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Detection of early season corn nitrogen stress improved with nanosatellites

Trying to determine when and how much nitrogen should be applied to corn continues to be a challenge for growers. Research at the University of Illinois has shown that nanosatellites could provide an answer.

“Using CubeSats 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 the principal investigator on a new study published inIEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing.

In order to avoid damage at critical periods and optimize yield, having the ability to detect and address changes in crop nutrient status in real time is critically important. Today's satellite technology generally cannot achieve both high spatial resolution and high revisiting frequency (how often a satellite comes back to the same spot above the Earth). While drones may be able to detect nutrient status in real time, they typically only cover local areas, which means their usefulness is limited.

With more than 100 of the miniature satellites currently in orbit, CubeSats bridge the gap between today's satellite imagery and drones. 

“CubeSats from Planet get down to a 3-meter resolution and revisit the same location every few days," Guan says. "So, right now we can monitor crop nitrogen status in real time for a much broader area than drones.”

Comparing Capabilities of Drones and CubeSats

To detect changes in corn chlorophyll content, which is a proxy for the plant's nitrogen status, Guan and his team of collaborators tested the capabilities of both drones and CubeSats in a field in central Illinois during the 2017 growing season. Corn 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 Illinois field was one of several in a larger study looking at nitrogen rates and timing. It was 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.

Comparing images from drones and CubeSats, the scientists learned that their signals matched well with tissue nitrogen measurements taken from leaves in the field weekly. 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.

Yet, the scientists believe 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.

“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 their environmental footprint for a sustainable agricultural landscape," Guan concludes. 

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