NREM 301
Forest Ecology & Soils
Nutrient Cycling
Day 27
November 18, 2008
Uganda Study Abroad Information Meeting
5 pm 118 Horticulture - Today
China - Nov 19 – noon - 9 Curtiss
More Info – Ag Study Abroad Office 111 Curtiss
Individual Quiz
Diagram the General Nutrient Cycle
Clearly identify the sub-cycles:
Biochemical
Biogeochemical
Geochemical
Biochemical
General Nutrient
Cycle
Geochemical
Biogeochemical
Group Activity
Now
Diagram the N Cycle
In the
Agricultural landscape of Central Iowa
Include each of the
words (phrases) on the
diagram
1. Decomposition
2. Nitrification
3. Nitrobactor
4. Assimilation
5. Ammonification
6. Drainage Loss
7. Denitrification
8. Nitrogen Fixation
9. Anaerobic
10. Fertilization
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
Nitrate
Nitrosomanos
Ammonia
Nitrite
Organic N
N2 gas
Mineralization
Anaerobic
Tiles
Surface runoff
Nitrogen Cycle
Fertilization
Let’s look in detail at
the N cycle
Free Living Bacteria
Symbiotic N-fixers
Rhizobium
Frankia
Be prepared to describe
each of the words
(phrases) on the diagram
Surface
Runoff
Anaerobic
Uptake
Leaching & tiles
Decomposition
Ammonification
Nitrification
Assimilation
Drainage Loss
Denitrification
Nitrogen Fixation
Are there any processes that
are missing – especially in
agricultural landscapes?
Nitrobacter
Bacteria
Nitrosomonas
Bacteria
1.
2.
3.
4.
5.
6.
7.
Group Activity
Mineralization
How does pH
influence the
Nitrogen Cycle?
What happens to
Bacteria at low pH?
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
Acid
Neutral
Nitrogen Cycle
Let’s look in detail at
the N cycle
Fertilization
Be prepared to describe
each of the words
(phrases) on the diagram
Surface
Runoff
Anaerobic
Uptake
Leaching & tiles
Decomposition
Ammonification
Nitrification
Assimilation
Drainage Loss
Denitrification
Nitrogen Fixation
Are there any processes that
are missing – especially in
agricultural landscapes?
Nitrobacter
Bacteria
Nitrosomonas
Bacteria
1.
2.
3.
4.
5.
6.
7.
Mineralization
How does soil pH
Affect microbial activity
&
Nutrient availability?
Decomposition
slowed at low pH –
fewer bacteria
High pH also limits
availability of
some – note
especially P and
micro-nutrients
Many nutrients
limited by low pH –
some micros - not
No N from Weathering/All
from Atmosphere
Fertilization
Geochemical = 16%
Biogeochemical = 45%
Surface
Runoff
Uptake
Leaching & tiles
Biochemical = 39%
Identify
components of the
sub-cycles
as annual sources
Group Activity
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
What happens to N
Cycle when
going from prairie to
corn?
Fertilization
Surface
Runoff
• Fixation down
• Plant loss up
• OM added to soil down
• Decomposition rate up
• Ammonification up
• Nitrification up
• Denitrification Down (tile)
Uptake
Leaching
• Leaching up
• Plant uptake up
No N from Weathering/All from Atmosphere
What Happens to N Cycle When Land is Drained?
Results of Drainage
Nitrate Loads to Mississippi River
How does fire impact the N
Cycle?
• Plant loss - Up but rapid replacement
• OM FF - Lost – N volatilized
• Decomposition of left over OM Increases
Surface
Runoff
• Ash - Left behind – lots of cations
• pH - Increases – CEC - cations
• Ammonification – Up
• Nitrification – Up especially in conifers
• Plant uptake – Down – shifts to
understory
• Leaching loss – Up – a short time
• Fixation - Up – symbiotic & free
No N from Weathering/All from
Atmosphere
• Denitrification - Up if less Tr
• Surface runoff – Up a short time
How does the Phosphorus Cycle differ from the N Cycle?
Detergents
Includes animal waste
Not much
atmospheric input
Major Loss
Mining Phosphate Rocks
Minor compared to
N