Seeds burrowing into ground

Mimicking seed burrowing could lead to applications in robotics

Image credit: Jung et al

South Korean researchers have created mathematical models to describe how seeds burrow into soil in response to humidity. Their findings could help find more efficient methods to penetrate the soil, with applications in agricultural robotics.

The inspiration for the project came to Professor Ho-Young Kim of Seoul National University, after watching a plant documentary. He saw that some plants have seeds which “drill” into the soil using a coiled appendage – known as an awn – which responds to changes in humidity.

Professor Kim brought together colleagues to investigate these “ingenious mobility strategies” of plants. Using geranium seeds in their study, they observed how these awns bury themselves rotationally into the ground. These awns are coiled like helices, which expand when they absorb moisture. In humid environments, therefore, the awn is forced to straighten out.

If a seed is anchored, this deformation creates a force against the soil. This force helps to bury the seed towards a better, deeper germination environment. This particular motion minimises the drag force of the soil against the seed.

“It was a surprise to us that the plant can produce effective motions without muscles. We immediately investigated plant species with self-burrowing seeds and identified plant species using similar digging strategies,” said Wonjong Jung, a senior researcher at Samsung Advanced Institute of Technology.

“Although the seeds of some plants such as wild wheat have simple curved awns that exhibit only bending motions, the seeds of other plants with helical awns can generate rotary motions for digging. We thought that it was highly probable that the seeds spin themselves to facilitate digging.”

These seeds are an example of biological geometry; in this case being used to provide plants with almost muscle-like capabilities.

“Our work illuminates the surprising functionality and beauty of natural design,” said Professor Wonjung Kim, of Sogang University. Beyond this understanding, the mathematical models resulting from the work have direct applications to agricultural robotics; particularly into soil-digging machine design.

"To obtain environmental information such as soil pollution in inaccessible areas such as space planets, battlefields, or disaster areas, small robots are needed," Professor Kim said.

"Our research has demonstrated a reduction in particle drag by rotation, which informs an efficient intruder design method for digging robots. Furthermore, self-burrowing awns provide inspiration for designing non-motorized robots that respond to various stimuli such as heat, light, and humidity."

Many traditional agricultural responsibilities are beginning to be taken over by automated machines, such as with harvesting fruit, shearing sheep, milking cows, and weeding. Driverless tractors are commercially available, and drones are being increasingly used to monitor farming conditions and spray pesticides.

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