Chapter 6. THE ORGANIC MATTER

AND THE SOIL ORGANIC MATTER The place of O.M. to sustain soil productivity

6.1. Introduction: how to understanding?, definition

6.2. The role of SOM in soil productivity

6.3. The classification of SOM

6.4. Organic fertilizer

(For Agro-technology Study Program – FAPERTA UNSOED)

Purwandaru Widyasunu

Soil Sciences Laboratory, Faperta, Unsoed.

2011. Copy in PDF by 2014.

6.1. Introduction, definition

The place of organic matter in providing sustainable

soil, what is mean???

Sustainable agriculture is not possible without sustainable soil. But soil

cannot be sustained without satisfactory SOM, which in turn is largely

dependent on OM additions and how they are handled.

The dependent of sustainable agriculture on organic matter originates

from the many beneficial effect of both OM and SOM forms.

SOM consist of wide variety of plant and

animal tissues in various stages of

decomposition. Various stage: fresh (non-decayed), slightly

decayed, the decayed, and finally forms THE HUMUS.

HUMUS is more stable than the organic

materials from which it is derived.

Humus is transitory in nature and will break

down, albeit very slowly, the rapidity

increasing in soils with ample oxygen and

good moisture levels and at elevated

temperatures.

Both OM and SOM are largely responsible for

soil formation and development.

What is implication of the soil development

on soil productivity???

6.2. The role of SOM in soil productivity

What processes can (we) hope with SOM??? Soil formation and development

The energy derived from the decay supports

the living microorganisms(bacteria, fungi,

actinomycetes). These organisms are constantly

modifying the rocks from which soil is formed, releasing

nutrient for plants.

The more benefit of energy: benefit to larger organisms

(mites, earthworm, and insects) that intimately mix the

fine rock fragments with OM, greatly hastening the

decomposition of the rock and speeding soil formation.

Maintaining large number of diverse of organisms, the OM

helps maintain balance a healthy balance between

beneficial and disease organisms.

The more benefits be hope

By SOM and added OM in soil:

The SOM and new OM supplies energy use for many useful

processes, without which it would become difficult IF NOT

impossible to provide satisfactory production.

Some important processes for agriculture supported by the

energy derived form OM:

1. The decomposition release slowly of nutrient for plant.

2. The SOM provide living N2 fixation microorganism from N

unavailable to N available to plant.

3. The sustenance of mychorrhiza fungi that help keep P in an

available form.

4. The support of bacteria, actinomycetes, and some filamentous

fungi that aid in the formation of cements so essential for

binding individual small soil particles into aggregates or peds.

THE SOM and added OM improves soil physic:

The aggregates formed greatly improved soil

structure and lessen soil bulk density.

The improved soil structure markedly improved crop

production by: 1. Improving water infiltration, thereby lessening soil erosion and

increasing the amount of available water.

2. Increasing air porosity, which allows better movement of air and

water in soils.

3. Providing an ideal environment for beneficial microorganisms and

plants roots.

4. Aiding good tilth, which is necessary for ease in soil preparation as

well as rapid development of seedlings and plants.

5. Reducing erosion by aiding infiltration, and favoring certain soil

characteristic that aid in the movement of suitable amounts of air

and water, WITHOUT which crop production is not possible.

THE OM aids soil productivity in several ways:

1. Increases cation exchange capacity (CEC), allowing

better retention of ammonium-N, K, Ca, and Mg.

2. Provides for chelation of several micro nutrients,

which helps keep them available.

3. Helps keep P available, particularly at both high and

low pH values.

4. Buffers soil, limiting rapid changes in pH or salt

content that can occur with addition of various

chemicals.

5. Decreases dispersion of soil by rain drops or

irrigation and thus lessen surface crust and

compaction.

6. Lessen changes in soil temperatures, which could

interface with nutrient availability and plant survival.

THE EFFECT OF OM AND SOM

thought to:

1. Soil physic

2. Soil chemistry

3. Soil biology

Through:

1. The energy supply produces

2. The carbon and other binding

agent supplies by OM

decomposition

3. The carbon, hormone, nutrient

affect soil biota.

6.3. The classification of SOM

Classification based on OM: size, age, maturity, source

Size: (i) very fine, (ii) fine, (iii) medium, (iv) coarse.

Age: (i) fibric (young), (ii) hemic (medium), (iii) sapric

(old containing humic acid).

Maturity: (i) immature, (ii) slightly mature, (iii)mature.

Can be defined by C/N; C/P; C/S

Source: from vegetation or animal; man made or

natural.

Basic Concept of Organic Matter

OM in soils can exist as:

1. Recently added materials called organic matter

(OM).

2. Decomposed materials beyond recognition, called

soil organic matter (SOM).

Factor affecting OM decomposition: 1. Factor of OM it self: (i) type of material (rich protein, cellulose, lignin,

etc.), (ii) age (young, old), (iii)particle size, (iv) N-content or C/N.

2. Factor out side OM: (i) soil moisture, pH, aeration, temperature,

nutrient content, (ii) weather: sub tropics, tropics, (iii) intensive

agriculture, soil/land/environment degradation.

6.4. Organic fertilizer

What is organic fertilizer:

Fertilizer is making from organic matter

made by human.

Source: plant, animal(fresh or waste).

Process composting aerobic or anaerobic.

The formation of humus-like material

outside the soil.

If composting in soil (by dug the soil) the

materials of animal waste (faeces and urine)

will become night-soil.

Test Range of analysis

C/N 6:1 – 20:1

pH 5-8

Conductivity 0.2 – 2 S/m

Total N 0.5-3.0 %

P 0.1-2.0 %

K

Ca

Mg

S

0.2-1.0 %

0.8-3.5 %

0.3-0.6 %

0.1-2.0 %

Variability of several important composition criteria of compost

(Wolf and Snyder 2002).

The mixing materials:

Need some care for mixing materials in composting to

have desirable product.

Need a balance of wide C/N ratio materials: straw,

stalks, brown leaves, wood chips, those to be mixed

with narrow C/N materials such as manure animal

residues, green leaves, legume hay, biosolids.

Make compost to C/N < 20; if < 12 or less that means

mature compost (ready to be used except of

pathogenic and heavy metals content are forbidden).

Use effective microorganism: LAB (lactic acid

bacteria) and IMO (indigenous microorganism).

The compost amount desire to increase soil

productivity.

Very good soil productivity can be maintained if sufficient OM is added each

year to maintain adequate porosity, allow sufficient water storage and

movement, limit erosion, increase nutrients.

Guatemala soils case: 1 % org-C loss as CO2 equal to 20,000 lb dry

matter/acre. That means 65 % loss of org-C during decomposition process,

leaving only 35 % as SOM. Thus it needs 57,000 lb of OM to be added per

acre to replace the loss 1.0 percent.

Source:

Benjamin Wolf and George H. Snyder. 2002. Sustainable Soils: The Place of Organic

Matter in Sustaining Soils and Their Productivity. The Haworth Press, Inc.