or phosphorous

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or phosphorous?
Phosphorus
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P has one stable isotope, 31P
and one important radioactive isotope, 32P
32P labeling can be used to track the fate of
added P but its use is limited by its short half
life (14.3 days)
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Phosphorus Chemistry
Most common inorganic forms HPO4-2 and
H2PO4-1
Unlike N, P does not readily change oxidation
states
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• No major gaseous forms
• unlike C, N, and S
• Movement of P from terrestrial to aquatic systems
  is very important ecologically
• Humans have greatly altered P cycling
• Mining, application of P fertilizers, manure
  management, accelerated erosion

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P in Plant Nutrition

• Essential to plants and animals
• ATP, DNA, RNA, phospholipid membranes
• Critical to energy flow in cells
• Usually 0.2 to 0.4 of dry matter
• Mycorrhizae strongly influence P uptake by most
  plants

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P and Soil Fertility

• Naturally most soils contain low levels of total
  P (typically 1/10 to 1/4 as much as N)
• Most of the P in soil is not available to plants
• Soluble P added to soils can be fixed by
  reaction with Fe and Al in acid soils and Ca and
  Mg in alkaline soils.

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Normal (left) and phosphorus-deficient (right)
corn plants. Note stunting and purple color
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P Sorption

• Adsorption-desorption reactions strongly regulate
  P availability in soils
• PO43- gt SO42- gtgt Cl- gt NO3-
• In most soils, solution concentrations of P are
  kept low by adsorption reactions, minimizing
  losses of P through leaching.

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Ortho- phosphate
The dominant form of ortho-phosphate found in
soil varies with pH
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Polyphosphates
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Sub-soil P availability in Illinois
3 regions have been identified that tend to
differ in their natural ability to supply crops
with P. Parent material, degree of weathering,
native vegetation, and natural drainage vary
within the regions causing within region
variation in P availability. It appears for
example that that soils that developed under
forest cover have more available subsoil P than
those developed under grass.
The high P region is in western Illinois. These
soils formed on gt 4 feet of loess with relatively
high P content. The soils are leached of
carbonates to a depth of more than 3 1/2 feet,
and roots extend deeply in the moderately
permeable profiles.
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Sub-soil P availability in Illinois
The medium P region is in central Illinois,
with arms extending into northern and southern
Illinois. These soils formed on shallower layers
of loess over glacial till, glacial drift, or
outwash. These soils are more likely to be poorly
drained and have shallow carbonate accumulations
than in the high region. The soils in the
northern and central areas are generally free of
root restrictions, whereas soils in the southern
arm are more likely to have root-restricting
layers. Much of the variation in availability
of P within this region is related to natural
drainage patterns. Soils with good internal
drainage tend to have higher levels of available
P whereas soils with poor internal drainage have
lower levels of available P.
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Sub-soil P availability in Illinois
In the low P region in southeastern Illinois,
the soils were formed from 2 1/2 to 7 feet of
loess over weathered Illinoisan till. The
profiles are more highly weathered than in the
other regions and are slowly or very slowly
permeable. Root development is more restricted
than in the high or medium regions. Subsoil P
levels may testhigh in some soils of the
region, but this is offset by conditions that
restrict rooting. In the low region in
northeastern Illinois, the soils were formed from
thin loess (less than 3 feet) over glacial till.
Glacial till is generally low in available P. In
addition, shallow carbonates are common as are
subsoil conditions (e.g., high bulk density and
slow permeability) that restrict root development.
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• Low uptake of P from the subsoil is normally
  related to one or more of the following factors
• 1. A low supply of available P in the sub-soil
  because (a) the parent material was low in P (b)
  P was lost in the soil forming process or (c)
  the P is made unavailable by calcareous material.
• 2. Poor internal drainage that restricts root
  growth.
• 3. A dense, compact layer that inhibits root
  penetration or
• branching.
• 4. Shallowness to bedrock, sand, or gravel.
• 5. Droughtiness, strong acidity, or other
  conditions that restrict
• crop growth and reduce rooting depth.

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Relationship between extractable P and crop yield
Build up and maintenance
Maintenance
No added P
Low Medium High
Extremely high
Response to fertilizer is likely
Response to fertilizer is unlikely
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Soil test calibration
Response curves are fit to data from field
experiments
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Corn yield response to P1
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in 4 years
General rule of thumb 9 lbs of P2O5 are
required to raise P1 by 1 lb
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Maintenance rates of P2O5
and K2O for various crops
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Draw down of extractable P in the absence of
fertilization
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Can anyone remember the relationship between
elemental P and P2O5 ?
1 lb of elemental P 2.29 lbs of P2O5
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Sowhy do we talk about P2O5 when plants dont
take up P2O5 and none of our phosphorus
fertilizers actually contain P2O5 ?
Tradition !
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Draw down of extractable P in the absence of
fertilization
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P Fertilizer Inputs to Illinois
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P Balance, Manure, and Sewage Effluent
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Illinois P Mass Balance1979 to 1998
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Animal Product
Grain
Animal
Net grain export
155
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Fertilizer
Net 27
122
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173
6.6
Sewage
Human
Riverine Export
(1000 tons P yr-1)
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Sewage Effluent Estimates

• 47 of total P in IL rivers
• 70 for Illinois River, 33 for others in state

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ADDs

• Automatic dishwasher detergents
• 3 to 8 P
• Nearly all have P
• MWRDGC efforts
• House Bill 1502, 10 February 2005 (also senate)
• Soap and Detergent Association

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Many soils have high levels of soil test P
because of historically high rates of P
(relative to crop removal).
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Phosphorus fertilizers
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Manures and Composts as P Sources

• Majority of P in manures and composts is
  inorganic P

Source Eghball et al., 2002. J. Soil Water
Conserv. 57470-473.
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Summary of P management concepts

• Extensive root growth is important, since P moves
  very slowly in most soils
• Banding reduces P fixation
• Seedlings provided with high P develop greater
  yield potential
• Uptake of P continues throughout the season
• Corn response to P is normally related to soil
  test P
• Adequate P fertility is key to efficient use of N
  and other nutrients

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Myth 1 Phosphorus does not move through soil.
While most P losses occur with surface runoff,
P may move through soils with combinations of low
P-fixing capacities, with preferential flow (or
subsurface drains), or high soil test P contents.

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Myth 2 Soils are infinite sinks for P.
Research shows that soils cannot indefinitely
fix applied P. Continued applications of P beyond
crop requirements, a common scenario where
organic wastes have been heavily used in
agriculture, are a major cause of soil P
saturation.
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Myth 3 Erosion control will stop P losses in
runoff. Erosion control is not the sole answer
reduction of dissolved P loss in runoff can only
be achieved by minimizing P loss at the source
and implementing practices that reduce total P in
runoff. By controlling point sources we can solve
water quality problems. Although point source
inputs have been reduced in many areas, nonpoint
source inputs now contribute to a greater share
of water quality problems.
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Myth 4 Crop N requirements should drive manure
management. Basing manure management on mature
N and crop N needs can lead to undesirably high P
applications due to the unfavorable NP ratios of
most manures and crop requirements.
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Myth 5 Phosphorus management strategies can be
universally applied. All fields and water
bodies are not created equal management plans
for P and best management practices must be
tailored to site vulnerability to P loss and
proximity of P-sensitive waters.
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Myth 6 We don't know enough about P to
implement sound environmental recommendations.
We know a lot about how P reacts with soil and
is transferred to runoff, but we have not
adequately disseminated this information to land
users and state and federal agencies.