocresol green + methyl red. -

Weight out separately 99 gm bromoresol green and 60mg of well powder methyl red and dissolved them together in 100 ml ethyl alcohol.

5) working Boris acid solution -

Add 20 ml of mixed indicator to 1 litre of 2% boric acid solution and adjust the pH to 5.0 after shaking or add 0.1 normality NaoH continuously until the solution assumes reddish purple tinge wine red colour.

6) standard sulphuric acid : H2so4    (0.02 N) -

Standardized the H2so4 solution using standard NaoH. NaoH be standardized against 0.02 normality H2So4 standard oxalic acid or 0.02 normality of potassium hydrogen phthalate

PROCEDURE:

1)Take 20 gram of soil sample in round bottom flask.

2) 20 ml distilled water plus paraffin liquid and glass beads.

3) Add 100ml potassium permanganate and hundred ml NaoH. 

4) Distilled And collect distillate in a beaker containing 20 ml working boric acid solution.

5) Collect approximately 100 ml distillate.

6) Titrate the distillate in beaker containing 20 ml working boric acid solution.

7)Collect approximately 100 ml distillate.

8) Titrate the distillate with 0.02 normality sulphuric acid till colour changes from Green to red.

9) Record the burette reading.

10) Run the blank sample.

   OBSERVATION - 

1) weight of soil sample taken - - - gram.

2) Volume of standard H2 S o4 required for soil sample - - - - ml.

3) volume of standard H2 S o4 required for blank sample - - - - ml.

4) Normality of H2 s o4 -   0.002 N.

FORMULA  -

Available nitrogen (kilogram per hectare = (A-B) × normality of H2 s o4 × 0.014 × 

weight of 1 hectare soil ÷ weight of soil sample.

Where  A = soil sample reading.

        B = blank sample reading.

Weight of 1 hectare soil = 2240000 kilogram.

Weight of soil sample = 20 gram.

CALCULATION  -

Available nitrogen = (A-B) × 0.02 × 0.0 14 × 2240000/20

Available nitrogen =(A-B) × 31.36

Available nitrogen = ------- kilogram per hectare.

INTERPRETATION  - (SIX TIER SYSTEM) 

Ratings             :         Available nitrogen                                                       kilogram per hectare.

1) very low.             -           <140

2) low.                      -          141-280

3) medium.             -            281-420

4)moderately.         -            420 -560

5) high.                    -             561 -700

6) very low.              -             >700.

RESULTS - 

Hence given soil sample is -------(rating) in available nitrogen content.