This Slide is Prepared by Abdullah Al Noman Neion with the help of his fellow groupmates. - Faculty of Agriculture Batch 57 Bangladesh Agricultural University

1. DETERMINATION OF TOTAL NITROGEN
IN SOIL BY SEMI-MICRO KJELDAHL
METHOD
- Abdullah Al Noman Neion
Department of Soil Science , Bangladesh Agricultural University

2. Importance of Nitrogen in Soil
Essential for plant
growth and
development
Component of
chlorophyll and
organic matter
Regulates soil pH
levels
Vital for soil
microbe growth
Limits plant
growth if
deficient
Commonly used
in agriculture
Involves complex
nitrogen cycling
Improves soil
health and
sustainable
agriculture

3. Objectives of Determining
Total Nitrogen in Soil
• Assess soil fertility
• Determine nitrogen requirements
• Monitor soil nitrogen changes
• Evaluate environmental impact
• Understand nitrogen cycling
• Support sustainable agriculture
• Guide fertilizer and soil management
• Monitor soil conservation efforts

4. Sources of
Nitrogen in
Soil
Atmospheric deposition
Nitrogen-fixing plants and bacteria
Decomposition of organic matter
Commercial fertilizers
Manure and compost
Nitrification of ammonium compounds
Fixation of nitrogen gas in soil
Application of sewage sludge
Release from plant roots and root exudates

5. Functions of
Nitrogen in Plants

6. Symptoms of
Nitrogen Deficiency
• Very slow growth and look weak and
stunted.
• Older leaves have a light green
or yellow colour.
• As nitrogen is mobile in the plant
and moves to where it is needed,
these older and lower leaves are
always first to show symptoms of
deficiency.

7. Leaching Loss
• The nitrate-nitrogen is lost in
drainage or with percolating
water.
• The amount of nitrogen lost
depends upon the climate and
cultural conditions.
• In humid region or a water- logged
condition, losses of nitrate by
leaching are significant.
• In arid and semi-arid regions, such
losses are minimum

8. Volatilization
• The loss of nitrogen to the atmosphere as ammonia gas.
• The greatest losses occur from surface application of fertilizer
containing ammonium (urea or blended dry fertilizers), particularly on
a high pH soil and/or high temperature during hot, windy weather, or
on dense crop residue which inhibits fertilizer-soil contact.

9. Denitrification
• Denitrification occurs when oxygen levels
are low, anaerobic microorganisms strip
oxygen from nitrate which produces
nitrogen gas, nitric oxide or nitrous oxide.
• When this occurs, these gases may
diffuse out of the soil into the air.
• The following four conditions that
contribute to denitrification are: Wet or
poorly drained soil; compaction; warm
soil temperatures; or readily
decomposable organic matter.

10. Methodology
Two methods have gained general
acceptance for determination of
total Nitrogen:
1. The Kjeldahl method
2. The Dumas method

11. Kjeldahl Method
It is a method for the quantitative determination of nitrogen contained
in organic substances, the nitrogen contained in the inorganic
compounds ammonia and ammonium.

12. Dumas Method
This method is based upon the fact that nitrogenous compound when
heated with cupric oxide in an atmosphere of CO2 yields free nitrogen.

13. Reagents Required
CONC. H2SO4 NaOH 35% H3BO3 INDICATOR
SOLUTION
CATALYST
MIXTURE

14. Functions of
Reagents
Digestion
Distillation
Indicator
Raises temperature and oxidation

15. Principle
Major steps:
• Digestion: Organic N converted to NH4
+
• Distillation: NH4
+ converted to NH3 and trapped
by indicator
• Titration: Trapped NH3 determined

16. Digestion:
Organic N is converted to NH4
+ by digestion with conc. H2SO4 in
presence of substances (catalyst mixture) that promote this conversion.
Catalyst mixture:
K₂SO4, CuSO4.5H₂O and Se in the ratio of 100:10:1 or 10:1:0.1

17. Distillation:
The NH4
+-N in the digest is converted to NH3 by distillation with
strong alkali (35% NaOH) and this is trapped with H3BO3 indicator
solution.

18. Titration
The NH3 trapped in H3BO3 is determined by titration with 0.01N H2SO4.
NH3H3BO3+H2SO4 (NH4)2SO4+H3BO3
Green Pink

19. Procedure
01
Take 1 g soil
sample
02
03
04
1.1 g of K2SO4
catalyst
mixture
5 ml H2SO4
(conc.)
Heat up to
360°C
(colorless)
Allow to cool
& add 20 ml
H2O, then
Swirl the flask

20. Procedure (contd.)
05
Vol. up to 100
ml with DW &
Transfer 25 ml
in test tube
06
07
08
Add 20 ml of
H3BO3
indicator &
place into
distillation unit
Steam supply
for 4 minutes
(pumping
NaOH)
Volatilized
NH3 trapped
with H3BO3 &
Titration with
0.01 N H2SO4

21. Calculation
1L 1N H2SO4 ≡ 14g N
Or, 1000mL 1N H2SO4 ≡14g N
Or, 1mL 1N H2SO4 ≡ 0.014g N
Or, 1mL 0.01N H2SO4 ≡ 0.00014g N
% N = {(Vol. of 0.01N H2SO4 required in titration – Blank)*100} ÷
Weight of soil taken
=0.0078

22. Result
The percentage Nitrogen of
the supplied soil sample was
0.0078

23. Please
Conserve Soil :)