Using Mineralization Estimates to Predict Nitrogen Fertilizer Needs

1
Using Mineralization Estimates to Predict
Nitrogen Fertilizer Needs N.W. CHRISTENSEN,
R.S. KAROW, D.M. BALOCH, and M.H.
QURESHI Department of Crop and Soil Science,
Oregon State University

• Situation
• Rainfed soft white winter wheat is grown in
  rotation with a number of crops in the Willamette
  Valley of western Oregon.
• Preceding crops affect wheat response to N
  fertilizer in an unpredictable manner.
• Inorganic soil N concentrations fail to predict
  wheat response to spring-applied N.

• Laboratory analyses
• Plant N Leco CNS 2000
• Soil sample 0 to 30 cm, collected in Jan-Feb
• Soil inorganic N NO3-N and NH4-N
• Mineralizable soil N Anaerobic incubation
• ? 20 g soil sample plus 50 mL H20 in 250 mL
  bottle
• ? Incubate air-tight bottle at 40 C for 7 d
• ? Extract with 50 mL 2 M KCl and filter
• ? Analyze for NH4-N
• ? Subtract pre-incubation NH4-N

Results
Grain yield (Mg ha-1)
Available N 5.71Nmin - 50.73 R2 0.78
Crop-available N (kg ha-1)

• Objectives
• Relate field estimates of crop-available N to
  laboratory estimates of soil N mineralization
  potential
• Predict N fertilizer needs using an N budget that
  includes laboratory estimates of nitrogen
  mineralization potential

Grain protein (g kg-1)
Calculations Crop-available N (kg N ha-1)
(plant Nt2 - plant Nt1) (soil Nt2 - soil
Nt1)   where plant N N uptake by unfertilized
control soil N NH4 NO3 to 30 cm t1
Feekes 5 t2 harvest   N fertilizer prediction
(kg N ha-1) 300 (Nmin soil Nt1 plant
Nt1)   where 300 empirical constant Nmin
anaerobic soil test N soil N NH4 NO3 to
30 cm t1 Feekes 5   N rate at Maximum
Economic Yield (kg N ha-1) ((PN/PY)
b1)/2b2   where PN 0.62 kg-1 N ( 0.28
lb-1 N) PY 0.13 kg-1 grain ( 3.60 bu-1)
b1 linear regression coefficient b2
quadratic regression coefficient
Fig. 3. Grain yield and protein at MEY
Nmin soil test (mg N kg-1)

• Conclusions
• Nitrogen available to winter wheat can be
  estimated by measuring mineralizable soil N in
  the laboratory (Fig. 1).
• ? Preceding crops influence crop-available N
• ? Differences exist within and among crops
• Nitrogen fertilizer requirements can be
  calculated from laboratory estimates (Fig. 2).
• ? Mean N fertilizer uptake efficiency at MEY
  0.66
• Yield and protein of soft white winter wheat
  fertilized for MEY fall within acceptable
  ranges (Fig. 3).
• ? Mean yield 8.25 Mg ha-1 range 5.62 to 10.8
• ? Mean protein 92 g kg-1 range 81 to 104 g
  kg-1

Fig. 1. Nmin soil test correlation
MEY N 1.11Rec N 13.10 R2 0.89

• Methods
• Wheat response to N fertilizer
• Field research Nineteen small-plot and on-farm
  trials, 1994 through 1999
• Wheat cultivars Stephens, Gene and Madsen
  
• Soils Argiaquic Xeric Argialbolls, Aquultic
  Argixerolls, Cumulic Ultic Argixerolls,
  and Pachic Ultic Argixerolls
• Preceding crops Clover, corn, grass, and oats
• N rates 0 to 224 kg N ha-1 applied at Feekes 5
• Design RCB with 4 or 5 N rates in 3 or 4
  blocks
• Measured responses Grain yield, grain protein,
  and aboveground N removal regressed on N rate

N fertilizer for MEY (kg ha-1)
Outlier Wheat after clover unresponsive gt56 kg N
ha-1
N fertilizer recommended (kg ha-1)
Fig. 2. N fertilizer prediction