NREM 301Forest Ecology & Soils Nutrient Cycling
Day 27November 18, 2008
Uganda Study Abroad Information Meeting5 pm 118 Horticulture - TodayChina - Nov 19 – noon - 9 CurtissMore Info – Ag Study Abroad Office 111 Curtiss
Individual Quiz
Diagram the General Nutrient CycleClearly identify the sub-cycles:
BiochemicalBiogeochemical
Geochemical
Group Activity
Now
Diagram the N CycleIn the
Agricultural landscape of Central IowaInclude each of the words (phrases) on the diagram
1. Decomposition2. Nitrification3. Nitrobactor4. Assimilation5. Ammonification6. Drainage Loss 7. Denitrification8. Nitrogen Fixation9. Anaerobic10. Fertilization
11. Nitrate12. Nitrosomanos13. Ammonia14. Nitrite15. Organic N16. N2 gas17. Mineralization18. Anaerobic19. Tiles20. Surface runoff
Surface Runoff
Fertilization
Group ActivityLeaching & tiles
Be prepared to describe each of the words (phrases) on the diagram
1. Decomposition2. Ammonification3. Nitrification4. Assimilation5. Drainage Loss 6. Denitrification7. Nitrogen Fixation
Are there any processes that are missing – especially in agricultural landscapes?
Nitrogen Cycle
NitrosomonasBacteria
NitrobacterBacteria
Mineralization
Uptake
Let’s look in detail at the N cycle
Anaerobic
Free Living BacteriaSymbiotic N-fixersRhizobiumFrankia
Acid soils – few bacteria & actinomycetes – slower decomposition – most available N for plant uptake is NH4
Basic soils – most diverse – faster decomposition – more NO3 – taken up
Neutral
How does pH influence the Nitrogen Cycle?
What happens to Bacteria at low pH?
Acid
Surface Runoff
Fertilization
Leaching & tiles
Be prepared to describe each of the words (phrases) on the diagram
1. Decomposition2. Ammonification3. Nitrification4. Assimilation5. Drainage Loss 6. Denitrification7. Nitrogen Fixation
Are there any processes that are missing – especially in agricultural landscapes?
Nitrogen Cycle
NitrosomonasBacteria
NitrobacterBacteria
Mineralization
Uptake
Let’s look in detail at the N cycle
Anaerobic
How does soil pH Affect microbial activity
&Nutrient availability?
Many nutrients limited by low pH –some micros - not
High pH also limits availability of some – note especially P and micro-nutrients
Decomposition slowed at low pH –fewer bacteria
Surface Runoff
Fertilization
Group Activity
Uptake
Leaching & tiles
No N from Weathering/All from Atmosphere
Geochemical = 16%
Biogeochemical = 45%
Biochemical = 39%
Identify components of the
sub-cycles as annual sources
What Happens to the N Cycle When -Prairie/forest are replaced by corn and soybeans?
Do the following increase, decrease or stay the same?• Fixation• Plant loss• OM added to soil• Decomposition rate• Ammonification• Nitrification• Denitrification• Leaching• Plant uptake
Surface Runoff
Fertilization
Uptake
Leaching No N from Weathering/All from Atmosphere
What happens to N Cycle when
going from prairie to corn?
• Fixation• Plant loss• OM added to soil• Decomposition rate• Ammonification• Nitrification• Denitrification• Leaching• Plant uptake
downup
downup
upup
Down (tile)
upup
Surface Runoff
No N from Weathering/All from Atmosphere
How does fire impact the N Cycle?
• Plant loss -• OM FF -• Decomposition of left over OM -
• Ash -• pH -• Ammonification –• Nitrification –• Plant uptake –
• Leaching loss –• Fixation -• Denitrification -• Surface runoff –
Up but rapid replacementLost – N volatilized
Increases
Left behind – lots of cationsIncreases – CEC - cations
UpUp especially in conifers
Down – shifts to understory
Up – a short timeUp – symbiotic & free
Up if less TrUp a short time