Ammonium Nitrate has Gone Away: Implications for N Management of Forages

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Ammonium Nitrate has Gone Away Implications for
N Management of Forages Western Extension Agent
Training, 2005
by Clain Jones, Extension Soil Fertility
Specialistclainj_at_montana.edu 406 994-6076
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Why Important?

• Of all the nutrients, N generally has the largest
  effect on yield and quality.
• Ammonium nitrate (34-0-0) has been discontinued
  by both Simplot and Agrium, affecting N source
  options for many growers.
• Forage producers have historically used ammonium
  nitrate partially due to concerns with
  volatilization of alternatives, such as urea
  (46-0-0), and now will need information from you
  on alternatives.

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Presentation Outline

• Volatilization
• - Mechanism
• - Amounts
• - Factors that affect it
• Management
• - N Source
• - Placement
• - Timing

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Anhydrous Ammonia - The Base Material
Nitric Acid
Ammonium Nitrate (34-0-0)
Sulfuric Acid
Ammonium Sulfate (21-0-0-16)
NH3
Phosphoric Acid
Ammonium Phosphate (11-52-0, 18-46-0)
Carbon Dioxide
Urea (46-0-0)
Urea A.N. Water
Nitrogen Solution-UAN (28-0-0, 32-0-0)
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N Source

• A pound of N is a pound of N-cost per unit of N
  and available equipment to apply N are likely 2
  most important factors in selecting N. Beware
  those who say differently.
• Exceptions to above rule N source affects
• - volatilization if broadcast
• - volatilization and availability if coatings or
  inhibitors

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Ammonia Volatilization

• Mechanism?
• Amounts?
• Factors affecting?

READY FOR SOME CHEMISTRY??
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Ammonia Volatilization

• Not an issue if fertilizer is incorporated at
  least 1.5 inches into soil-not an option with
  established forages
• Losses vary with environment and are
  difficult to predict. Most research done in
  Kansas and Texas where climate is more conducive
  to volatilization.

Looking at above equation, what is 1 factor that
increases volatilization?
High pH
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N fertilizer can increase pH during hydrolysis
Urease enzyme
Ex Urea
CO(NH2)2 2H2O 2NH4 CO32-
CO32- H2O HCO3- OH- Effect on pH?
Increases temporarily. Why?
Good or bad?
Ammonium nitrate (AN) has little effect on soil
pH, therefore generally does not volatilize much.
Ammonium sulfate (AS) shouldnt raise pH much on
non-calcareous soils (but its expensive).
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Why differences in volatilization?

• Urea and AS cause larger pH increases than AN.
• ½ of N in AN is nitrate which cant volatilize
• Why does AS volatilize more on calcareous soils?

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• Ammonium sulfate volatilization process

NOTE Generation of OH-, so pH rises. In words
Sulfate dissolves some calcium carbonate
releasing carbonate which increases pH. Increased
pH increases volatilization. Note Ca-nitrate is
too soluble to form so AN doesnt dissolve CaCO3.
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Factors Affecting Volatilization

• High soil pH
• Low Cation Exchange Capacity (CEC)-why?
• Moist soil/humid conditions
• 0.1 in. of rain dissolves fertilizer, allows
  volatilization
• 0.5 in. of rain/irrigation pushes dissolved
  fertilizer about 2 in. into soil, minimizing
  volatilization if within about 2 days of
  fertilization
• High temperature, wind
• Ground cover/vegetation/residue. WHY?
• Soluble and Exchangeable Ca (decreases)

Bottom line Large number of factors make
volatilization amounts VARIABLE and difficult to
predict.
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How can Ca2 decrease volatilization?
CO(NH2)2 2H2O Ca2-soil 2NH4-soil
CaCO3 In words Calcium can tie up a carbonate
ion, preventing pH rise AND opening up 2 exchange
sites for ammonium.
NOTE No generation of OH-, so no pH rise.
Implication Less concern with volatilization on
soils with high exchangeable Ca levels (generally
indicated by high CEC). Does not matter though if
urea doesnt reach soil.
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Is volatilized NH3 all lost?

• No.
• 7 15 of volatilized urea was found to be
  reabsorbed by hard red spring wheat fertilized 2
  to 3 months after seeding (Ping et al., 2000)

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QUESTIONS?
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N Management
-N Source -Placement-Timing
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Granular N Sources Effect on Yield-Montana
Research Results
Note No journal-published data in Montana on
effect of N source on volatilization and only one
known published study on yield
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Economics?
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Still, need to apply when cool, calm or some
ammonia will volatilize, especially from UR and
AS.
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Summary Urea volatilization can happen, but in
Montana studies it generally did not have a
significant effect on yield compared to other
granular N fertilizers
How could UR produce similar yields as AN if UR
volatilizes more?

• AN leaches more readily
• Takes less energy for plant to convert ammonium-N
  than nitrate-N to protein.

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Liquid Fertilizers

• Advantages
• -can more easily top-dress if have equipment
• -some N can be absorbed through leaves?
• Disadvantage
• - mainly cost
• - volatilization can be higher than granular

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Urease Inhibitors

• Agrotain (NBPT) is main product. Delays
  hydrolysis by up to 14 days
• -advantage allows more chance for rain or
  irrigation to push N into ground
• -disadvantage will delay time to become
  available, volatilization can still occur, and
  cost (adds 50/t-urea).
• Research Results Few studies on forages. One
  showed NBPT significantly reduced ammonia
  volatilization (Watson, C.J. et al., 1994) on
  grassland and one showed Kentucky bluegrass yield
  increased 15 (Joo et al., 1991).
• Use? Would need to compare Agrotain cost with
  urea cost, and consider potential for
  volatilization, including weather.

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QUESTIONS?
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Placement

• Granular On established forage, surface
  broadcast is essentially only option. Others?
• Liquid (UAN 32-0-0 or 28-0-0) Surface broadcast
  including fertigation, surface band, or knifed.
• Method Forage Yield
• Broadcast 2.9 t/ac
• Knife 2.8 t/ac
• Surface Band 3.4 t/ac
• WHY?

N. Central Regional Extension Pub 326, KSU
Hypothesized to be due to limited urease
concentration, slowing hydrolysis
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Foliar Application

• Some N can be absorbed through leaves
• However, most foliar applied N ends up being
  washed off and taken up by roots
• -Only 8-11 of foliar applied liquid urea was
  taken up by leaves, whereas 37-67 of
  soil-applied N was taken up by plant in same
  study (Rawluk et al., 2000).
• Risk of burn? Likely not an issue due to low
  rates applied (25 lb N/t). Has anyone heard of
  grass burn?

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Timing

• Yield and quality are affected by timing
• Because UR may take days to weeks to hydrolyze,
  UR should be applied earlier than AN historically
  was for fast green-up (AN simply dissolves, UR
  requires reaction to be catalyzed by urease).

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Timing, continued

• Fall vs Spring
• Generally better to apply near peak uptake to
  avoid losses (volatilization, denitrification,
  leaching, immobilization). However, weather
  conditions (temp., precip.) in first few days
  after application combined with soil texture may
  be more important.
• 1. Ex Shallow, coarse soil. Fall or Spring?
• 2. Ex Cool Fall temps with ability to irrigate,
  or warmer spring temps before irrigation water
  delivered. Fall or Spring?

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Conclusions

• Urea has become the primary N granular option, so
  Extension agents will likely be getting more
  questions on its use.
• Urea volatilization can happen but doesnt appear
  to have large effects on crop yield in Montana.
  Effects can be reduced with well thought out
  placement and timing.
• Urea should be applied during cool, calm periods
  prior to irrigation or rain event (gt0.5).

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QUESTIONS?
For more information on urea volatilization and
management, see http//www.oznet.ksu.edu/library/
crpsl2/NCR326.pdf For more information on N
cycling, fertilizer sources, placement and timing
see http//landresources.montana.edu/nm MSU
Soil Fertility webpage http//landresources.monta
na.edu/soilfertility