Using aerial photography & fertigation to fine-tune N management Peter Scharf MU Agronomy Extension.
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Transcript of Using aerial photography & fertigation to fine-tune N management Peter Scharf MU Agronomy Extension.
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
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 uptakeReduced time = reduced risk of N loss
N uptake timing: good match with fertigation
% o
f up
take
Growth stage
Corn N uptake
100
0V6 V12 VT milk
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
Losing N & yield (sandy soil)
150 lb N timing Yield (3-year ave.) Preplant 147 2/3 PP, 1/3 12-leaf 159 1/3 PP, 2/3 12-leaf 167 8-leaf 179 12-leaf 185 4-way split 184
Source: University of Minnesota 2 of 3 years had heavy June rains
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?
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 high3% yield loss if first N applied from chest
high to 8 feet tall15% yield loss if first N applied at silking
Timing of fertigation when main N application was missed
-20
0
20
40
60
80
100
120
0 5 10 15 20
time of 200 lb N application
yie
ld r
es
po
ns
e t
o N
(b
u/a
c)
plant 18” 36” 80”
Eight production corn fields, 1997
Situation #2: Unable to apply N at normal time
Soil is wetYou may be tempted to rush irrigation in order to get N to the cropThis may not be necessary
Injection system needs enough capacity to apply most of crop N need through the pivot
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
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
Diagnosing N loss
This is the hard partDeciding if additional N is neededPrioritizing fieldsDeciding how much N to apply
Aerial view is bestCover more ground faster than other ways
of doing diagnosisBetter overall assessment
Diagnosing N loss from an airplane
Photographs are better than memoryThere are some pilots around who will do this for a reasonable priceThere are companies considering developing an aerial photo/recommendation map serviceThis is not commercially available at presentA seat-of-the-pants interpretation of where to put more N and where to put less will probably be fairly accurate
Situation #4: Fine-tuning N management
Expect a yield response only when corn has visible N stressGene Stevens: fertigation experiment on Watkins farmN stress measured with chlorophyll meterHigh N stress: 35 bu/acre responseLow N stress: 10 bu/acre responseNo N stress: no response
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 NAmount of N needed
Applying these relationships to photos of pivot fields can guide fertigation decisions
An example from project Team Up!
darkest,okay
lighter,needs N
Photo July 3, 2003Atchison County
15% lighter
25%lighter
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
An example from project Team Up!
darkest,okay
lighter,needs N
Photo July 3, 2003Atchison County
Zero N
50 N 100 N
An example from project Team Up!
darkest,okay
lighter,needs N
Joe Henggeler calculates variable fertigation $2000 better than uniform
No response
10 to 30 bu
30 to60 bu
Image analysis predicts: