FORMATION AND COMPOSITION OF SOIL ORGANIC MATTER K R.pptx

FORMATION AND COMPOSITION OF SOIL ORGANIC MATTER K R.pptx

1. FORMATION AND COMPOSITION OF SOIL ORGANIC MATTER K R MICRO NOTES 1

2. Soil organic matter Soil organic matter is a organic component of soil consisting of plant and animal residues at various stages of decomposition. It also includes substances of organic origin either leaving or dead. K R MICRO NOTES 2

3. Role of soil organic matter It serves as a reservoir of nutrients for crops in the form of humus. It provides soil aggregation. It acts as food source for soil organisms. It increases the water holding capacity. It retains moisture. It contributes to the formation of course soil structure that lowers its erosion. It promotes soil aeration, cation exchange capacity and helps in maintaining soil pH. It increases bioavailability of dissolved minerals. K R MICRO NOTES 3

4. Formation of soil organic matter Soil organic matter is formed through the partial decomposition and transformation of plant input by soil organisms. Living organisms are composed of organic compounds and they secrete or excrete organic material into their environment by shedding body parts such as leaves and roots. After organisms die their bodies are broken down by microbial action (fungus and bacteria) Large molecules of organic matters can be formed from the polymerization of different parts of already broken down matter K R MICRO NOTES 4

5. The formation of soil organic matter depends on its origin, transformation mode, age and existing environment, thus its biophysiochemical functions vary with different environments. K R MICRO NOTES 5

6. Composition of soil organic matter Soil organic matter is composed mainly of Carbon, Hydrogen and Oxygen and has small amounts of other elements such as Nitrogen, Phosphorous, Sulfur, Potassium, Calcium and Magnesium. Animal and plant residues(earthworm, ants) Complex carbohydrates like Cellulose(20-50%), Starch(1-5%), Hemicellulose (10-30%), Pectin, Lignin, Tannins(10-30%) K R MICRO NOTES 6

7. Fats, oils, waxes, resins, mucilage (~1-10%) Alcohols, aldehyde, ketones, organic acids. Phenols, alkaloids, pigments, hydrocarbons and other products. Inorganic residues (mineral matter) Microbial biomass. K R MICRO NOTES 7

8. The 3 elements C, H and O makeup about 92% of the dry weight of the organic matter in soil. Other elements are very important for the nutrition of plants, including Nitrogen, Phosphorous, potassium , sulfur , calcium, magnesium and many micronutrients. These organic compounds include FATS are composed of glycerides of fatty acids like butyric acid, stearic acid and oleic acid also include C, O and H. CARBOHYDRATES contains C, H and O, it ranges from sugars to cellulose. LIGNINS they are complex compounds from the (wood) older parts and also include O,H and C. PROTEINS that include Nitrogen in addition to C, H, O and small amounts of sulfur, iron and phosphorus. CHARCOAL is elemental carbon that is derived from incomplete combustion of organic matter. K R MICRO NOTES 8

9. Soil organic matter is consist of three primary parts which includes small plant residues and small living soil organisms [Fresh] decomposing organic matter [Active] and stable organic matter [Humus]. Soil organic matter Plant residue and living organic matter (Fresh) Active organic matter (decomposing) Stable organic matter (Humus) K R MICRO NOTES 9

10. Fresh organic matter Fresh organic matter contains small plant residues and small living soil organisms Up to 15% of organic matter contains fresh residues It mainly comprised of litter (leaves), different types of plant litter can be seen K R MICRO NOTES 10

11. Active organic matter They are the portion that is decomposing. It helps microbial activity. They release nutrients into the soil. They are easy for microbes to digest and use for metabolism. Fresh crops residues are a good source of active organic matter. It contains sugar, oil, cellulose and proteins. It is excellent sources of energy and nutrients for soil organisms. It makes up 20 – 50% of soil organic matter. K R MICRO NOTES 11

12. Stable organic matter They are already decomposed compounds. They make up majority of soil organic matter (60 -90%). As soil organisms digest and decompose material, several things happens like The chemical nature of organic matter is modified. Nutrients are removed as microbes decompose the material. matter sticks to soil particles. It accumulates when active microbes are continuously decomposing organic matter. Thus soil organic compounds become stabilized and resistant to further changes by microorganisms. Stabilized organic matter acts like a sponge and can absorb water by 6 times its weight. K R MICRO NOTES 12

13. K R MICRO NOTES 13

14. Soil organic matter Inorganic substances/ matter Fulvic acid Organic substances /matter Unaltered materials Stable organic matter [humus] Non- humic substances Humic substances Humic acid humin K R MICRO NOTES 14

15. humus It is an organic matter which gradually decomposes in the soil. They are relatively stable, sticky mass of organic matter, chemical matter and microbes. It is chemically very complex and its composition varies with the location. Much of the available Nitrogen in the soil is bound up in humus and is released slowly as humus decays to simple compounds that disappears from the soil, this process is called mineralization. Besides nitrates the end products of mineralization are Carbon-di-oxide , water and such mineral ions as Calcium, magnesium and sul f ur . It is an old name for stable organic matter. Humus is a complex, stable pool of organic matter. The soil organic matter consists of 2 major groups namely 1) NON-HUMIC MATTER 2) HUMIC MATTER K R MICRO NOTES 15

16. Non- humic matter It contains unhumified residues of plant and animal. Alkali/Acid insoluble component of soil organic matter. It makes 20-30% of the soil organic matter. Composed of certain organic compounds like polysaccharides, proteins, fats, polymers like lignin's, polyuronides, waxes, resins, tannins and some compounds of low molecular weight. K R MICRO NOTES 16

17. HUMIC MATTER It is a brown- black colour humified residues Alkali/ Acid soluble component of soil organic matter. It makes ~60-80 % of the soil organic matter Composed of complex aerobic compounds (polyphenols, polyquinanes) Resistant to microbial biodegradation. Most active part of humus. K R MICRO NOTES 17

18. Based on their solubility they are classified into Fulvic acid (lowest molecular weight, alkali and acid soluble) Humic acid (medium molecular weight, alkali soluble and acid insoluble) Humin (highest molecular weight, usually insoluble in both alkali and acid except under most drastic conditions) K R MICRO NOTES 18

19. references Environmental microbiology by K Vijaya Ramesh Soil microbiology by N. S. Subba Rao Agricultural microbiology by G. Rangaswami and D.J . Bagyaraj T ext book of soil microbiology by T.V.S Prasad www.agroconection.com en.m.wikipedia.org www.fao.org nmsp.css.cornell.edu/publications/factsheets.asp(fact sheet 41 ) www.agric.wa.gov.au www.sciencedirect.com developments in soil science volume 3 openpress.usask.ca K R MICRO NOTES 19

20. Thank you K R MICRO NOTES 20