Ammonium Nitrate has Gone Away:
Implications for N Management
Eastern Extension Agent Training,
by Clain Jones, Extension Soil Fertility Specialist
firstname.lastname@example.org; 406 994-6076
• 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.
• Many 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.
- Factors that affect it
- N Source
- The Base Material
Nitric Ammonium Nitrate
Sulfuric Ammonium Sulfate
Carbon Urea (46-0-0)
Urea + A.N. Nitrogen Solution-
+Water UAN (28-0-0, 32-0-0)
• “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
• Exceptions to above rule: N source can
- volatilization if broadcast
- volatilization and availability if coatings or
• Factors affecting?
READY FOR SOME CHEMISTRY??
NH4+ + OH- NH3 (gas) + H2O
• Not an issue if fertilizer is incorporated at
least 1.5 inches into soil-not an option with
established forages or no-till.
• 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
N fertilizer can increase pH during ‘hydrolysis’
Ex: Urea enzyme
CO(NH2)2 + 2H2O 2NH4+ + CO32-
CO32- + H2O HCO3- + OH-
Effect on pH? Increases temporarily. Why?
Good or bad? Bad: pH, volatilization
(NH4+ + OH- NH3 (gas) + H2O)
Ammonium nitrate (AN) has little effect on soil pH,
therefore generally does not volatilize much.
Ammonium sulfate (AS) shouldn’t raise pH much
on non-calcareous soils (but it’s expensive).
Ammonia Volatilization Losses from a
Ammonia Loss (%)
Ammonium Ammonium Nitrate Urea
Sulfate Gesgin and Bayarakll, 1995
Why differences in volatilization?
• Urea and AS cause larger pH increases than
• ½ of N in AN is nitrate which can’t volatilize
• Why does AS volatilize more on calcareous
Sulfate dissolves some CaCO3, pH
Factors Affecting Volatilization
• High soil pH
• Low Cation Exchange Capacity (CEC)-why?
• Moist soil/humid conditions
• 0.1 in. of rain dissolves fertilizer, allows
• 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.
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
Effect of N Rate and Source
70% Orchardgrass/30% Alfalfa, W. Montana
Averages of 2 sites
0 40 80 120
Economics? N rate (lb/ac)
Christiansen, unpub. data
Effect of N Source on Irrigated W. Wheatgrass Yield
Averaged over 4 N Rates, Blaine County
Christiansen, unpub. data
AN UR AS
Still, need to apply when cool, calm or some ammonia
will volatilize, especially from UR and AS.
Effect of N Source on Winter Wheat Grain Yield
North Central MT
Christensen and Meints. Agron J. 74:840-844.
34-0-0 Average of two application dates (November and March)
Grain Yield (bu/acre)
0 30 60 90
No significant N
Broadcast N (lb/acre) source effects
How could UR produce similar yields as AN if
UR volatilizes more?
1. AN leaches more readily
2. Takes less energy for plant to convert
ammonium-N than nitrate-N to protein.
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
-can more easily top-dress if have
-some N can be absorbed through leaves?
- mainly cost
- volatilization can be higher than granular
• 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 published studies. 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.,
Use? Would need to compare Agrotain cost with urea cost,
and consider potential for volatilization, including
- Surface broadcast. Best chance for volatilization.
Established forage, essentially only option.
- Seed-placed: Dry grains-can dramatically
decrease emergence. MSU recommends less than
10-20 lb N/ac be applied directly with seed
depending on crop, with 0-10 lb N/ac for urea.
Increasing spreader width can help (see next slide)
• Liquid (UAN; 32-0-0 or 28-0-0): Surface
broadcast (including fertigation), surface
band, or knifed.
Method Forage Yield
Surface Broadcast 2.9 t/ac
Surface Band 3.4 t/ac
N. Central Regional
WHY? Extension Pub #326, KSU
Hypothesized to be due to limited urease
concentration, slowing hydrolysis
• 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 if > ~ 20 lb N/ac (crop
dependent). Yield losses at higher rates
(40-60 lb N/ac).
•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
on hay fields.
• 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
1. Ex: Shallow, coarse soil. Fall or Spring? Spring
2. Ex: Cool Fall temps with ability to irrigate, or
warmer spring temps before irrigation water
delivered. Fall or Spring?
• 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 doesn’t
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 (>0.5”).
For more information on urea volatilization and
For more information on N cycling, fertilizer sources,
placement and timing see Nutrient Mgmt Modules:
MSU Soil Fertility webpage: