This presentation shows the presence and types of organic matter in the soil.

1. Organic Matter in Soil
By
Mr. Muhammad Ullah Afridi

2. Soil Organic Mater (SOM):
Soil organic matter is the
component of soil, consisting of plants and animals
residues at various stages of decomposition, cells and
tissues of soil organisms and substances synthesized
by soil organisms.
SOM exerts numerous +ve effects on soil physical and
chemical properties s well as the soils capacity to
provide to provide regulatory ecosystem services.
Particularly, the presence SOM is regarded as being
critical for soil function and soil quality.

3. The pie chart represents organic matter in soil before
cultivation. After land has been cultivated for one or two
decades, much of the active fraction is lost and stabilized
organic matter makes up more than half of the soil organic
matter.

4. SOM
Soil Organic matter
encompasses
all organic components
of a soil:
Fresh residues
Decomposing
organic
matter
Stable organic
matter
Living organisms

5. Soil Organic Matter
Soil organic matter
all living organisms
(microorganisms,
earthworms, etc),
fresh residues (old plant
roots, crop residues, recently
added manures),
well-decomposed residues
(humus).
The SOM content of agricultural
topsoil is usually in the range of 1
to 6%.
This amount is the result of all
additions and losses of SOM that
have occurred over the years.
Non-cultivated soils will have
SOM ranges between 3-10%
Citizen Science – Kansas State

6. Fresh Residues
Up to 15% of organic matter is
fresh residue (usually <10)
Comprised mainly of
litter fall
Many of the different types of
plant litter can be recognized.

7. Decomposing Organic Matter
Plant material is transformed
from one organic compound
to another mainly by
organisms in the soil
Organisms create by-products,
wastes, and cell tissue
Compounds released as waste
by one organisms can often
be used as food by another

8. Soil Organic Matter (SOM)
SOM is labile* -it can
decline rapidly if the soil
environment changes and
renewable
-it can be replenished by
inputs of organic material
to the soil.
* Labile = Constantly or readily
undergoing chemical, physical, or biological change
or breakdown; unstable.

9. Adequate levels of SOM can be maintained with:
1. proper
fertilization,
2. crop
rotations, and
tillage
practices
3. Returning
crop residues
to the soil.

10. Factors Controlling SOM
1) Kind of parent materials (texture
primarily), climate, slope, and
management practices that exist.
(Sandy = Low & Clay = High)
2) Climate: PMs that have not lost their
nutrients from excessive rainfall
(leaching), and areas where
temperature and water are adequate
will have high SOM.
3) Management practices that affect
crop biomass (yield and straw)
production (water, fertilizer, variety),
residue maintenance (equipment,
harvest), and litter (wind) will also
affect SOM content.
4) As dry matter production increases,
SOM increases.
5) However, only that which remains
after harvest along with root biomass
will influence long-term SOM content.
Established in 1876 the Morrow Plots are the oldest agronomic experiment fields
in the United States. They include the longest-term continuous corn plot in the
world. Located near the center of the University of Illinois' Urbana campus.
manure, lime and phosphorus (MLP)
Morrow Plots – Why the difference in SOM?

11. Active Fraction
10 to 30% of the soil
organic matter (active
fraction) is responsible
for maintaining soil
microorganisms.
The active fraction of
organic matter is most
susceptible to soil
management practices.
(Inactive = humus)
ACTIVE

12. Adding Fresh OM
In a soil which at
first has no readily
decomposable
materials, adding
fresh tissue under
favorable
conditions:
1) immediately
starts rapid
multiplication of
bacteria, fungi,
and actinomycetes,
2) which are soon
actively
decomposing the
fresh tissue.
ADDED

13. Fresh SOM
as most readily
available energy
sources are used up,
microorganisms again
become relatively
inactive,
leaving behind a dark
mixture usually
referred to as humus
– a stable organic
compound

14. Stable Organic Matter -Humus
Thus, soil organic
compounds become
stabilized and resistant to
further changes by
microorganisms
Stabilized organic matter
acts like a sponge and can
absorb six times its
weight in water

15. HUMUS
Newly-formed humus=
a) combination of
resistant materials from
the original plant tissue,
b) compounds synthesized
as part of the
microorganisms' tissue
which remain as the
organisms die. (Fulvic and
Humic Acid)
humus is mostly resistant
to further microbial
attack- N and P are
protected from ready
solubility
Leaf Humus

16. Function of Humus
holds water and nutrients;
sticks together & helps
establish and maintain a
strong crumb structure &
thus reduce soil erosion
provides some nutrients
(N & P) as it is slowly
decayed by microbial
activity,
Buffers effects of
pesticides
humus decomposes at the
rate of 2.5% per year
Creates good soil “ Tilth”
Coates the sand, silt, clay
particles making them
dark and the darker the
color, the greater the
amount of soil humus
present.
Humus = High Medium Low

17. Soil Quality
Soil quality is the capacity of soils
within landscapes to sustain biological
productivity, maintain environmental
quality, and promote plant and animal
health.
Protecting soil quality like protecting
air quality and water quality should be
fundamental goal of our Nation’s
Environmental Policy.
http://www.directs
eed.org/soil_qualit
y.htm
http://www.nrsl.umd.edu/research/NRSLResearchAreaInfo.cfm?ID=14
Poor Good