Nitrogen sources for Topdressing

1
Nitrogen sources for Topdressing
Using Variable Nitrogen Fertilizers
2
Why are we worried about managing Nitrogen
inputs?
There not worried about Nitrogen!
3

• What forms of N are we using
• What are the safest as far as N loss
• What forms are most economical
• All these are factors in the decision making
  process for good reasons
• Urea 46-0-0
• UAN 28 /32
• Ammonium nitrate 33-0-0

4
Urea 46-0-0

• It is no surprise that Urea is widely used here
  either because
• Available everywhere
• Easy to handle
• Not nearly as dangerous as AA
• Urea is the most widely used solid fertilizer N
  source in the world 23,610,991 Mt used for
  cereal production in 1998 (www.FAO.org).
• How is N from Urea lost?
• Volatilization losses from surface applications
  of urea-based fertilizers are thought to occur in
  sizeable quantities (Ernst and Massey, 1960 Fenn
  and Hossner, 1985).

5
Protecting Urea Investments
Urea fertilizers must be hydrolyzed by the
enzyme urease before urea-N becomes plant
available. This of course takes time Increases
in urease activity can result in more N loss due
to volatilization. Urease activity is moisture
and temperature dependent.
6
Conditions that favor N loss

• Wind
• Increases evaporation
• Soil pH exceeding 7.0
• Soil Temp exceeding 50F
• For Urea, sandy soils with low organic matter
  will likely favor N loss
• Volk (1966) stated that after applying urea not
  incorporated, 14 days later 80 of N applied was
  gone.

7
Avoiding loss of N

• For urea, apply before an expecting rainfall
  event. (½ in rain is adequate.
• Try to apply on a calm and cool day. (Unlikely in
  western Oklahoma)
• Do not apply Urea on a soil that is damp.
• Even a slight dew in the mornings can cause
  significant volatilization.
• Rainfall or irrigation can result in subsurface
  incorporation thus minimizing volatilization
  losses.
• Significant precipitation (gt.25 cm) 3 to 6 d
  after application can efficiently reduce
  volatilization losses (Havlin et al., 1999).

8
Higher risk conditions Lower risk conditions
High soil temperature (gt70oF) Low soil temperature (lt50oF)
Moist soil or heavy dew Dry soil
High soil pH (gt7.0) Low soil pH (lt6.0)
Low cation exchange Capacity soil (sandy) High cation exchange capacity soil (silt or clay-dominated)
Crop residue, perennial forage, or ash layer from recent burn event Urease Inhibitor

9
Volatilization
10
UAN (28, 32-0-0)

• Advantages
• Generally available fertilizer
• Not as susceptible to N loss as Urea
• Can be used as a carrier for herbicides
• Contains both Nitrate and Urea, spreads out risk
  

• Disadvantages
• Can cause leaf burn
• Generally more expensive than Urea or Anhydrous
  Ammonia
• UAN, is still 50 urea so can be somewhat
  susceptible to volatilization

11
Avoiding Burn do to Fertilization

• Avoid application during high wind speed to
  reduce burn and volatilization
• Avoid application on a warm day. (A guy who
  applied a heavy dose on a 75 degree day lost that
  whole field)
• Use streamer nozzles for improved soil contact
  and penetration
• Avoid application when temps exceed 60F

Many times even a moderate burn from UAN has no
detrimental yield hit
12
Urease Inhibitors

Table 1. Mean yields for urease (NBPT) inhibitor trials conducted in 1989 at the Purdue Agronomy Farm, SEPAC, Pinney Purdue, and the Kosciusko location. Table 1. Mean yields for urease (NBPT) inhibitor trials conducted in 1989 at the Purdue Agronomy Farm, SEPAC, Pinney Purdue, and the Kosciusko location.
Fertilizer Treatment Yield (bu/acre)
Control (20 lb N/acre in starter only) 99
Urea broadcast on the surface 130
Urea NBPT broadcast on the surface 143
UAN broadcast on the surface 135
UAN NBPT broadcast on the surface 140
UAN dribbled on the surface 139
UAN point (spoke) injected 142
UAN coulter injected 147
UAN knife injected 145
Urease inhibitor N (n-butyl) thiophosphoric triamide Urease inhibitor N (n-butyl) thiophosphoric triamide
Source Phillips, Mengel, and Walker, Purdue University Source Phillips, Mengel, and Walker, Purdue University
13
References Questions
Nitrogen Loss from Urea Fertilizer Applications
on Hot, Dry, Soils, R.W. Mullen, G.V. Johnson,
K.W.Freeman,K.J. Wynn, W.E. Thomason, and W.R.
Raun Management of Urea Fertilizers, Montans
State University Extension Publication, Paul V.
Dixon, Soil and Fertilizer N, Chapter 5 Lecture
Soil Nutrient Management, W.R. Raun