July-August - 12

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provides a more integrated picture of prior N nutrition
up to the point of sampling. In both cases, values are
compared to published thresholds by crop stage to
determine if additional N is needed.
Sensitivity is a key strength. By analyzing N
compounds within the plant, emerging deficiencies may
be detected early. In addition, where multiple elements
are analyzed, it can be valuable for troubleshooting.
Interpretation is often complicated by high variability
and confounding factors. Variety, plant stress,
environmental conditions and other factors unrelated
to N can influence concentrations, particularly for sap
nitrate-N.
Tissue testing also suffers from similar variability
limitations as soil testing, and while it can indicate if
more N is needed, it is a poor predictor of how long N
may be sufficient going forward. As a result, continuous
plant sampling is needed to confidently delay or
eliminate additional N applications.
Canopy remote sensing
Canopy remote sensing (RS) involves analyzing
pictures - though the wavelengths of light used can
This image of a squash field was taken by a drone
for the nitrogen management experiment at MSU.
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12 | JULY/AUGUST 2023
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Equipment that makes dollars & 'sense'
vary widely. Sensors ( " cameras " ) can be handheld,
tractor- or pivot- mounted, or flown on drones
or satellites. A wide diversity of metrics are then
derived as indicators of current plant N status, with
values compared to " thresholds " (often based on
high N reference areas in the field used to reduce
confounding factors) to decide if an N application
is needed, very similar to tissue testing. However,
both plant growth and spectral characteristics -
greenness - can be measured.
The key strength of RS is making the necessary
sequential monitoring more feasible by lowering time,
expense and labor. Benefits include greater accuracy,
spatial completeness and growth context. However,
accessibility to growers remains low in many areas,
and the cost and complexity of analysis further limits
adoption. An important question is also whether RS
methods can detect emerging deficiencies soon enough
to intervene, which likely depends on crop, growth stage
and the capabilities of evolving sensing technologies.
Michigan State University research
Our lab has been studying the use of drone-based
remote sensing for N management relative to traditional
tools in field vegetables. Drones give us a way to test
high spatial and temporal resolutions now that may one
day be available from satellites, with less hassle. We've
found that drone-based metrics can predict yield better
than leaf N or petiole nitrate-N in carrots, squash,
tomato, celery and other vegetables, and have a similar
capacity to distinguish differences in plant N status over
time. However, more research is needed to understand
performance in guiding N applications and how best to
implement RS for N management within commercial
vegetable cropping systems.
http://www.philbrownwelding.com
July-August

Table of Contents for the Digital Edition of July-August
