Determination of available phosphorus in soil

 TITLE  - Determination of available Phosphorus in soil. 

Method - 

Acid soil - Bray's method. 

Alkaline soil - olsen method.

 Regents.-

1) 0.5 ml NaHco3 (PH = 8.5 ) -

Dissolved 21 gram sodium bicarbonate in 450 ml water adjust the pH 8.5 and make up the volume up to 500 ml .

2) Activated charcoal 

3) solution 'A' -

a) Dissolved 12 gram ammonium molybdate in 250 - 300 ml distilled water .

b ) Dissolved 0.291 gram antimony potassium tartrate in 100 ml distilled water.

 c) 5 normality - H2 s o4 

Dissolved 140 ML concentrated H2 S o4 in 1000 ml water .

Solution 'A'-

Add cool ammonium molybate in normal H2 s o4 solution followed by cool antimony potassium tartrate and volume is made up upto 2 litre .

Solution 'B'-

• Dissolve 1.056 gram ascorbic acid in 200 ml of solution 'A'. solution B should be prepared fresh.

•  0.25% - 2.4 paranitrophenol. - 

Dissolved 0.25 gram 2.4 para-nitrophenol in hundred gram distilled water .

• 5 normality H2 s o4 -

Dissolved 14 ml cost concentrated H2 s o4 in 100 ml distilled water .

Procedure  -

• Extraction  -

Take 2.5 gram soil in 250 ml conical flask  add one teaspoon activated charcoal and 50 ml 0.5 molar sodium bicarbonate.

 Shake for half hour and on mechanical Shaker filter the content to whatsman filter paper number 1 and collect the filtrate .

• Estimation -

prepaid out 5 ml Sodium Bicarbonate extract filtrate into 25 ml volumetric flask.

  Add 2 to 4 drops para-nitrophenol (yellow).

 Add 5 normal of H2so4 still colour changes from yellow to colourless .

Makeup Volume 20 ml with distilled water.

 Add 4 ml of solution 'B' make up the final volume (25 ml ) 

keep this for half hour for colour development (blue colour )

After 30 minute take measured observance on spectrophotometer at 882 NM wavelength.

 Run the blank .

Preparation of standard curve. 

1) Standard  P solution (stock solution )-

  Take 0.439 gram potassium dihydrogen phosphate in 500 Ml distilled water. 

                              +

2) 25ml *N H2so4 & volume made up to 1 litre this is 100 PPM stock solution of potassium.

 WORKING  P SOLUTIONS 

Take 10 mil stock solution in in 500ml volumetric flask and make up the volume in the distilled water .

Preparation of standard curve. -

Prepared the series of standard by taking 0, 1,  2, 3, 4, 5 ,&10 ml working solution in 25 ml volumetric flask.

 Add 5 normality of sodium bicarbonate solution followed the procedure same as estimation. 

Graph factor-

X axis conc.                      Y axis

 In ppm.                              obserbance  at.                                                882 NM  

0.00.                      -

0.08.                      -

0.16.                      -

0.24.                      -

0.32.                      -

0.40.                      -

0.48.                      -

0.56.                      -

0.64.                      -

0.72.                      -

0.82.                      -

Draw graph factor on graph paper.

Calculations -

Formula -

Available phosphorus kg/hq = 

R × spectrophotometer reading × final volume 

× total volume of extract/volume of     filtrate  taken

× 1/weight of soil 

×2.24×10 rest 6/10 rest 6

Where R is graph factor. 

P = Graph factor × spectrophotometer reading 

× 25ml 

× 50÷5

× 1÷2.5

× 2.24 × 10 rest to 6÷10 rest to 6.

P = Graph factor 

× spectrophotometer reading ×25ml × 10 × 0.4 ×2.24

P =  Graph factor × spectrophotometer reading × 224

P = -----kg/hq

SIX TIER SYSTEM  -

very low.                   <7 kg/hq

Low.                           7.1 to 14 kg/hq

Medium.                   14.1 to 21 kg/hq

Moderately high.      21.1 to 28 kg/hq

High.                          28.1 to 35 kg/hq

Very high.                  >35 kg/hq

Results 

According  to six tier, 

P containt in given soil is -------(ratings)