Using aerial photography & fertigation to fine-tune N management

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 uptake • Reduced time = reduced risk of N loss

N uptake timing: good match with fertigation Corn N uptake 100 % of uptake 0 V6 V12 VT milk Growth stage

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)

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

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 high • 3% yield loss if first N applied from chest high to 8 feet tall • 15% yield loss if first N applied at silking

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

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

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 Northeast Missouri, 1998--wet May and June weather

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 part • 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

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

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

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

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

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

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

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

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

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

Using aerial photography & fertigation to fine-tune N management