1. Reducing N fertilizer field losses by managing spatial and temporal response variability
G. V. Johnson and W. R. Raun
Dept. Plant & Soil Sciences
Oklahoma State University
Stillwater, OK

2. The Problem: Poor NUE Worldwide NUE in cereals  33%
1 % improvement  490,000 Mg/yr
1 % improvement  $235,000,000/yr.
Higher NUE = lower field N losses

3. Poor NUE

4. Poor NUE

5. Poor NUE Fertilizer Volatilization H+ + NO3- O2 + CEC (-) NH4+
Source and fate of ammonium (NH4+).
Volatilization
Fertilizer
H+ +
NO3-
O2 +
CEC (-)
NH4+
Soil Organic
Matter-N
Mineralization +
OH-
NH3 + H2O

6. Poor NUE Rainfall Denitrification Fertilizer Leaching Nitrification
Source and fate of nitrate (NO3-).
NO3-
Denitrification
N2O and N2
- O2
Rainfall
NO3-
Fertilizer
O2 + NH4+
Nitrification
H+ +
Leaching
NO3-

7. Poor NUE

8. Poor NUE
Result of mineral N present at concentrations in excess of plant needs.

9. Crop N Need Growth Stages in Cereals Heading Stem Extension Tillering
Ripening
Stage
Heading
Stem Extension
Growth Stages in Cereals
Crop N Need
Tillering

10. Temporal variability
Uncertain yield potential

11. Temporal variability
Uncertain use (availability) of non-fertilizer N

12. Temporal variability
Relationship of potential yield and use of non-fertilizer N

13. Temporal variability
Estimated fertilizer N (70% eff.) to maximize wheat yield

14. Temporal variability (corn)
Irrigated corn yields (Mead, NE, 15-yr)
Check plot yields
Mean = 84 bu/acre
CV = 36
Fertilized max yields
Mean = 135 bu/acre
CV = 16
Fertilized vs. Check
R2 = 0.36

15. Temporal variability (N Response; RI)
Winter wheat RI
Range = 1.0 to 4.1
Mean = 1.9
CV = 38
Irrigate corn RI
Range = 1.1 to 3.5
Mean = 1.8
CV = 34

16. Spatial variability

17. Problems with conventional N management
Assumes temporal variability is negligible.
Yield potential is the same each year.
Supply of non-fertilizer N to crop is constant and negligible.
N application rate for field is the same each year.
Assumes preplant fertilizer-N will be efficiently used.
Assumes field(s) will be uniform.
Constant N rate for entire field(s).

18. Solutions Estimate N response in-season. N-Rich Strip
90 N Preplant
N-Rich Strip
March 20
Limited preplant N
45 N Preplant

19. Solutions Estimate N response in-season. 90 N Preplant RINDVI = 1.46

20. Solutions
Estimate N response in-season.

21. Solutions
Provide in-season estimate of yield (INSEY)
YP0
YPN
YPMAX

22. Solutions
Measure and treat spatial variability

23. Solutions
Measure and treat spatial variability, in-season

24. Solutions
Measure and treat spatial variability, in-season

25. Solutions Measure and treat spatial variability, in-season Apply most
N as a
top
dress

26. Economic estimates
Average Gain = $10.73/acre/yr

27. Economic estimates
Average Gain = $17.13/acre/yr

28. 2002 Field trials 10 trials using 60-ft boom sensor-applicator.82
34.6 92 20 21 52
Farmer Check 17
100
39.8 79 23 15 41
VRT 81
Yld (bu/a)
Total N
Late
Early
Preplant N
Treatment
Obs.
Return ($/Ac)
Topdress N
Web site.

29. Conclusions Temporal variability can be managed.
Create N-Rich Strip in each field.
Evaluate yield potential and N responsiveness in-season using sensor.
Spatial variability can be managed on a fine resolution (<m2)
New management strategy improves profitability for farmers.
New management strategy reduces field loss of fertilizer.