Nitrogen Loss from Urea Fertilizer Applications on Hot, Dry Soils

1
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

Oklahoma State University Department of Plant and
Soil Sciences
2
Introduction

• 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).
• Volatilization losses from surface applications
  of urea-based fertilizers are thought to occur in
  sizeable quantities (Ernst and Massey, 1960 Fenn
  and Hossner, 1985).

3
Introduction

• Urea fertilizers must be hydrolyzed by the enzyme
  urease before urea-N becomes plant available.
• Increases in urease activity can result in more N
  loss due to volatilization.
• Urease activity is moisture and temperature
  dependent.

4
Introduction

• Urea hydrolysis is maximized when moisture levels
  are optimum for plant growth (Havlin et al.,
  1999).
• Volk (1966) reported that 14 d after application
  of prilled urea to air-dry soil 80 had not been
  hydrolyzed.
• McInnes et al. (1986) found hydrolysis was
  minimal following urea application to dry soil,
  but following wetting, urea hydrolysis increased.

5
Introduction

• Urease activity has been observed from 2ºC to
  37ºC (Havlin et al., 1999).
• Urease activity is positively correlated with
  temperature (Clay et al., 1990)
• Fisher and Parks (1958) found that hydrolysis was
  50 and 85 complete at temperatures 10 and 20ºC,
  respectively, two weeks after urea application.

6
Introduction

• Mechanical incorporation of urea fertilizers can
  effectively decrease N-loss due to
  volatilization.
• Increased soil surface area to absorb released
  NH3 (Havlin et al., 1999).
• Palma et al. (1998) reported N-loss decreased
  from 8.6 to 5.4 when urea was incorporated.

7
Introduction

• 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
Objectives

• To determine decreases in winter wheat yield
  which could be attributed directly to N-loss via
  volatilization.
• To determine the effect of surface application or
  incorporation on winter wheat N uptake.

9
Materials and Methods

• Two experimental sites
• Stillwater and Tipton, OK
• Experimental design RCBD
• Eight treatments with three replications
• Three N sources both surface applied and
  incorporated and one injected source
• Urea (46-0-0), Urea ammonium nitrate (AN
  28-0-0), and ammonium nitrate (AN 34-0-0)
• AA (82-0-0)

10
Materials and Methods

• All N was applied at a 112 kg N ha-1 rate.
• Urea and AN were applied using conventional
  dry-fertilizer spreader.
• UAN was broadcast applied using spray applicator.
• AA was injected 15 cm below soil surface using
  custom built applicator.
• Incorporated treatments received a 15-cm tillage
  pass.

11
Materials and Methods

• Winter wheat variety Jagger planted in 21-cm
  rows at a rate of 88 kg ha-1.
• Harvested area 2.0 x 6.1 m.
• Grain sample taken from each plot for N analysis
  using Carlo-Erba dry combustion analyzer
  (Schepers et al., 1989)

12
Results and Discussion

• 1998-1999 Yield response at Stillwater

13
Results and Discussion

• 1998-1999 N uptake at Stillwater

14
Results and Discussion

• 1998-1999 Yield response at Tipton

15
Results and Discussion

• 1998-1999 N uptake at Tipton

16
Results and Discussion

• 1999-2000 Yield response at Stillwater

17
Results and Discussion

• 1999-2000 N uptake at Stillwater

18
Results and Discussion

• 1999-2000 Yield response at Tipton

19
Results and Discussion

• 1999-2000 N uptake at Tipton

20
Conclusions

• Incorporation of urea fertilizers tended to
  increase yields when compared to surface
  applications.
• Losses due to volatilization may have been
  depressed due to rainfall within a week of
  fertilizer application in both years.