Self-planting, drill shaped seeds

Seed carriers that can drill themselves into the ground to boost the success of sowing rates have been engineered by researchers in America. They've taken their inspiration from a grass species called erodium, which has a corkscrew-shaped seed with a sideways-pointing anchor tail at one end. When this lands on the ground, penetrating moisture swells the tissue, triggering the spiral to unfurl against the anchor, driving the seed into the soil. By working out how nature does this, Carnegie Mellon scientist Lining Yao has developed a way to copy and improve on the process using small pieces of wood that can be loaded with a seed cargo and then deployed as aerial seeding devices, for instance for regenerating tracts of woodland or conservation areas on a massive scale. Seeds that plant themselves in this way are much less likely to become mouse and bird food, or dried out by the sun...

Chris - And that's what you were seeking to make a replica or an equivalent of. Did you do it the same way?

Lining - On the material side, you need a stiff material. You need it to be biodegradable because we don't want to retrieve the seed carriers. We started to think about wood because it's a very abandoned, accessible biomaterial that are cellulose rich and also are known to have this moisture responsive behaviour. But we had to compare different kinds of wood. Eventually we chose white oak. We also have to think about the geometry. So one thing we did a little bit smarter than in nature is that we are introducing two extra tails. So basically the natural erodium only has a single tail. So when you drop it on the floor, it tends to land flat. But in order for it to drill, it has to lift its own body up by leveraging some crevices on the ground that limit the type of soil erodium can function in. So in our case, we introduced two extra tails. So when you drop our seed, they tend to land on the floor with a specific angle. And that angle helped improve the drilling efficiency.

Chris - How did you make these things. When one pictures this, the erodium seed, it looks almost like a little mini windmill with the seed at the bottom of a stalk. How did you make that, because you've effectively copied that with the three arms coming off of yours. How do you make it?

Lining - Basically it has two major steps. First, we need to process wood into veneers and then cook them in a chemical solution to make the wood more compliant. And the second step is we molded on top of a 3D printed mould that we tailored beforehand. Basically we have to wind it into the coil manually.

Chris - Got it. So you 3D printed the geometry you wanted, that you knew ought to work the right way, and then you mould the wood onto that. It's almost like forming it onto a mould to make it adopt that shape. And then you've got your seed carrier, but made of white oak.

Lining - Exactly.

Chris - How big is each one?

Lining - We make a range. So the smallest could be maybe one centimetre in height and you can make all the way about 10 to 15 centimetre in height. And again, this highly depends on what seeds or other things you want to carry with the carrier. Small vegetable seeds only need a very small carrier, but pine seeds, for example, are much larger. You need a larger body to carry them.

Chris - How did you test it to find out if it would really do what you were hoping it would?

Lining - We have done both in lab controlled tests and eventually we also brought it outdoor. So we've conducted five rounds of tests with hundreds of seeds in two geographic locations. We watched the weather broadcast right before heavy rain came. We threw them on the floor and then we monitored how effectively we can drill.

Chris - And what was the germination rate when you did this compared to if you just threw the seeds on the floor?

Lining - Across the five batches, we got about a 66% anchoring rate. And among the ones that anchored about a 60% germination rate.

Chris - And what about if you just threw seeds on the floor, the same sorts of seeds, how many of those would successfully germinate?

Lining - I really wanted to conduct this test, but we haven't got a chance to do this exact comparison. But we do know if you try to germinate pine seeds with broad casting from the aeroplane, the germination rate is 2 to 10%.