Determination of organic matter and organic carbon from soil

Organic carbon in organic matter is oxidized by known but excess of chromic acid. The excess chromic acid not reduced by organic matter is determined by back titration with standard ferrous sulphate solution, using diphenylamine or ferroin indicator. The organic carbon content in soil is calculated from the chromic acid utilized (reduced) by it.

1. Determination of soil
organic matter

2. Principle :
Organiccarboninorganicmatterisoxidizedbyknownbut
excessofchromicacid.Theexcesschromicacidnotreduced
byorganicmatterisdeterminedbybacktitrationwithstandard
ferroussulphatesolution,usingdiphenylamineorferroin
indicator.Theorganiccarboncontentinsoiliscalculatedfrom
thechromicacidutilized(reduced)byit.

3. The organic carbon content of soil is estimated by
using the following methods:

4. Reagents:
EquipmentandApparatus :

5. Procedure

6. Calculations:
(X-Y) ml X 0.003 X100
(X-Y) X N X 0.003 X100
Weight of soil (W)
58
=
Organic matter (%) in soil=Organic carbon (%) in soil X 100/58
OM (%)= OC (%) X 1.724
1.724 : Van Bemmelenfactor

7. Soil Rating Organic Carbon (%)
1. Very low Less than 0.20
2.Low 0.21 to 0.40
3. Moderate 0.41 to 0.60
4. Moderately high0.61 to 0.80
5. High 0.81 to 1.00
6. Very high Greaterthan 1.00
Interpretation of results: