- Soil organic matter (SOM) encompasses all organic components in soil, including living organisms, fresh residues, and well-decomposed residues known as humus. SOM content in agricultural soils is typically 1-6% and provides numerous benefits to soil health. - Fresh residues and decomposing organic matter are broken down by soil organisms, transforming plants materials into stable humus. Humus acts like a sponge, holding water and nutrients, and helps maintain good soil structure. - Maintaining adequate levels of SOM through practices like proper fertilization, crop rotations, and returning crop residues can improve soil quality by

2. Soil Organic Matter
A Lecture By
Mr .Allah Dad Khan

3. Soil Organic Matter=SOM
Is this a healthy soil? Is this a healthy field?

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. How is SOM
Measured?
SOM is usually measured in the
laboratory as organic carbon,
Soil organic matter is estimated
to contain 50% organic carbon
(varies from 40 to 70%) with
the rest of the SOM
comprising of other elements
(eg, 5% N, 0.5% P and 0.5% S).
A conversion to SOM from a
given organic carbon analysis
requires that the organic
carbon content be multiplied
by a factor of
2.00(1.00/0.50).
Thus, 2% SOM is about 1 %
organic carbon.
Testing for Soil Organic Carbon
UF/IFAS Extension Soil Testing Laboratory

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. SOM Maintains soil “Tilth”
 aiding
infiltration of
air and water
 promoting
water
retention
 reducing
erosion
BMI

19. SOM = SOIL
HEALTH
 Measuring SOM is one step in
assessing overall soil quality
or soil health -
 measuring various key
attributes of soil organic
matter quantity and quality
will give an indication of the
health of the soil.
 Or Look at the state of the
soil organisms in the soil.
 Or look at how well the soil
“Holds Together”.
“If your soil clods can't pass the water
test, change your management practices.
It will help your bottom line as well as the
soil.” – Ray Weil – Univ of Maryland
Simple clod test: Healthy soil, at
left, holds together in water, while
poor soil falls apart.

20. Use of Soil Quality
 1) Match use and management
of land to soil capability,
because improper use of a soil
can damage it and the
ecosystem.
 2) Establish a baseline
understanding about soil
quality so that we can
recognize changes as they
develop.
 3) Use baselines to determine
if soil quality is deteriorating,
stable, or improving.
 Thus soil quality becomes a
good indicator of the health of
an ecosystem.
NatureWatch

21. 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

22. SOIL HEALTH
 Soil Health is the change
in Soil Quality over time
due to human use and
management or to natural
events.
 Descriptive terms for Soil
Health
 Organic Matter - high
 Crop appearance =
green, healthy,lush
 erosion – Soil will not
erode
 earthworms – numerous
 infiltration – fast, no
ponding
 Compaction - minimal
Cornell researcher George Abawi describes soil health
strategies at an Onion Council field day in Wayne County,
N.Y.Photo by Carol R. MacNeil.
In Vernon and surrounding counties are the largest
concentration of organic farmers in Wisconsin.

23. Is this a good Idea? DYAD
 The Grimm Brother's fairy tale, Rumpelstiltskin spins straw
into gold.
 Thanks to advances in biotechnology, researchers can now
transform straw, and other plant wastes, into "green" gold -
cellulosic ethanol.
 While chemically identical to ethanol produced from corn or
soybeans, cellulose ethanol exhibits a net energy content
three times higher than corn ethanol and emits a low net
level of greenhouse gases.
 Recent technological developments are not only improving
yields but also driving down production cost, bringing us
nearer to the day when cellulosic ethanol could replace
expensive, imported "black gold" with a sustainable,
domestically produced biofuel.
 IS THIS A GOOD THING TO DO?
http://www.harvestcleanenergy.org/enews/enews_0505/enews_050
5_Cellulosic_Ethanol.htm


24. What is the health of this soil?