1. Using aerial photography & fertigation to fine-tune N management
Peter Scharf
MU Agronomy Extension

2. Why fertigate? Avoid N loss from leaching
Unable to apply at normal time due to weather
Respond to N loss or deficiency
Fine-tune N management
Gives a yield boost that earlier applications can’t achieve

3. Reason #1: Avoid N loss from leaching
N uptake mostly from knee-high to early grain fill
Later application reduces the window of time between N application and uptake
Reduced time = reduced risk of N loss

4. N uptake timing: good match with fertigation
Corn N uptake
100
% of uptake V6
V12 VT
milk
Growth stage

5. Reason #1: Avoid N loss from leaching
Especially on sandy soils
N loss can cause yield loss
Same N rate but applied later through pivot = lower risk
This is the same concept as sidedress N being lower risk than preplant

6. Losing N & yield (sandy soil)

7. Situation #2: Unable to apply N at normal time
2003 rainfall, April 1 - June 15

8. Situation #2: Unable to apply N at normal time
This is not an uncommon situation in Missouri
When it happens, what are the considerations for amount and time of fertigation?

9. Timing of fertigation when main N application was missed
Corn is less sensitive to N timing than you might think
28 experiments, mostly on-farm:
No yield loss if first N applied by chest high
3% yield loss if first N applied from chest high to 8 feet tall
15% yield loss if first N applied at silking

10. Timing of fertigation when main N application was missed
Eight production corn fields, 1997
plant
18”
36”
80”

11. Situation #2: Unable to apply N at normal time
Soil is wet
You may be tempted to rush irrigation in order to get N to the crop
This may not be necessary
Injection system needs enough capacity to apply most of crop N need through the pivot

12. Timing of fertigation when main N application was missed
As soon as possible, but don’t rush to irrigate on wet ground
Even if delayed until silking, fertigating will be highly profitable if the main N application was missed due to weather
No later than two weeks after tasseling

13. Situation #3: N was applied, but it was lost
Northeast Missouri, wet May and June weather

14. Situation #3: N was applied, but it was lost
2002—two experiments where applied N was lost
Both near Brunswick/Miami
Soil N good on May 22 (but 9 inches of rain since April 26)
9 more inches of rain, May 22 to June 15
40 and 60 bu/acre responses to added N

15. Diagnosing N loss This is the hard part Aerial view is best
Deciding if additional N is needed
Prioritizing fields
Deciding how much N to apply
Aerial view is best
Cover more ground faster than other ways of doing diagnosis
Better overall assessment

16. Diagnosing N loss from an airplane
Photographs are better than memory
There are some pilots around who will do this for a reasonable price
There are companies considering developing an aerial photo/recommendation map service
This is not commercially available at present
A seat-of-the-pants interpretation of where to put more N and where to put less will probably be fairly accurate

17. Situation #4: Fine-tuning N management
Expect a yield response only when corn has visible N stress
Gene Stevens: fertigation experiment on Watkins farm
N stress measured with chlorophyll meter
High N stress: 35 bu/acre response
Low N stress: 10 bu/acre response
No N stress: no response

18. Tools for fine-tuning N management
Aerial photographs
Applicator-mounted spectral radiometer

19. Aerial photos to fine-tune N management
Research at the University of Missouri has related corn color from aerial photos to:
Corn yield response to N
Amount of N needed
Applying these relationships to photos of pivot fields can guide fertigation decisions

20. An example from project Team Up!
Photo July 3, 2003
Atchison County
15%
lighter
25%
lighter

21. Interpreting lighter areas—watch out for:
Tassels
Tasseled corn appears lighter than corn that has not yet tasseled
If only part of the field has tasseled, it will appear lighter than the rest of the field
Rather than being the N-deficient areas, these areas are farther along and may have the BEST nitrogen supply of anywhere in the field
The influence of soil color (if the corn has not reached full canopy)
The influence of corn size on how much soil you see

22. An example from project Team Up!
Photo July 3, 2003
Atchison County
50 N
100 N
Zero N

23. An example from project Team Up!
Joe Henggeler calculates variable fertigation $2000 better than uniform
Image analysis predicts:
10 to
30 bu
30 to
60 bu
No response

24. Fertigating corn: summary
Reliable way to supply N
reduces risk of N (& yield) loss on sandy soils
Good tool for managing unexpected N loss
Potential for supplying needed N very accurately with no overapplication