1. Nitrogen

2. Nitrogen and Soil
The most limiting essential element in the environment
Surface soil range: 0.02 to 0.5%
0.15% is representative
1 hectare = 3.3 Mg
Atmosphere = 300,000 Mg as N2

3. Biological/Plant Nitrogen
Component of living systems
Amino acids
Proteins
Enzymes
Nucleic acids (DNA)
Chlorophyll
Strongly limiting in the Environment

4. Deficiency Chlorosis – pale, yellow-green appearance primarily
in older tissues.

5. Excess Enhanced vegetative growth – lodging
Over production of foliage high in N
Delayed maturity
Degraded fruit quality

6. Distribution/Cycling
Atmosphere
Soil / soil O.M.
Plants, animals
N2, NO, N2O
NH4+, NO3-, R – NH2
Proteins, amino acids
Organic Nitrogen (plant tissue, Soil Organic Matter): R – NH2
During organic decomposition, R – NH2 is usually broken down to NH4+
NH4+ is converted to NO3- by soil microorganisms

7. Forms: mineral and organic
Organic: plant/tissue N R-NH2
Mineral: soil N NH4+, NO3-
Cycling in the Environment
Mineralization: Decomposition of organic forms releasing
nitrogen into the soil, generally as NH4+
Immobilization: Plant uptake of mineral nitrogen, removing
it from the soil and incorporating into plant
tissue.

8. Ammonium R – NH2 NH4+ NH4+ or NO3- R – NH2 Mineralization
organic mineral
Immobilization
NH4+ or
NO3-
R – NH2

9. Organic and Mineral Nitrogen
Organic R – NH2
Mineral NH4+ , NO3-
mineralization
immobilization }
NH4+
Available to
plants
1-2% generally
available

10. Nitrogen in the Soil NH4+ NO3- Plant uptake Volatilization
Leaching
Nitrification
Adsorption/Fixation
NO3-

11. Adsorption and Fixation
NH4+
NH4+
Clay Colloid Or
Organic matter
Exchange
NH4+
NH4+
NH4+
Fixation

12. Nitrification NH4+ NO2- NO3- Aerobic (oxygen) Anaerobic (low oxygen)
Nitrosomonas
NO2-
nitrobacter
NO3-

13. Nitrate NH4+ NO3- NO2- NO3- Leaching to groundwater, surface water
Nitrosomonas
NO2-
nitrobacter
NO3-
(to plants)
NO3-
Leaching to groundwater, surface water
Loss of productivity
Environmental hazard

14. Environmental Impact NO3- NO2-
Methemoglobinemia – reduction by bacteria in ruminants and infants
NO3-
NO2-
Eutrophication – stimulation of algal growth, depletion of oxygen

15. Eutrophication Nitrogen Photosynthetic life O2 bacteria
They are rich in plant nutrients and thus their productivity is high. They produce high numbers of phytoplankton (suspended algae) which often cloud the water so that we have poor Secchi disk readings (average about 2.5 meters or 8.0 feet). These lakes also produce high numbers of zooplankton and minnows and other small fish that feed on the zooplankton. These small fish in turn provide food for the growth of larger fish. All in all, there is a high production of organic matter, like corn planted in rich soil. Much of this organic matter drifts to the bottom and forms a considerable depth of organic sediment. This sediment in turn provides the food for high numbers of bacteria. The descending plankton and the bacteria, through their respiration, can use up much or all of the oxygen from the lower depths of these lakes. Thus, one characteristic of eutrophic lakes is the summertime depletion of oxygen from the lower waters (below the thermocline – usually below about 5.5 meters or 18 feet during the summer months). Because of all of the phytoplankton produced, the eutrophic lake often has chlorophyll concentrations averaging about 14 mg/m3 or higher. The phosphorus concentration averages something over 80 mg/m3. Eutrophic lakes are often relatively shallow and often have weed beds. The weed beds are common because of the availability of nutrients and light to the shallow portions of these lakes, but also because the accumulated organic sediments provide the "soil" for their roots. Fishing is often quite good in eutrophic lakes; the high productivity of plankton and benthic (bottom) organisms in the shallows provide for relatively high numbers of fish with relatively good growth rates. Most of Michigan's eutrophic lakes are in the lower two-thirds of the Lower Peninsula.
bacteria

16. Unimpacted
N-impacted

17. Control Split applications Nitrification inhibitors
Slow release fertilizers
Cover crops
Encourage natural N fixation
NH4+
Nitrosomonas
NO2-
nitrobacter
NO3-

18. Nitrogen and Soil Atmosphere = 300,000 Mg as N2
The most limiting essential element in the environment
Surface soil range: 0.02 to 0.5%
0.15% is representative
1 hectare = 3.3 Mg
Atmosphere = 300,000 Mg as N2

19. Symbiotic Biological Nitrogen Fixation

20. Rhizobium Symbiotic Biological Nitrogen Fixation
Symbiosis between plant roots and rhizobium bacteria
Rhizobium

21. Atmospheric Nitrogen Fixation
N2 + 6H NH3
Fixing N2 is “expensive”
N N Triple bond
Must use energy to break these bonds
Haber - Bosch Process - Artificial Fixation of Nitrogen Gas:
200 atm oC
no oxygen
yield of 10-20%
Produces 500 million tons of artificial N fertilizer per year.
1% of the world's energy supply is used for it
Sustains roughly 40% of the population

22. Area to colonize = meristem Avenue of colonization = infection thread
Symbiotic Biological Nitrogen Fixation
Initialization
Plant roots send out signals inviting rhizobia to colonize the root
Rhizobia signal plants to produce an area in which they can colonize
The root produces the area and the avenue to colonize
Area to colonize = meristem
Avenue of colonization = infection thread
N2 + 6H NH3

23. Legume root hairs.
Chemical signals sent from
Root hairs to bacteria:
invitation to infect

24. Beginning of infection Rhizobium Root hair
Infection thread penetrates root cortex
Root hair

25. Root hair curls:
Traps bacteria

26. Nodules on legumes
Packed with N2-fixing
bacteria

27. Bacteroids in nodules Bacteroids: Rhizobium in Nodules
Cells are Fixing atmospheric Nitrogen

28. Residue from legume crops is usually high in N when compared
with residue from other crops and can be a major
source of N for crops that follow legumes in rotation.
Most of the N contained in crop residue is not available to plants
until microbes decompose the plant material.
Residues from legume crops have low carbon to N (C:N) ratios and are easily
decomposed by soil microbes. Residues from non-legume crops
have a higher C:N ratio and are slower to decompose
N Contributions
alfalfa range from 100 to 150 lbN/acre
Soybeans range from lb/acre