10 21 Nitrogen Cycle2

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10 21 Nitrogen Cycle2

  1. 1. Nitrogen Cycle Term: Legume
  2. 2. www.sciencedaily.com/releases/2009/04/090414110818.htm <ul><li>Go to sciencedaily.com & search for soybeans & aphids </li></ul><ul><li>Read the Article from April 20 th </li></ul><ul><li>Are rhizobia specific to legume species </li></ul><ul><li>Do naturally occurring rhizobia or commercially inoculated rhizobia provide better resistance? </li></ul><ul><li>Does the source of the rhizobia influence the effectiveness of nitrogen fixation? </li></ul>
  3. 3. Legumes <ul><li>Plants that have a symbiotic relationship with bacteria that grow in nodules on their roots. </li></ul><ul><li>Soybeans – widely rotated with corn crops to revitalize soil </li></ul><ul><li>Vetch & Clovers – Cover crops – green manure </li></ul><ul><li>Clovers & Alfalfa - grown to improve hay crops & pasture. </li></ul>
  4. 4. Other Legumes <ul><li>Red bud trees </li></ul><ul><li>Locust Trees </li></ul><ul><li>Beans </li></ul><ul><li>Peas </li></ul><ul><li>Most plants that form Pods </li></ul>
  5. 5. Rhizobia <ul><li>Rhizobia are specific to legume species </li></ul><ul><li>The naturally occurring bacteria were more effective at creating resistance against the aphid than the imported bacteria. </li></ul><ul><li>Older generations of rhizobia are more effective than the new ones </li></ul><ul><li>The rhizobia compete for space to grow on the roots </li></ul><ul><li>Naturalized rhizobia are as effective in nitrogen fixation as the commercial ones. </li></ul>
  6. 6. Nitrogen & Fertilizer <ul><li>Industrialized countries began producing chemical fertilizers after WWI </li></ul><ul><ul><li>Haber Process </li></ul></ul><ul><li>Manufactured nitrogen begins with the production of ammonia (NH 3 ). </li></ul><ul><li>Ammonia is a gas that is produced when atmospheric N 2 is combined with hydrogen from fossil fuels - also called anhydrous ammonia </li></ul><ul><li>Stored under pressure </li></ul><ul><li>When fuel prices ↑, fertilizer prices ↑ </li></ul>
  7. 7. Ammonia Fertilizers NH 3 Nitric Acid Sulfuric Acid Phosphoric Acid Carbon Dioxide Anhydrous Ammonia Ammonium Nitrate Ammonium Sulfate Ammonium Phosphate Urea
  8. 8. Nitrogen Fixation <ul><li>Conversion of Inert N 2 into bio-usable forms </li></ul><ul><li>atmospheric fixation by lightning </li></ul><ul><li>biological fixation by certain microbes </li></ul><ul><ul><li>alone </li></ul></ul><ul><ul><li>symbiotic relationship with some plants and animals </li></ul></ul><ul><li>industrial fixation – Haber Process </li></ul>
  9. 9. Nitrification <ul><li>Nitrification – whatever form of ammonia is applied to the soil, it must be converted to be used by plants </li></ul><ul><ul><li>NH 3 + Nitrosomonas -> NO 2 </li></ul></ul><ul><ul><li>NO 2 + Nitrobacter -> NO 3 </li></ul></ul><ul><li>NO 3 Very soluble form </li></ul><ul><ul><li>Only held loosely by soil colloids (clay & humus) </li></ul></ul><ul><ul><li>~ 5% of NO 3 dissolves in water and is lost by leaching </li></ul></ul>
  10. 10. Denitrification <ul><li>In saturated soils </li></ul><ul><li>Anaerobic Conditions (No oxygen) </li></ul><ul><li>Bacteria convert NO 3 to elemental Nitrogen (N 2 ) which is a gas and returns to atmosphere </li></ul><ul><li>30 -40% of applied Nitrogen if area has been flooded for 3-5 days </li></ul>
  11. 11. Volatilization <ul><li>Occurs when urea is converted to ammonium carbonate </li></ul><ul><li>Ammonium carbonate breaks down in warm moist soils to ammonia gas and carbon dioxide </li></ul><ul><li>Ammonia gas evaporates into the atmosphere. </li></ul>
  12. 12. Decay <ul><li>The proteins made by plants enter and pass through food webs just as carbohydrates do. </li></ul><ul><li>At each trophic level , their metabolism produces organic nitrogen compounds that return to the environment, chiefly in excretions. </li></ul><ul><li>The final beneficiaries of these materials are microorganisms of decay. </li></ul><ul><li>They break down the molecules in excretions and dead organisms into ammonia . </li></ul>
  13. 13. Carbon – Nitrogen Ratio <ul><li>The rate of decomposition of decaying plants depends on the C:N ratio </li></ul><ul><li>C:N ratios of 25:1 or less decompose quickly and make Nitrogen available to plants (mineralization) </li></ul><ul><li>C:N ratios of 25:1 or more cannot decompose with out drawing nitrogen out of the soil (immobilization) </li></ul><ul><li>Humus has a C:N ratio of 12:1 and has completely decomposed </li></ul><ul><li>Implications for mulch and composting </li></ul>
  14. 14. The Nitrogen Cycle <ul><li>N 2 - Nitrogen Gas 78% of air - Inert </li></ul><ul><li>NH 4 – Ammonium ion – Made by bacteria </li></ul><ul><li>NH 3 – Ammonia - Made by Haber-Bosch process. Industrial N fixation </li></ul><ul><li>NO 2 – Nitrite ion – Very toxic to plants – Bacteria convert it to Nitrate </li></ul><ul><li>NO 3 – Nitrate ion – Form used by plants Very soluble – quickly leaches out of soil </li></ul>
  15. 16. <ul><li>Video </li></ul>

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