Nitrogen Use Efficiency as Influenced by Crop Response Index.

1
Nitrogen Use Efficiency as Influenced by Crop
Response Index.

• G.V. Johnson, W.R. Raun, R.W. Mullen, R.L.
  Westerman and B.B. Tucker
• Department of Plant and Soil Sciences
• Oklahoma State University
• R.A. Olson
• Department of Agronomy
• University of Nebraska

2
Response Index
Potential for increased yield
Higher NUE LowerNUE
Apply more N Apply less N
RI gt 1.5 RI lt 1.5
3
Improving Nitrogen Use Efficiency for Cereal
Production

• Raun and Johnson. 1999. Agron. J. 91357-363.
• Worldwide NUE 33
• 1 change 234,658, 462

4
Improving Nitrogen Use Efficiency for Cereal
Production

• Potential Improvements
• Crop Rotations
• Forage Production Systems
• Hybrid or Cultivar
• Conservation Tillage
• NH4-N Source
• In-Season and Foliar-Applied N
• Fertigation
• High Resolution Precision Management

5
Improving Nitrogen Use Efficiency for Cereal
Production

• Cause of low NUE
• Soil-Plant system leaks
• Loss increases with excess mineral-N

6
Loss of N from soil-plant system
7
Harvested-N1 - Harvested-N0
NUE
X 100
Fertilizer-N1
8
Influence of year on NUE winter wheat receiving
90 kg N/ha.
9

• Unfertilized yield is variable over time.

Control plot yield of winter wheat (Lahoma, OK)
y -15.78x 1910 C.V. 30.4
1974
745
10

• Fertilized yield is variable over time.

Maximum yield of winter wheat (Lahoma, OK)
Y 23.95x 2581 C.V. 20.5
3045
3088
11
Are fertilized and unfertilized wheat yields
related?
12
What is the temporal variability of fertilizer-N
response?

• Response Index (RI)
• RI Max yield Nx / yield N0
• RI Indication of the degree to which N,
  external to the growing environment, is needed to
  support potential yield.

13
Temporal variability of wheat response to N
14
Relationship of fertilized and non fertilized
yield to R.I.
15
Irrigated maize and sorghum
16
Response Index for irrigated maize and sorghum
over time.
17
Conclusions

• NUE of wheat is usually lt 70 at low
  fertilizer-N rates and decreases with increasing
  N input.
• NUE for maize and sorghum is usually lt 50 .
• Supply of non-fertilizer N to crop changes
  greatly from year to year.
• Soil moisture and temperature variability?

18
Conclusions

• Response to fertilizer-N is influenced more by
  external N inputs and mineralized soil-N (N0
  yield) than by potential yield, in a given year.
• Since this is found for soil that has not
  received fertilizer N for over 20 year, it is
  even more likely to occur in fields that have a
  history of receiving fertilizer-N each year.

19
Conclusions

• NUE may be improved by knowing the response
  index and avoiding excess fertilizer-N.
• Identify potential yield each year.
• Identify non-fertilizer N contributions.
• Apply fertilizer-N in-season.