The method describes the procedure required for analysis of soil organic carbon

1. Estimation of soil organic carbon in
forest ecosystem
Sanu Raja Maharjan 2019

2. • Organic matter makes up just 2-10% of the
soils mass but has a critical role in the
physical, chemical and biological function of
soils.
• Organic matter contributes to nutrient
turnover and cation exchange capacity, soil
structure, moisture retention and availability,
degradation of pollutants, greenhouse gas
emissions and soil buffering.
Sanu Raja Maharjan 2019

3. • About 58% of the mass of organic matter
exists as carbon. So if we know the organic
matter content in a soil we can estimate the
amount of organic carbon.
• Organic matter (%) = total organic carbon (%)
x 1.72
• Carbon Levels are commonly highest in
surface soils but wide variations from almost
zero to above 15% C are possible. Presence of
Sanu Raja Maharjan 2019

4. • Soil organic matter also exists as four distinct
fractions which vary widely in their size,
composition and turnover times in the soil-
dissolved organic matter, particulate organic
matter, humus, resistant organic matter etc.
Sanu Raja Maharjan 2019

5. • Soil organic carbon (SOC) is the carbon (C)
stored in soil organic matter (SOM). Organic
carbon (OC) enters the soil through the
decomposition of plant and animal residues,
root exudates, living and dead
microorganisms, and soil biota. Soil Organic
Carbon (SOC) is the main source of energy for
soil microorganisms.
Sanu Raja Maharjan 2019

6. • SOC is one of the most important constituents
of the soil due to its capacity to affect plant
growth as both a source of energy and for
nutrient availability through mineralization.
Sanu Raja Maharjan 2019

7. Procedure
• Bulk density
• Bulk density is needed for the calculation of
soil organic carbon. Bulk density was
estimated through core sampler method . Soil
sample collected were oven dried at 105oC
until constant weight. Bulk density of soil was
calculated:
• Bulk density = wt. of oven dried soil/volume of
core sampler.
Sanu Raja Maharjan 2019

8. % of Organic carbon (SOC)
About 100 gm soil sample collected from each plot and stratum were
air dried in laboratory and sieved with 2 mm sieve. Finally the
percentage of OC was determined with the help of titrimetric
method given by (Walkley and Black, 1934).
For its determination following procedure were followed.
Air dried soil samples were passed through a 2 mm sieve to prepare
sample for determining soil organic carbon.
0.5 gm. of dried soil was weighed and transferred to the well
labeled oven dried 500 ml conical flask.
10 ml 1 N potassium dichromate solution and 20 ml conc. sulphuric
acid was added and mixed by gentle swirling.
The flask was kept for about 30 minutes to react with the mixture.
Sanu Raja Maharjan 2019

9. After the reaction was over, the mixture was diluted with
200 ml of distilled water and 10 ml of phosphoric acid
was added followed by 1 ml of diphenylamine
indicator.
The sample was titrated with 0.4 N ferrous ammonium
sulphate, until end point is marked with changed color
from black to the brilliant green.
The blank was run as followed by above procedure
without soil sample.
Sanu Raja Maharjan 2019

10. % Soil Organic Carbon is calculated as:
Where,
g=weight of sample in gram,
T=ml ferrous solution with sample titration
S=ml ferrous solution with blank titration.
Sanu Raja Maharjan 2019

11. Calculation of SOC
The carbon stock density of soil organic carbon was
calculated as given by equation(Pearson et al., 2007):
SOC = %C × ×d
Where,
SOC = Soil organic carbon stock per unit area (gm/cm2)
%C = Carbon Concentration
 = Soil bulk density (gm cm-3)
d = the total depth at which sample was taken (cm)
Sanu Raja Maharjan 2019