Ammonia Volatilization Grains and Forages

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					Ammonium Nitrate has Gone Away:
 Implications for N Management

  Eastern Extension Agent Training,
               2005
by Clain Jones, Extension Soil Fertility Specialist
      clainj@montana.edu; 406 994-6076
               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.
• 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.
            Presentation Outline
• Volatilization
  - Mechanism
  - Amounts
  - Factors that affect it

• Management
  - N Source
  - Placement
  - Timing
 Anhydrous Ammonia
  - The Base Material

         Nitric     Ammonium Nitrate
         Acid       (34-0-0)
       Sulfuric     Ammonium Sulfate
        Acid        (21-0-0-16)

NH3   Phosphoric
         Acid
                    Ammonium Phosphate
                    (11-52-0, 18-46-0)
        Carbon      Urea (46-0-0)
        Dioxide

      Urea + A.N.   Nitrogen Solution-
        +Water      UAN (28-0-0, 32-0-0)
                   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 can
  affect
 - volatilization if broadcast
 - volatilization and availability if coatings or
 inhibitors
      Ammonia Volatilization
• Mechanism?
• Amounts?
• Factors affecting?




READY FOR SOME CHEMISTRY??
            Ammonia Volatilization

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’
                       Urease
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
                                 Calcareous Soil
                   16
                   14
Ammonia Loss (%)




                   12
                   10
                    8
                    6
                    4
                    2
                    0
                         Ammonium    Ammonium Nitrate           Urea
                          Sulfate                  Gesgin and Bayarakll, 1995
  Why differences in volatilization?
• Urea and AS cause larger pH increases than
  AN.
• ½ of N in AN is nitrate which can’t volatilize
• Why does AS volatilize more on calcareous
  soils?

   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
  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.
QUESTIONS?
N Management
 -N Source
 -Placement
 -Timing
            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
               7.5


               7.0
                                          UR                               AN
Yield (t/ac)




               6.5


               6.0


               5.5
                                                           Averages of 2 sites

               5.0
                     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
               3.6
                                                              Christiansen, unpub. data

               3.4
               3.2
Yield (t/ac)




                3
               2.8
               2.6
               2.4
               2.2
                2
                             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.
                        65
                        60   46-0-0
                             34-0-0      Average of two application dates (November and March)
Grain Yield (bu/acre)




                        55
                        50
                        45
                        40
                        35
                        30
                        25
                        20
                               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
           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
              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 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.,
  1991).
Use? Would need to compare Agrotain cost with urea cost,
  and consider potential for volatilization, including
  weather.
QUESTIONS?
                 Placement
• Granular
  - 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)
          Placement (Cont’d)
• 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
          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 if > ~ 20 lb N/ac (crop
  dependent). Yield losses at higher rates
  (40-60 lb N/ac).
                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
on hay fields.
            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?      Spring
2. Ex: Cool Fall temps with ability to irrigate, or
  warmer spring temps before irrigation water
  delivered. Fall or Spring?
                                    Fall
                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 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”).
          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 Nutrient Mgmt Modules:
http://landresources.montana.edu/nm
MSU Soil Fertility webpage:
http://landresources.montana.edu/soilfertility

				
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