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ORGANIC MATTER DECOMPOSITION CHAPTER 6

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ORGANIC MATTER DECOMPOSITION. CHAPTER 6. OBJECTIVES. Process of organic matter decomposition Factors affecting organic matter decomposition Relate the activities of microorganism with soil fertility. SOIL. There are three major properties of soil. Physical – soil structure and texture - PowerPoint PPT Presentation

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Page 1: ORGANIC MATTER DECOMPOSITION

ORGANIC MATTER DECOMPOSITION

CHAPTER 6

Page 2: ORGANIC MATTER DECOMPOSITION

OBJECTIVES

Process of organic matter decomposition

Factors affecting organic matter decomposition

Relate the activities of microorganism with soil fertility

Page 3: ORGANIC MATTER DECOMPOSITION

SOIL

There are three major properties of soil.There are three major properties of soil.

Physical – soil structure and texture

Chemical – chemical components; pH, nutrients

Biological – micro and macro fauna/flora

Soil organic matter (OM) is any material produced originally by living organisms (plant or animal) that is returned to the soil and goes through the decomposition process

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Contain five major groups of microorganisms

Bacteria

Actinomycetes

Fungi

Algae

Protozoa

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All these microorganisms participate in the various activities that take place in the soil.

Among the activities are;

Decomposition of organic matter

Nutrient Cycling

Nutrients transport/flow

Protection

Page 6: ORGANIC MATTER DECOMPOSITION

There are at least 16 essential chemical elements for plant growth

Plant must have these nutrients to performance the various physiological functions

C, H and oxygen (O), (from air & water)

N, phosphorus (P), potassium (K), Ca, Mg, sulfur (S), iron (Fe), manganese (Mn), Zn, copper (Cu), boron (B), molybdenum (Mo), and chlorine (Cl) (from soil)

Sodium (Na), silicon (Si), and nickel (Ni) Cobalt (Co) (required by certain plants)

ESSENTIAL PLANT NUTRIENTS

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SOURCES OF PLANT NUTRIENTS IN THE SOIL

1) weathering of soil minerals 1) weathering of soil minerals

2) 2) decomposition of plant residues, animal remains, and soil microorganisms

3) application of fertilizers and liming materials, 3) application of fertilizers and liming materials,

4) 4) application of manures, composts, biosolids (sewage sludge) and other organic amendments

Page 8: ORGANIC MATTER DECOMPOSITION

5) N-fixation by legumes

6) ground rock powders or dusts including greensand, basalt, and rock phosphate

7) inorganic industrial byproducts

8) atmospheric deposition, such as N and S from acid rain or N-fixation by lightning discharges,

9) deposition of nutrient-rich sediment from erosion and flooding

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Basic Plant Nutrient Cycle

The basic nutrient cycle highlights the central role The basic nutrient cycle highlights the central role of soil organic matter and microorganisms. of soil organic matter and microorganisms.

Cycling of many plant nutrients, especially N, P, S, Cycling of many plant nutrients, especially N, P, S, and micronutrients, closely follows the Carbon and micronutrients, closely follows the Carbon Cycle. Cycle.

Plant residues and manure from animals that are fed forage, grain, and other plant-derived foods are returned to the soil.

Page 11: ORGANIC MATTER DECOMPOSITION

This OM pool of carbon compounds becomes food for bacteria, fungi, and other decomposers.

As OM is broken down to simpler compounds, plant nutrients are released in available forms for root uptake and the cycle begins again.

Plant-available nutrients such as K, Ca, Mg, P, and trace metal micronutrients are also released when soil minerals dissolve.

Page 12: ORGANIC MATTER DECOMPOSITION

DECOMPOSITION OF OM

Definitions:

Breakdown of dead plant and animal material and release of inorganic nutrientsDecomposition is a biological process that includes the physical breakdown and biochemical transformation of complex organic molecules of dead material into simpler organic and inorganic molecules (Juma, 1998).

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SOURCE OF ORGANIC MATTER

Plant remains

Animal tissues and excretory products

Cells of microorganisms

However, plant is the main contributor to OM

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ORGANIC CONSTITUENTS OF

PLANTS1. Cellulose, most abundant 15 to 60% of dry weight2. Hemicelluloses, 10 to 30%3. Lignin, 5 to 30%4. Water soluble fraction include simple sugar, amino

acids, and aliphatic acids, 5 to 30% of tisue weight5. Ether and alcohol-soluble constituents; fats, oils,

waxes, resins and a number of pigments6. Proteins

Page 16: ORGANIC MATTER DECOMPOSITION
Page 17: ORGANIC MATTER DECOMPOSITION

WHY MICROORGANISMS DECOMPOSE OM

Supplying energy for growth

Supplying carbon for new cell synthesis

The cells of most microorganisms commonly contain approximately 50% carbon. This is derived mainly from the substrates.

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WHY DO WE CARE ABOUT DECOMPOSITION?

Decomposition is important in releasing nutrients tied up in dead organic matter

and return it back to the soil.

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WHO ARE THE DECOMPOSERS?

A. Soil fauna (e.g., earthworms, arthropods): physicalicalfragmentation (cominution) increases surface area,fragmentation (cominution) increases surface area,distributes OM within soil profile, doesn’t alter litter distributes OM within soil profile, doesn’t alter litter chemistrychemistry

B. Soil microorganisms: heterotrophic bacteria and B. Soil microorganisms: heterotrophic bacteria and fungifungiderive energy, carbon, and nutrients from dead OM; in the process they release CO2 through respiration;

RESPONSIBLE FOR BULK OF DECOMPOSITION!!

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DECOMPOSITION PROCESSES

There are three main processes

1. Assimilation = conversion of substrate materials into protoplasmic materials. Eg. OM carbon to microbial carbon. Protein to microbial protein.

2. Mineralization = conversion of organic substance to inorganic form. Eg. Protein from the OM will be converted to inorganic nitrogen (NH4, NO3) in the soil.

3. Immobilization = conversion of inorganic form into organic form. Eg. Inorganic nitrogen from the soil converted into microbial protein.

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FACTORS AFFECTING RATE OF

DECOMPOSITION1. Temperature

Microbial activity responds exponentially to increased temperature until enzymes denature, etc.

2. MoistureMicrobial activity has optimum moistureLow moisture = desiccation, slow diffusionHigh moisture = low O2 availability; no lignin degradation

3. pHMost microbes exhibit optimum activity near pH 7.Fungi most active in acid soil and bacteria in moderate soil pH.

Page 24: ORGANIC MATTER DECOMPOSITION

Different carbon compounds are decomposed at different rates.

Cellulose fasterLignin slower decomposition as compared to cellulose.

C:N of the OM determine the rate: high slower, this is due to insufficient of N for microorganisms to assimilate carbon; low faster, nitrogen is sufficient for rapid assimilation of carbon.

Substrate Quality: Carbon

Page 25: ORGANIC MATTER DECOMPOSITION

The carbon-to-nitrogen (C:N) ratio is often used as an indication of whether mineralization or immobilization will occur.

The C:N ratio is the total concentration of C divided by the total concentration of N.

WHAT IS THE C:N RATIO?

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C:N RATION RANGE

Because there is a suite of microorganism and OM quality, generally we can predict whether mineralization or immobilization will take place base on the C:N ration rangeWhen surface of soil layer have a:

C:N > 30:1 => immobilization highly likely to occur

C:N < 20:1 => mineralization is likely to occur

C:N between 20-30:1 => both processes may occur but will generally in balance

Page 27: ORGANIC MATTER DECOMPOSITION

C:N OF SOME ORGANIC MATTER

Organic Matter C:N Ratio

legumes 13 – 25:1

manure 20 - 30:1

straw 80:1

sawdust 400 – 600:1

microorganisms 5 – 10:1

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The C:N ratio is the most commonly used in soils because N is the most limiting element. A microbe with a C:N ratio of 8:1 would require OM with a C:N ratio of 24:1.The C:N ratio in lower in microorganisms and = 8.Since microbes incorporate only about 1/3 of the C metabolized into biomass, the substrate material must have C:N ratio = 24 to satisfy the N requirement of microbes. If the C:N ratio > 24, available soil N is consumed by microbes and plant available N decrease.