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7/31/2019 Bab_08 Bahan Organik Tanah

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Chapter 8:

Soil Organic Matter

8.1


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Organic Materials: Biomass (plant roots,

organisms) Plant/animal/ Residue

(dead but identifiable:

twig, branches, log) Particle size > 2 mm

* Partly decomposedorganic materialsincluded microbes.

* Particle size < 2 mm

* 0 to 6% (by mass) inA horizons

*


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250 m

150 m

Light

Intermediate

50 mHeavy

SOM Soil + SOM

< 1.13 g cm-3

>1.3 g cm-3

Particle sizeParticle density

SOM:dark & light 8.3


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The Carbon Cycle

Organic matter decays CO2 is one of theimmediate products

Carbon is the common constituents of all OM and is

involved in essentially all life processesTransformation of this element is called as

Carbon Cycle ~ Biocycle ~ Cycle of life

That makes possible the continuity of life on the earth !

8.4


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Carbon cycleat plot level

Carbonate &

bicarbonates

CO2

CO2CO2

CO2

CO2

Food

Photosynthesis

CO2

MicrobiaNutrientrelease

Residue

Macrofauna

HumusLeaching

Nutrientrelease

Soilreaction

Soil

surfaceCO2

8.5


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C cycle at global / lanscape level

8.6


7/20Litter is worth!, sometimes it does not ! When?

8.7


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Role of SOM

Physic:

Bind mineral particles into granules

Maintain soil water content

Chemic:

Source of plant nutrients

Maintain Cation Exchange Capacity (CEC)

Detoxify poisonous elements

Biologic:

Energy Source for soil organisms8.8


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Litter (Serasah):

Dead leaf (Daun gugur )

Twigs (tangkai daun + ranting)

Branches (cabang)

Nutrient Source

Litter

Plant

Roots

8.9


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Coffee Monoculture,more weeding

Coffee Multistrata ~ thick

surface litter layer ~ lessweeding

P

hotographer:MikeChapman

Photographer:Ku

rniatunHairiah

8.10


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Water

75%

Drymatter

25%

O2

40%

Ash

8%

H

8%

C44% Carbohydr

ates

60%

Lignin

25%

Protein

10%

Fats,

waxes,

tannins

5%

Sugars & starches (1-5 %)

Hemicelluloses (10-30 %)

Celluloses (20-50 %)

Elemental

composition

Types of

compounds

Composition of green plant materials addedto soils (Organic materials)

Inorganicelements

8.11

CO


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CO2

60-80 %

Organic

residues100 g

10-

30%

3

8

%

3

8

%

Complex humicNon-humic :polysacharids,polyuronides, acids etc.

Biomass(soilorganisms)

Humus (15-30 %)

8.12


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Factors affecting soil organic matter

Climatic: Temperature, rainfall

Natural vegetation

Soil texture Soil has a high clay and silt

content, generally much high in soil organicmatter

Soil drainage poorly drained soils high insoil organic matter

Soil & crop management:

tillage, crop rotations etc.

8.13


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Forest Soil

Agicultural soil

Fertile Soil:

High SOM : ~ > 2.5 4.0 %Low Bulk Density: ~ < 1.3 g cm-3

High biota activity

Generally dark colored

8.14


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Serasah di Hutan

Cassava litter

Forest litter ~

various quality

How fast theorganic

materialsdecompose?

8.16


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O i M b kd i h i


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SOIL HUMUS

Compounds inorginal tissue

Organism numbers and rate of releaseof CO2 and H2O

CO2 & H2O release

Synthesis of new compounds

New soilhumus

level

Old soilhumus level

Fresh residuesaddedResidues well

humifiedTime

Organic Matter breakdown with time8.18


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Humus:

A mixture of complex compounds

Rather resistant mixture of brown or dark brown amorphous& colloidal organic substances

Result from microbial decomposition and synthesis

It has chemical & physical properties of great significance tosoils and plants

Major Characteristics of Humus

Tiny colloidal humus particles (micelles) are composed ofC, H, O.

The surface area of humus coloids per unit mass is veryhigh & negatively charge

8.19


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The maintenance of soil

organic matter in mineral

soils is the mostimportance challenge to

modern and traditional

agriculture alike.

Photographer : Suyanto, ICRAF, Bogor 8.20

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