Soil Carbon Slides

1
Basic Biological Factors ofSoil Carbon and Soil
Organic Matter
Teaching Team of the Agricultural Microbiology
Program, Faculty of Agriculture, Gadjah Mada
University
2
Photosynthesis
3
The Soil Food Web
4
The Soil Food Web

• Burrowing animals, insects, and earthworms mix,
  help form aggregates, and add nutrients to the
  soil. When animals die, they decompose returning
  nutrients to the soil. Insects chop up plant and
  animal residue which increases the surface area
  available to microorganisms for decomposition.
• Soil organisms are responsible for the
  transformation of plant material to humus. Plant
  and animal residue make up a large portion of
  organic matter (OM) in soil. SOM or humus is the
  glue that helps hold soil into aggregates. Plant
  cover helps stop both wind and water erosion as
  does the aggregation effect of SOM.

5
Carbon Cycle
6
Carbon Cycle

• CO2, through photosynthesis, is converted to
  plant material.
• When the crop is harvested and removed from the
  farm, carbon is lost. If livestock consume the
  crop, the carbon may be returned to the soil in
  the form of manure.
• Crop residue, roots, and manure are a carbon
  (energy) source for microorganisms.
• Converting organic carbon to CO2 is
  mineralization of carbon. When microorganisms
  respire, CO2 is released to the atmosphere.

7
Carbon Cycle

• Short-term SOM is residue that is readily
  decomposed. Short-term SOM is a source of
  nitrogen, phosphorus, and sulfur for plants.
  Short-term SOM lasts 1 to 3 years.
• Long-term SOM (humus) is the carbon form that
  resists decomposition and may last for greater
  than 1000 years.
• Soil carbon losses are exacerbated through
  erosion and, to a lesser extent, may be lost
  through leaching of dissolved organic carbon
  (DOC).
• The basic processes of the carbon cycle are CO2
  in through photosynthesis, and CO2 out through
  decomposition.

8
Soil Organic Matter

• Organic matter encompasses
  all organic components of a soil
• Fresh residues
• Decomposing organic matter
• Stable organic matter
• Living organisms

9
Fresh Residues

• Up to 15 of organic
  matter is fresh residue
• Comprised mainly of
  litter fall
• Much can be recognized
  as plant residue

10
Harvest index (HI)(rules-of-thumb)
Source of Fresh Residues

• HI grain yield / biological yield
• Biological yield grain yield stover yield

Corn 0.50 to 0.55 Wheat 0.40 Soybean 0.40 to
0.45 Sorghum 0.48
11
Carbon / Nitrogen Ratio
High C/N ratio
Low C/N ratio
Legume
Corn

• Decomposition is rapid due to higher nitrogen
  within the plant.
• Microorganisms are satisfied with plant N. When
  microorganisms die, nitrate and ammonia are
  released, increasing soil N.

• Decomposition is slower.
• Microorganism will deplete soil of nitrate and
  ammonium until they die and release nitrate and
  ammonium.

12
Carbon / Nitrogen Ratio

• Carbon / Nitrogen (C/N) ratios are important.
  Plant and animal residues that have a C/N of 301
  and over, have too little N to allow for rapid
  decomposition. Therefore, the microorganisms
  will take ammonium and nitrate out of the soil to
  fuel decomposition. This depletes the soil of
  nitrate and ammonium. Plants and animal residues
  with low C/N ratios (201 and less) have
  sufficient N for the microorganisms to decompose
  the residues without taking from the soil.

13
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

14
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.
• Adequate levels of SOM can be maintained with
  proper fertilization, crop rotations, and tillage
  practices if crop residues are returned to the
  soil.

15
Soil Organisms

• A cubic meter of healthy soil
• home to billions of bacteria and fungi,
  millions of nematodes, tens of thousands of
  spring tails and mites and several hundred
  earthworms
• These "critters" are nature's recyclers,
  converting plant residue and animal manures into
  usable nutrients and soil organic matter.

16
Soil Organisms

• The soil microflora (bacteria, fungi and algae)
  are responsible for 90 of the decomposition of
  organic material.
• Plant residue is the main fuel for sustaining the
  broad spectrum of organisms residing in the soil.

17
Soil Organisms

• The microbial population can increase rapidly to
  take advantage of a favorable change in the soil
  environment, doubling in a few hours.
• The size of the microbial population is usually
  controlled by soil moisture, aeration,
  temperature and their distribution in the soil.

18
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)

19
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.

20
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

21
Stable Organic Matter

• Soil organic compounds become stabilized and
  resistant to further changes by microorganisms
• Bound inside soil aggregates
• Stabilized organic matter acts like a sponge and
  can absorb six times its weight in water

22
HUMUS

• Newly-formed humus
• combination of resistant materials from the
  original plant tissue
• compounds synthesized as part of the
  microorganisms' tissue which remain as the
  organisms die (Fluvic and Humic Acid)
• Humus is resistant to further microbial attack-
  N and P are protected from ready solubility.

23
Function of Humus

• holds water and nutrients
• it sticks together helps establish and maintain
  a strong crumb structure thus reduce soil
  erosion
• it 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

24
HUMUS STICKS SOIL PARTICLES TOGETHER HELPS
ESTABLISH AND MAINTAIN A STRONG CRUMB STRUCTURE
SANDY SOIL
CLAY SOIL
25
SOM Maintains soil Tilth

• aiding infiltration of air and water
• promoting water retention
• reducing erosion

26
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.

27
Can we change it?

• Residue management
• Removal
• Additions
• Manure (animal and green manure crop)
• Tillage
• Mixing
• Aeration

28
Can we change it? (continued)

• Crop selection
• Species
• Rotation or crop sequence
• Crop use (grain, forage, grazing)

• Management practices
• Irrigation
• Fertilization
• Pest control
• Planting time, planting density, etc.

29
Can you change it?
More disturbance
(Cambardella and Elliot, 1992)
30
Residue Management Study(1978-1983)

• Background
• Response to energy crisis of the 70s
• Objective (question)
• What is the affect of removing crop residues from
  (and adding residue additional to) the soil
  surface
• On soil properties?
• On crop production?

31
Residue Management Study
Over all years
(Wilhelm et al., 1986)
32
Residue Management Study
Soil Water
(Wilhelm et al., 1986)
33
Residue Management StudySoil organic matter
(0-30 cm)
After 8 yr of treatment application (cont. corn,
no tillage)
(Maskina et al., 1993)
34
Without Residue Management StudySummary
(production)

• Greater plant stress
• Less available soil water
• Greater soil temperature
• Decreased yield (50 removal)
• 13 reduction in grain yield
• 17 reduction in residue yield
• Yield reductions more closely related to soil
  water than soil temperature

35
Residue Management StudySummary (Soil organic
matter)

• Soil organic matter
• Changed linearly with residue application
• Remove 100 -5.7
• Remove 50 -3.4
• No removal -----
• Add 50 4.6

36
Clichés
Throwing rocks is easy! (Pat Gruber, CargillDo
LLC, Sept. 6, 20001)
However

• A bit of skepticism can be a good thing.
• You cant have your cake (soil organic matter)
  and eat (burn) it too.
• If it sounds too good to be true, it probably is.
• There are no free lunches.

37
Rules in the Real World

• Nature always bats last.
• Consequences of ignoring rules
• Today's solutions become tomorrow's problems.
  (Tom Franzen, Iowa Farmer)