1. REVIEW

3. N Rich Strip
Farmer Practice

4. Response Index variable from year to year in the same field
2004
1995
Long term N-P-K Experiment #222 ( )
Dr. Billy Tucker

5. y ±1δ = 68% of values (2/3 of the population) y ±2δ = 95% of values y ±3δ = 99.7% of values_
= 68% of values
-1δ
+1δ
-2δ
+2δ _ y
Assume: differences are due to X

6. Assume: differences are due to X

7. Gyles Randall, 2006 Problems - sidedress N
1. We have limited equipment for the later SD applications.
2. We see more and more 20 and 15” rows, which poses a huge problem.
3. Quick N uptake is problematic, depending on rainfall.
4. Will yield-drag occur if some “hidden” N deficiency occurs around the VT and R1 stages.
Farmers see these challenges as one big RISK, and risk in today’s environment plays a large role in farmer’s decision making.

9. Average, 8 Farmer Sites, 04-05 N Rate Yield GP NUE kg/ha kg/ha $/ha %
Check
SBNRC
RCS
Farmer Practice
SED 379
$0.59 kg N $0.12 kg grain ($0.27/lb N, $3.40/bu) SBNRC (Sensor Based Nitrogen Rate Calculator)

10. Issues
Corn Weakness - you don't know whether or not this rate will "run out" later in the season. 
Long-term experiments have shown that there are years where the check plot (No N Fertilizer ever applied) produced near maximum yields. 
Have years where the demand for fertilizer N is less (and highly dependent on the environment), and other years where it is cool and dry and the demand for fertilizer N is greater. 
RCS approach can help to determine how much the environment delivers and that is variable year to year  

11. HISTORY of METHODS for Determining Fertilizer N Rates

12. N Rate (kg N/ha) N Uptake (kg N/ha) NDVI50 10 20 40 30 30
N Rate (kg N/ha) 40
N Uptake (kg N/ha) 50 20 60 70 10 80
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NDVI
Linear NDVI - N rate scale previously used
to determine variable N rates based on NDVI.
New approach for determining N rate which
needs to be further researched.

13. Increased soil background Increased red reflectance
NDVI = NIR - Red
NIR + Red
Red nm
NIR 750-1x106 nm
Increased soil background
Increased red reflectance
Decreased NDVI
In this region, NDVI is
influenced by
(a) color. 50 10 20 40
In this region, NDVI is
influenced by
(a) soil
(b) % coverage
(c) color 30
N Rate (kg N/ha) 40 30
When NDVI is low, we need a method of determining whether the value is a function of poor coverage or of other factors, such as low N uptake. Cause-effect relationships at both ends of the scale have not been well established; applying N were it may not be needed or applying no N where some is needed. We do not have a clear picture of where NDVI and N uptake are linear.
N Uptake (kg N/ha) 50 20 60 70 10 80
0.2
0.3
0.4
0.5
0.6
0.7
0.8
NDVI

14. Tipton, January 15, 1998, Feekes 5
Fertilizer N Rate
Percent Coverage
NDVI

15. N Fertilization Strategy Based on Potential Yield (YP0) and Forage N Uptake
What about YPN and RI?
Fertilizer N Rate ? ?
kg/ha kg/ha kg/ha
Potential Yield (YP0) Grain N uptake Forage N uptake Difference Topdress N Rate

16. RI= high RI= medium RI= low N Rate, kg/ha 0 1 2 3 4
Nitrogen Rate Based on RI and Potential Yield
RI= high
100 80 60 40 20
RI= medium
N Rate, kg/ha
RI= low
Potential yield, Mg/ha (INSEY)

17. YPN < YPMAX 2001 1 Predict RI Predict YP0 Predict YPN based on RI3
2001
YPN < YPMAX 1
Predict RI
Predict YP0
Predict YPN based on RI
Fertilizer N = GNUP-FNUP/0.7 2 2 3 4 1 4