organic matter decomposition


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organic matter decomposition

  2. 2. Outline • • • • Process of organic matter decomposition Factors affecting organic matter decomposition Significant to microorganism Basic plant
  3. 3. SOIL • • • • Properties of soil Microorganisms in the soil Plant nutrients in the soil Sources of plant nutrients in the soil • Basic plant nutrient cycle
  4. 4. 1) Properties of soil • There are 3 major properties of soil:  Physical- soil structure and texture  Chemical-chemical component; 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.
  5. 5. 2) Microorganisms in the soil • Contain 5 major groups of microorganism:      Bacteria Actinomycetes Fungi Algae Protozoa
  6. 6. 2) Microorganisms in the soil • All these microorganism 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
  7. 7. 3) Plant nutrients in the soil • 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 (O2), (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)
  8. 8. 4) Sources of plant nutrients in the soil 1) Weathering of soil minerals 2) Decomposition of plant residue, animal remains and soil microorganisms 3) Application of fertilizers and limiting materials 4) Application of manures, composts, biosoilds (sewage sludge) and other organic amendments
  9. 9. 4) Sources of plant nutrients in the soil 5) N-fixation by legumes 6) Ground rock powders or dusts including greensand, basalt and rock phosphate 7) Inorganic industrial by-products 8) Atmosphere deposition, such as N and S from acid rain or N-fixation by lightning discharge 9) Deposition of nutrient rich sediment from erosion and flooding
  10. 10. 5) Basic Plant Nutrient Cycle
  11. 11. 5) Basic plant Nutrient Cycle • The basic nutrient cycle highlights the central role of soil organic matter and microorganisms. • Cycling of many plant nutrients, especially N,P, S, and micronutrients, closely follows the carbon cycle. • Plant residue and manure from animals that are fed forage, grains, and other plant derived foods are returned to the soil.
  12. 12. 5) Basic plant Nutrient Cycle • This OM pool of carbon compounds becomes food for bacteria, fungi and other decomposers. • As OM is broken down to sampler 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.
  14. 14. DECOMPOSITION OF OM • Definition:  Breakdown of dead plant and animal material and release of inorganic nutrients  Decomposition is a biological breakdown and biochemical transformation of complex organic molecules of dead material into simpler organic and inorganic molecules (Juma, 1998).
  15. 15. Decomposition (and respiration)
  16. 16. SOURCE OF ORGANIC MATTER • • • • Plant remains Animal tissue and excretory products Cells of microorganisms However, plant is the main contribution to OM.
  17. 17. ORGANIC CONSTITUENTS OF PLANTS 1) 2) 3) 4) Cellulose most abundant 15 to 60% of dry weight. Hemicellulose, 10 to 30 % Lignin, 5 to 30% Water soluble fraction include simple sugar, amino acids, aliphatic acids, 5 to 30 % of tissue weight 5) Ether and alcohol-soluble constituents; fats, oils, waxes, resins and a number of pigments. 6) Proteins
  18. 18. WHY ORGANISMS 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.
  19. 19. 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.
  20. 20. WHO ARE THE DECOMPOSERS? A.    SOIL FAUNA earthworms, arthropods Fragmentation (cominution) increases surface area. Distributes OM within soil profile B. SOIL MICROORGANISM  Heterotrophic bacteria, fungi  Derive energy, carbon and nutrients from dead OM in the process they release CO2 through respiration. RESPONSIBLE FOR BULK OF DECOMPOSITION!
  21. 21. DECOMPOSITION PROCESS • THREE MAIN PROCESSES: 1) ASSIMILATION  Conversion of substrates materials into protoplasmic materials  E.g. OM carbon to microbial carbon  E.g. protein to microbial protein 2) MINERALIZATION  Conversion of organic substance to inorganic form.  E.g. protein from OM will be converted to inorganic nitrogen in the soil. 3) IMMOBILIZATION  Conversion of inorganic form into organic.  E.g. inorganic nitrogen from the soil converted into microbial protein.
  22. 22. FACTORS AFFECTING RATE OF DECOMPOSITION TEMPERATURE • Microbial activity responds exponentially to increased temperature until enzymes denature, etc. MOISTURE • Microbial activity has optimum moisture • Low moisture = dessication, slow diffusion • High moisture = low O2 availability; no lignin degradation pH • Most microbes exhibit optimum activity near pH 7. • Fungi most active in acid soil and bacteria in moderate soil pH.
  23. 23. WHAT IS THE C:N RATIO? • The carbon-to-nitrogen (C:N) ratio is often used as an indication of mineralization or immobilization whether will occur. • The C:N ratio is the total concentration of C divided by the total concentration of N.
  24. 24. 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
  25. 25. • The C:N ratio is the most commonly used in soils because N is the most limiting elements. • 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 = 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
  26. 26. C:N RATIO 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 range • When 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
  27. 27. SUBSTRATE QUALITY:CARBON • Different carbon compounds are decomposed at different rates.  Cellulose faster  Lignin 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.