Principle

Soil organic carbon is oxidized by potassium dichromate (K₂Cr₂O₇) in the presence of concentrated sulphuric acid (H₂SO₄).The excess (unreacted) dichromate is titrated against ferrous ammonium sulphate (FAS) using diphenylamine indicator.The amount of dichromate reduced is proportional to the organic carbon present in the soil.

Requirements

Chemicals :

  1. 1 N Potassium dichromate (K₂Cr₂O₇)
  2. Concentrated sulphuric acid (H₂SO₄)
  3. 0.5 N Ferrous ammonium
  4. sulphate(FAS)Diphenylamine indicator
  5. Distilled water

Preparation of Solutions

1) Preparation of 1 N Potassium Dichromate (K₂Cr₂O₇)

Equivalent weight of K₂Cr₂O₇ = 49 gFor 1 N, 1 litre

2) Preparation of 0.5 N Ferrous Ammonium Sulphate (FAS)

Equivalent weight of FAS = 392 g For 500 ml: 98 gm

Apparatus

  1. Burette
  2. Pipette (10 ml)
  3. Conical flask (500 ml)
  4. Electronic balance
  5. Sieve (0.5 mm)

Procedure

  1. Take 1 g of air-dried, sieved soil in a 500 ml conical flask.
  2. Add 10 ml of 1 N K₂Cr₂O₇ solution.
  3. Add 20 ml concentrated H₂SO₄ carefully and swirl gently.
  4. Allow the mixture to stand for 30 minutes.Add 200 ml distilled water.
  5. Add 2–3 drops of diphenylamine indicator.
  6. Titrate with 0.5 N FAS until the colour changes from violet to green.
  7. (Ferroin indicator colour change: blue-green → wine red / reddish brown)
  8. Run a blank titration without soil.

Calculation :

Organic Carbon = (B-S)× N×0.003×1.33×100/Wt.Of Soil

Where,

B = Volume of FAS used in blank (ml)

S = Volume of FAS used in sample (ml)

N = Normality of FAS 0.5 N

  1. 0.003 = Carbon equivalent (gm)
  2. 1.33 = Correction Factor
  3. Blank Reading (B) = 26.1ml
  4. Sample Reading = 23.8 ml
  5. Weight Of Soil = 1 gm

Organic Carbon = (B-S)× N×0.003×1.33×100/Wt.Of Soil

= (26.1- 23.8)×0.5×0.003×1.33×100/1

=2.3×0.5×0.003×1.33×100/1

=1.15×0.003×1.33×100/1

=0.00345×1.33×100/1

=0.0045885×100/1

=0.458/1

=0.458%

Conclusion (Organic Carbon)

The given soil sample contains 0.458% organic carbon. Since this value is below 0.5%, the soil is classified as having low organic carbon content.

Low organic carbon indicates reduced soil fertility, lower microbial activity, poor soil structure, and limited availability of nutrients to plants. Such soil may also have a lower water-holding capacity.

Therefore, to improve soil health and fertility, the application of farmyard manure, compost, vermicompost, green manuring, and incorporation of crop residues is recommended. These practices will help increase the organic carbon content and improve sustainable crop productivity.

Based on the laboratory analysis, the organic carbon status of the soil can be concluded as follows:

  1. Low organic carbon (< 0.5%) indicates poor soil fertility, low microbial activity, and reduced nutrient availability. Such soils require the addition of organic manures, compost, crop residues, or green manuring.
  2. Medium organic carbon (0.5–0.75%) reflects moderate soil fertility and satisfactory physical and biological properties.
  3. High organic carbon (> 0.75%) signifies good soil health with better nutrient supply, improved soil structure, and higher productivity.

    Sr No Farmer Name
    1. Tanaji Nanasa Dhumal
    2 Nikhil Eknath Chore
    3 Subhash Dnynoba Dhumal
    4 Ashok Bappu Novote
    5 Ramdas Kisan Yelbhar
    6 Mahesh Pandurang Gawade
    7 Bhau Asaram Gade
    8 Devram Babu Shelke
    9 Anil Baburao Godse
    10 Prabhakar Vaman Mohite
    11 Ramesh Shankar Daphal
    12 Sangita Vilas Punde
    13 Balasaheb Sitaram Vidhate
    14 Swapnil Rajendra Shinalkar
    15
    Kisan Anandrav Parhad
    16
    Madhukar Baburav Dhumal
    17
    Abhijit Kulkarni
    18
    Vilas Jayshing Dhumal
    19
    Baburao Kisan Chore
    20
    Subhash Namdev Dhumal
    21
    Pandurang Prabhakar Jadhav
    22
    Shahuraj Vithal Thite
    23
    Sampat Kantilal Dhumal
    24
    Kailas Vishnu Khaire
    25
    Pappu Tukaram Kardile
    26
    Dushant Sukhdev Parhad
    27
    Amol Alkabai Jinturkar
    28
    Anil Jayashing Yewale
    29
    Pradip Sahebrao Jadhav
    30
    Chandrabhaga Ganpat Shelke
    31
    Avinash Laxman Daphal
    32
    Phulabai Pandit Bhosale
    33
    Ganesh Narayan Dhumal
    34
    Santosh Sudam Madake
    35
    Somnath Sayaji Kudekar
    36
    Popat Shakar Gaiwad
    37
    Dnyneshower Jonku Midgule
    38
    Gurudev Shankar Rajgurav
    39
    Pandurang Dashrat Bhujbal
    40
    Dattatroy Nanabou Bavale
    41
    Jainuddin Kamubhai Mulani
    42
    Baburav Gajaba Khaire
    43
    Rajendra Vithal Dhumal
    44
    Rohini Pralhad Khaire
    45
    Sambhaji Shankar Dhumal
    46
    Kaluram Baban Sakore
    47
    Ramdas Balaji Thorat
    48
    Amrut Kaluram Mohite
    49
    Eknath Sadashiv Khaire
    50
    Gorak Kondiba Bhor