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 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 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

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

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

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

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

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

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