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 “Using this technology, we can possibly see the nitrogen stress
early on, before tasseling. That means farmers won’t need to
wait until the end of the season to see the impact of their
nitrogen application decisions,” says Kaiyu Guan, assistant
professor in the Department of Natural Resources and
Environmental Sciences at the University of Illinois, and Blue
Waters professor at the National Center for Supercomputing
Applications. He is also principal investigator on a new study
published in IEEE Journal of Selected Topics in Applied Earth
Observations and Remote Sensing.
Being able to detect and address changes in crop nutrient status
in real time is vitally important to avoid damage at critical
periods and optimize yield. In general, existing satellite
technology cannot achieve both high spatial resolution and high
revisiting frequency (how often a given satellite comes back to
the same spot above the Earth). Alternatively, drones can detect
nutrient status in real time, but they usually can only cover
local areas; thus, their utility is limited in scale.
CubeSats bridge the gap between existing satellite technology
and drones. With more than 100 of the relatively tiny satellites
currently in orbit, Guan says, “CubeSats from Planet get down to
a 3-meter resolution and revisit the same location every few
days. So, right now we can monitor crop nitrogen status in real
time for a much broader area than drones.”
Guan and his collaborators tested the capabilities of both
drones and CubeSats to detect changes in corn chlorophyll
content, a proxy for the plant’s nitrogen status. The
researchers focused on an experimental field in Central Illinois
during the 2017 field season. Corn in the field was
nitrogen-stressed to varying degrees due to multiple nitrogen
application rates and timings, including all nitrogen applied at
planting, and split applications at several developmental
stages.
The analyzed field was one of several in a larger study looking
at nitrogen rates and timing, set up by Emerson Nafziger,
professor emeritus in the Department of Crop Sciences at
Illinois and co-author on the study.
“The idea was to see how much effect timing and form of nitrogen
fertilizer would have on yield. This study allows an evaluation
of how well the imaging could capture yield responses to
nitrogen applied at different rates and times,” Nafziger says.
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The scientists compared images from drones and
CubeSats, and their signals matched well with tissue nitrogen
measurements taken from leaves in the field on a weekly basis. Both
technologies were able to detect changes in chlorophyll contents
with a similar degree of accuracy and at the same point in the
season.
“This information generates timely and actionable insights related
to nitrogen stress, and so could provide guidance for additional
nitrogen application where it’s needed,” Guan says.
The implications go beyond optimizing yield.
“The low cost of nitrogen fertilizer and high corn yield potential
motivates farmers to apply extra nitrogen as ‘insurance’ against
nitrogen deficiency that lowers yield. But applying more nitrogen
than the crop requires is both a financial and environmental risk,”
says Yaping Cai, graduate student in Guan’s research group and lead
student author on the paper.
Guan adds, “A better tool for fertilizer use, enabled through new
satellite technology and ecosystem modeling, could ultimately help
farmers to reduce cost, increase yield, and meanwhile reduce
environmental footprint for a sustainable agricultural landscape.”
The article, “Detecting in-season crop nitrogen stress of corn for
field trials using UAV- and CubeSat-based multispectral sensing,” is
published in IEEE Journal of Selected Topics in Applied Earth
Observations and Remote Sensing [DOI: 10.1109/JSTARS.2019.2953489].
This research was supported by NASA and the Illinois Nutrient
Research and Education Council.
Co-authors include Yaping Cai, Kaiyu Guan, Emerson Nafziger, Girish
Chowdhary, Bin Peng, Zhenong Jin, Shaowen Wang, and Sibo Wang. Guan,
Nafziger, Chowdhary, and Peng are affiliated with the College of
Agricultural, Consumer and Environmental Sciences at the University
of Illinois.
[Sources: Kaiyu Guan, Emerson
Nafziger
News writer: Lauren Quinn] |
