Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Soil organic matter pkm

6,894 views

Published on

Soil organic matter, genesis, classification and options for carbon sequestration in soil

Published in: Education, Technology, Business
  • Be the first to comment

Soil organic matter pkm

  1. 1. Soil Organic Carbon All availed amenities by industrialized societies are based on fossil fuel derived energy. Thus, the modern civilization can be appropriately termed “the Carbon Civilization” or the C-Era (Rattan Lal,2007), The modern civilization is dependent on C-based energy sources. It is literally hooked on carbon, and in need of a big-time rehabilitation.
  2. 2. N C P K Ca Mg S Zn Cl Mn Carbon is a “keystone” Bo Building of agriculture
  3. 3. Nutrient cycling requires carbon! Carbon is the “Lord of the Rings” C H2O K P S Cl Mg Ca Zn N Bo Mn Mo Cu Fe Na
  4. 4. ORGANIC MATTER The living, the dead and the very dead Roots, micorrhizae and bacteria Humus Crop residues, dead roots, microbial biomass stabilized OM
  5. 5. AVERAGE SOIL COMPOSITION 25% Water { Pore space 50% 25% Air 45% Inorganic (mineral materials) } Solids 50% 5% Organic Matter Mechanical Strength = f (Bulk density, Aggregation, Water content)
  6. 6. Soil Organic Matter Composition Soil organic matter 1-6% of total soil mass Soil Mineral particles Readily decomposable 7-21% Soil microbial biomass 3-9% of total SOM mass Fauna 10% Bacteria & actinomycetes 30% Stable (humus) 70-90% SOM as a “revolving nutrient fund” Fungi 50% Yeast, algea, protozoa, nematodes 10%
  7. 7. Relative C content (g C m-2) Soil Organic C Dynamics P = net primary production Conversion to cultivated agriculture Original accumulation D = decomposition Adoption of conservation practices loss sequestration P>D P<D P>D Time prairie agroecosystem (Janzen et al., 1998)
  8. 8. Role of soil Organic matter
  9. 9. Effect of organic matter on available soil water Organic matter is another soil property that has a large influence on plant available water. As we saw with clay, increasing organic matter increases the amount of water held in soil both at wilting point and at field capacity. Since the increase in field capacity is greater than the increase in wilting point, plant available water increases as organic matter increases. This is because, like clay, a small amount of stable soil organic matter has extremely high surface area. Soil organic matter behaves much like a sponge as it soaks up large amounts of water that roots can squeeze back out again. As we will see soon, organic matter is also important for other aspects of soil
  10. 10. SOM: What is it? SOIL ORGANIC MATTER Living Organisms: BIOMASS Dead Oi tissues and wastes: DETRITUS Oa Non-living, non-tissue: HUMUS
  11. 11. Humic substances Solubility Colour Degree of polymerisation Molecular Weight Carbon (%) Oxygen (%) Fulvic acid Alkali and acid soluble Yello low w brown Low 45 48 Humic acid Alkali soluble acid insoluble Dark moderate brown Moderate 50 40 Humin Alkali and acid insoluble black High 62 30 high Humus is a complex and rather resistant mixture of brown amorphous and colloidal susbstances modified from the original tissues or synthesised by the various soil organisms
  12. 12. When Organic tissue is added to aerobic soil, 3 general reactions takes place 1.The bulk of the material undergoes enzymatic oxidation with CO2, water , and heat as the major products. And also decomposer biomass is produced. 2. The Nutrient elements, N, P, and S etc. are released and /or immobilized by element specific reactions. 3. Compounds resistant to microbial action are formed (lignin) by degradation and/or synthesis reactions Decomposition: An oxidative process: In aerobic decomposition , a major portion of all these compounds undergoes essentially a “burning” or oxidation process. Organic matter is a potential energy source; A soil containing 4% of O.M. Carries 150-180 million kilocalories of potential energy/acrefurrow slice. This is equivalent in heat value perhaps to 20-25 tons of anthracite Coal.
  13. 13. How does anaerobic differ from aerobic decomposition? Decomposition proceeds most rapidly with O2 as the electron acceptor Anaerobic decomposition releases relatively little energy Products of anaerobic decomposition are partially oxidized organic compounds (organic acids), alcohols, CO2, and methane (high energy products) Methanogenic bacteria and Archaea (Archaea)
  14. 14. mposition of Organic Matter Form Formula Cellulose Decomposition (C6H10O5)n Composition rapid * 15-50% Hemicellulose glucose 5-35% C6H12O6 moderate-slow C5H10O5 moderate-slow galactose mannose xylose Lignin(phenyl-propane) slow Crude Protein rapid RCHNH2COOH** 15-35% 1-10% Polysaccharides Chitin (C6H9O4.NHCOCH3)n rapid Starch glucose chain rapid Pectins galacturonic acid rapid Inulin fructose units - decomposition more rapid in the presence of N ** - amino acid glycine (one of many building blocks for proteins)
  15. 15. Cellulose Structure • Simple, repeating structure – Polymer of Glucose units – “Easy” to decompose
  16. 16. Lignin structure • Complex, nonrepeating structure – Phenyl rings – Harder to decompose – Need lots of enzymes to do it Only a few microbes can break them (e.g., white-rot fungi)
  17. 17. Factors affecting decomposition of organic matter
  18. 18. K-strategists (high affinity constants for specific resistant compounds) have an advantage when soil is poor in easily digested compounds . With residue input r-strategists (opportunistic) will rapidly multiply . Intense microbial activity can stimulate humus breakdown (priming effect) . As easy residue is lost r-strategist die and bodies are
  19. 19. Most of the carbon released during the initial rapid breakdown of the residues is converted to CO2, but smaller amounts of Carbon are converted into microbial biomass (and synthesis products) and, eventually, into soil humus. The peak level of microbial activity appears to accelerate the decay of the original humus, a phenomenon known as priming effect.
  20. 20. Nitrogen mineralisation process Protein & allied Compound undergoes mineralization in three steps, viz., Aminization, Ammonification, Nitrification Aminization : (Protein → Proteose → Peptone → Peptide → Amino acid compd) Proteins R- NH2 + CO2 + energy + other products Ammonification : (R-NH2 + H2O → R – OH + NH3 + E by enzymatic hydrolysis) H 2O NH4+ + OHThe relesaed (NH4+) is subject to following changes: Nitrification: (i) 2NH+4 +3O2 → 2NO2 +2 H2O + 4H+ + 66 KCal (enzymatic oxdn) Nitrosomonas europae 2NO2- + O2→ 2NO3- + 18 KCal (enzymatic oxdn) Nitrobacter winogradskii (ii) It (NH4+) may be absorbed directly by plants (iii) It (NH4+) may be fixed by lattice of expanding type clay mineral
  21. 21. Significance of C:N ratio C:N ratio in arable soil is 10:1 whereas ratio in plant material is variable, ranging from 20:1 to 30:1 (legumes, Farm manure) to as high as 100:1(straw), microbes 10:1 The C:N ratio in SOM is important for two major reasons; a) keen competition for available N results when residues having a high C:N ratio are added to soils, and b)because this ratio is relatively constant in soil, the maintenance of Carbon-and hence soil organic matter-is dependent on the soil Nitrogen level.
  22. 22. 80 60 Net Immobilization C:N 40 Net Mineralization 20 0 4 to 8 Weeks NO 3 - CO Evolution 2 New NO Level 3- Amount CO 2 Time Cultivation and addition of straw, N immobilization & mineralization of N, evolution of CO 2
  23. 23. Practical example: Assume that a representative cultivated soil in a condition favouring vigorous nitrification is examined. Nitrates are present in relatively large amounts and the C:N ratio is narrow . The general purpose decay organisms are at a low level of activity, as evidenced by low carbon-di-oxide production. Now, suppose that the large quantities of organic residues with a wide C:N ratio (50:1) are incorporated in the soil under conditions supporting vigorous digestion. A change quickly occurs. The heterotrophic flora-bacteria, fungi, and actinomyctes - become active and multiply rapidly, yielding CO2 in large quantities. Under these conditions, nitrate nitrogen practically disappears from the soil because of the insistent microbial demand for this element to build their tissues. And for the time being, little or no N , is in a form available to higher plants. As decay occurs, the C/N ratio of the plant material decreases since C is being lost and N conserved. This condition persists until the activities of the decay organisms gradually subside due to lack of easily oxidisable Carbon. Their number dercrease, CO2 formation drops off, N ceases to be at a premium and nitrification can proceed. Nitrates again appear in quantity and the original conditions again prevail except that, for the time being, the soil is somewhat richer both in nitrogen and humus.
  24. 24. High CN added Immobilization of N. Nitrate depression until all easy C is gone and activity drops and microbes die. N mineralization Low CN added N is present to meet microbial needs; thus, do not immobilize N
  25. 25. Effect of C:N on rate of decomposition
  26. 26. Holding carbon in the soil!
  27. 27. Soil Carbon “C” : easy come, easy go! Deep plowing of organic matter might increase Carbon storage for the upper foot of soil. Gaining Carbon Conservation tillage and cover crops may result in net carbon sequestration. Losing Carbon Intensive tillage results in carbon loss.
  28. 28. Ten Options of Sustainable Management of Soils 1. Retain crop residue as mulch. 2. Adopt no-till farming. 3. Include leguminous cover crops in the rotation cycle. 4. Maintain a positive nutrient balance INM (e.g., manure, compost). 5. Use precision farming/site specific management.
  29. 29. Ten Options (continued) 6. Conserve water through sub/drip irrigation and water harvesting. 7. Restore marginal/degraded/desertified soils. 8. Grow improved/GM plants along with agroforestry measures. 9. Integrate principles of watershed management. 10. Restore wetlands.
  30. 30. Sustainability of a Land Use System S1 = CNPP n (Σ Ci) i=1 S1 = Sustainability index of a land use system CNPP = C output as net primary productivity Ci = C input from all factors of production
  31. 31. Soil is meant to be covered. Manage soil carbon - make the world a better place.
  32. 32. A Precious Resource Irrespective of the climate debate, soil quality and its organic matter content must be restored, enhanced and improved.
  33. 33. Soil and the Life-Cycle of Civilizations How long would it take to erode 1 m thick soil? Thickness of soil divided by the difference between Rate of soil production and erosion. 1m 1mm - .01 mm ≈ 1000 years This is about the life-span of most major civilizations...
  34. 34. A nation that destroys its soils, destroys itself. – President Franklin D. Roosevelt, Feb. 26, 1937. National Archives: 114 SC 5089
  35. 35. Let the Hundred flowers bloom Prepare yourself thoroughly
  36. 36. Fossil carbon cycle. Biological carbon cycle. Atmospheric Carbon as CO2 CO2 Energy from fossil fuels CO2 Energy from bio-fuels CO2 C Plant biomass and roots left on or in the soil contribute to Soil Carbon or Soil Organic Matter and all associated environmental and production benefits. Nonrenewable Renewable

×