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N Reservoir  Biosphere (living organisms)   Hydrosphere (water)   Atmosphere (air)  Geosphere PowerPoint Presentation
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N Reservoir  Biosphere (living organisms)   Hydrosphere (water)   Atmosphere (air)  Geosphere

N Reservoir  Biosphere (living organisms)   Hydrosphere (water)   Atmosphere (air)  Geosphere

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N Reservoir  Biosphere (living organisms)   Hydrosphere (water)   Atmosphere (air)  Geosphere

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  1. Where is the N on planet earth ?? N Reservoir Biosphere (living organisms)  Hydrosphere (water)  Atmosphere (air) Geosphere  Crust     Soils and Sediments     Mantle and Core MegaTons2.8 x 1052.3 x 1073.86 x 1091.636 x 1011 0.13 - 1.4 x 10100.35 - 4.0 x 1091.6 x 1011 % of Total0.0002 0.014 2.3 97.7 0.78-8.4    0.21-2.4    95.6  Most of the N is deep within the earth but very little of this N participates in biological cycles.

  2. Biologically relevant N % of BR N<0.01      < 1%      ~ 8 %  > 90 % MegaTons2.8 x 1052.3 x 1070.35 x 109 3.86 x 109 % of Total     0.0002      0.014      0.21     2.3 Reservoir/Pool Type Biosphere  Hydrosphere  Soil  Atmosphere 

  3. N has two stable isotopes, 14N and 15N. 14N is much more abundant than 15N 15N labeling can be used to track the fate of added N

  4. Why is N2 so unreactive ??? N2 is chemically unreactive at the temperatures and pressures of the hydrosphere, biosphere, and atmosphere because of its triple bond. This triple bond can only be broken under extreme temperatures and or pressures or in the presence of select enzymes.

  5. Reactive N Reactive N Reactive N Reactive N

  6. ~ 5 MT ~ 20 MT ~ 30 MT ~ 85 MT > 90 MT

  7. Human activities now dominate global cycling of reactive N

  8. Nitrogen has many different oxidation states ! C-NH2 Organic N Plant metabolism Most reduced Poorly drained soils Most oxidized Well aerated soils

  9. Do any of you remember this view ??? Ammonium nitrate + diesel fuel Nitrate is a powerful oxidizing agent Why is this combination explosive ? April 19, 1995 - Alfred P. Murrah Federal Building

  10. The on-going process of N shifting from one form to another is collectively called the N cycle Soil Microbial biomass Plant biomass Plant uptake

  11. Why do plants need N ? Nitrogen is an integral component of many essential plant compounds Amino acids Proteins Nucleic acids Chlorophyl 2.5 - 4% of plant dry matter enzymes

  12. Old leaves first Evidence of N Deficiency yellowing (chlorosis) that starts at the tip and moves in along the midrib These symptoms should not be used to identify where N is needed. Major irreversible yield loss has already occurred when these symptoms are present

  13. Nitrogenase: the key to biological N fixation

  14. Only way that N “fixation” can occur at low temperatures and pressures Substantial energy input is still required ~ 8 lbs of C per lb of N fixed

  15. Legume nodules come in many shapes and sizes

  16. Soybean has its own inoculation group

  17. Not all legumes are efficient N fixers ! Efficient N fixation forage legumes, soybeans cowpeas, peanuts Inefficient N fixation snap beans garden peas lima beans

  18. Nitrification NH4+ NO3- NO2- Nitrification is actually a multi-step process NO2- is a toxic intermediate product Warm, aerated, near neutral conditions promote rapid nitrification


  20. Nitrification inhibitors are not 100% effective and are only cost-effective in some situations

  21. Denitrification NO3-     NO2-     NO     N2O     N2 Warm, anaerobic conditions + OM promote rapid denitrification

  22. Why is nitrate such a slippery character ? • Nitrate is an anion • Nitrate compounds are very soluble • Nitrate is next in line as an electron acceptor • when O2 is not present

  23. Immobilization

  24. Net mineralization Net immobilization

  25. N is often a limiting nutrient Potential N uptake by wheat pasture Mineralized soil N Jenkinson

  26. Well-fertilized crops often obtain more than half of their N from SOM Where does the N come from ? Why more soil N? Magdoff and Weil (2003)

  27. Effect of tillage and crop on mineralizable N Mineralizable N declines during grass crops Mineralizable N increases during soybeans Wheat Soybeans Sorghum Adapted from Magdoff and Weil (2004)

  28. What happens to fertilizer N ? 100 Environmental losses during growing season 90 80 Which N rate is likely to result in the most leaching over the winter? Measured after harvest

  29. N rates applied to corn in the US have been relatively stable for 3 decades

  30. Corn yields have increased steadily since ~ 1940 160 bu/acre

  31. Weather often regulates crop productivity more than nutrient input rates in high productivity systems

  32. As a result… Yield per unit of N has increased over the last 30 years ? lbs of grain per lb of N Some farmers consistently harvest more than 75 lbs of grain for each lb of N applied

  33. Can we manage for the variable amount of N supplied by soil ?

  34. Why don’t most labs test for N ??? To the atmosphere 10-50 ? From the atmosphere 50 Crop uptake Fertilizer 200 200 Soil organic matter 4000 160 80 NO3- + NH4+ Microbial biomass Loss by leaching 20-100 ? Preseason mineral N is a poor predictor of in season availability of N in humid regions Total soil N is also a poor predictor of in-season availability of N

  35. PSNT

  36. Nitrogen credits for the pre-sidedress soil nitrate test (PSNT)   Benefit from added N is unlikely

  37. Researchers in many states have evaluated the PSNT and identified modifications that work well for specific crops and locations Click on this hot link:

  38. PY = Proven Yield method of determining N rate for corn Recommended N rate = Proven yield in bushels* 1.2 lbs of N/bushel – manure or legume credits

  39. Illinois Soil N test = Amino sugar test The soil sample is treated with sodium hydroxide solution in a Mason jar, then heated for five hours on a griddle at 48–50º C to convert amino sugar-N to gaseous ammonia. The ammonia is collected in boric acid-indicator solution and determined by titration.

  40. Amino sugar N No response to additional N

  41. No relationship between ISNT and EONR

  42. Relationship between ISNT and total SOM in Wisconsin • Strong correlation of ISNT values to soil organic matter (OM) shows that the ISNT is probably measuring a constant fraction of soil organic N rather than a readily mineralizable N pool University of Wisconsin-Madison Department of Soil Science 2006

  43. Research in NY Nitrogen (N) prices and environmental concerns have caused many corn (Zea mays L.) producers and advisors to rethink their current N management practices. These past 3 years, laboratory and field trials were conducted in NY to evaluate the performance of the Illinois Soil N Test (ISNT) in identifying whether or not additional N was needed. Initial test results showed the need for temperature control in the laboratory and resulted in a modification of the procedure to include enclosed boxes. Evaluation of the ability of the modified ISNT procedure in detecting increases in organic N upon compost and manure addition showed an increase in ISNT over time consistent with N credits from manure currently employed for N management in New York. However, to obtain an estimate of potential N release from readily available organic N sources, sampling shouldnot take place within 4-5 weeks after manure (or fertilizers that contain ammonium) application or sod or cover crop plowdown or chemical kill. Results of the first 3 years of field trials showed that soil samples taken to 20-cm (8 inch) depth and analyzed for both ISNT and LOI-OM can be used to predict the need for additional N for corn beyond starter fertilizer in New York

  44. Commercial labs that provide the ISNT There are several labs in the U.S. which currently run the amino sugar N test as part of their soil analysis services. By listing these labs we offer no endorsement of the labs. If you have questions about where to get your samples analyzed, please contact us for advice.