Nanosatellites improve detection of early-season corn nitrogen stress
Dove satellite, a CubeSat model from Planet Labs Inc. (Photo by Planet Labs Inc.)

For corn growers, the decision of when and how much nitrogen fertilizer to apply is a perennial challenge. Scientists at the University of Illinois have shown that nanosatellites, known as CubeSats, can detect nitrogen stress early in the season, potentially giving farmers a chance to plan in-season nitrogen fertilizer applications and alleviate nutrient stress for crops.

“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,” said Kaiyu Guan, assistant professor in the U of I Department of Natural Resources and Environmental Sciences and Blue Waters professor at the National Center for Supercomputing Applications.

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 said, “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 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 2017. 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 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.

“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,” said Yaping Cai, graduate student in Guan’s research group and lead student author on the paper.

Guan added, “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.”