There are things I look forward to seeing every season.
In spring, I watch for “mighty plants” that emerge from the ground with enough force to heave the soil above ground. These botanical weightlifters—the bulbs, grasses, and other emergent plants—pushing up soil that was compressed by a blanket of snow never fail to impress me. I am in awe of the strength of plants.
Seeing bulbs coming up all around me inspires lots of questions. I want to understand how this is possible and I want to test their strength. So I spent a few weeks playing around with this phenomenon in the Learning Center’s Boeing Nature Laboratory.
To begin, I wanted to demonstrate that seeds will lift soil in a pot. I soaked bunch of wheat seeds overnight and planted them in a pot. I covered them with a generous amount of potting soil (about a 1/2-inch layer) and I tamped the soil down gently so that it would be compressed—like the topsoil might be after a winter of snow cover. Three days later, I had results! I sprayed the soil disk to give it a little adhesion, so I could see how long it would hold together as the grass lifted it up.
That was so much fun, I tried the same thing with a bunch of bean seeds.
This demonstration was pretty easy and impressive. It is a simple activity to illustrate how plants and other living things change their environment to suit their needs (which is a disciplinary core idea in Next Generation Science Standards for kindergarten). I recommend doing it in the classroom or at home, just for fun.
This is just the beginning. I will be sharing the results in a future blog post. But before I do, I would like to make a few points about the nature of science and how scientists work.
Science is a collection of established facts and ideas about the world, gathered over hundreds of years. It is also the process by which these facts are learned. Science is both “knowing” and “doing.”
Discoveries start when you watch nature and ask questions, as I did in watching spring bulbs come up. Before beginning an experiment, scientists play. They mess around with materials and concoct crazy ideas. They are constantly asking, “I wonder what will happen if I do ___ ?” That is when discoveries actually happen.
Scientists do formal experiments with purpose, hypothesis, procedures, results, and conclusions after they think they have made a discovery. They use the experiment to test their discovery and provide convincing evidence to support it. In some cases, the experiment disproves a fact or idea, which is a different kind of new understanding about the world.
I have to agree with Boyce Tankersley, the Garden’s director of Living Plant Documentation, who recently wrote “The SciFi Rant.” Those of us who lean toward botany instead of horticulture are more interested in growing plants to yield ideas rather than meals. In my continuing investigation, I have two goals, and neither is to produce anything to eat.
First, I want to determine the strength of sprouting seeds and see how far I can push them. For example, how many bean sprouts will it take to lift a coconut? I want to find a standard way to measure seed strength.
Second, I want to establish a reliable method for experimenting with seed strength so teachers and students can replicate the procedure, modify it as needed, and use it for their own investigations without going through the awkward phase of figuring out the best way to do this.
The Martian: Many of us watched and loved the movie. Some of us read the book. A few of us got inspired to use the story to teach plant science to students.
The Martian by Andy Weir tells the fictional story of NASA astronaut and botanist Mark Watney, who becomes stranded alone on Mars and has to figure out how stay alive until the next NASA mission returns to rescue him. He plants six potatoes and successfully propagates a crop of potatoes in Martian dirt fertilized with human poop.
The story got me wondering if we could replicate Martian soil with local ingredients and use it for plant experiments. So I contacted the Garden’s soil scientist, Louise Egerton-Warburton, and asked her if this was possible. She responded with a recipe:
Mix two parts crushed volcano rock, two parts basalt dust, one part sand, plus 0.2 parts feldspar
Autoclave (heat to very high temperature) three times to kill microbes
You know you work in a great place when you can ask a colleague for directions for making Martian soil and you get an immediate, enthusiastic response with suggestions for how to use it. I acquired the materials and cooked up a batch.
One important thing I must mention: technically speaking, this mixture is not truly “soil.” Soil is the upper layer of material on the Earth that serves as an ideal medium for growing plants. It contains inorganic minerals from weathered and broken rocks combined with organic material from the decomposed remains of dead plants and animals. Real soil hosts microscopic bacteria and fungus that facilitate a cycling of nutrients through the ecosystem and convert minerals to a form plants can absorb and use. Soil also supports many little macroscopic critters, like worms and mites, that increase the porosity and affect other properties of the mixture.
The substance we would find on the surface of Mars is called regolith, which is mineral particles that result from weathering of rocks. Since my mixture is an approximation of what might be found on Mars, but made from Earth-sourced ingredients, it should actually be called simulated Martian regolith. But that’s a mouthful, so from here on I’m going to call it Martian soil and ask you, dear readers, to accept the inaccuracy for the sake of simplicity. OK?
I took my Martian soil and set out to answer my first question: what happens if we try to plant seeds in this stuff? Put another way, is it possible to grow plants in Martian soil without adding anything? To answer this question, I took a polystyrene egg carton and planted marjoram seeds (because I had some laying around) in my Martian soil and in some Earth potting soil for comparison.
The Martian soil is completely different from the potting soil in appearance and texture, and it responds differently when watered. Shortly after the seeds germinated in all of the cells, the Mars side went south. It didn’t hold water very well; it dried out and became hard, almost like concrete. It was no surprise that all of the seedlings on the Mars side died soon after germination. Plants on the Earth side continued to grow and thrive.
In the book, Watney used a bucket of Earth soil and human waste to amend the Martian soil for his potato crop. The book and the movie differ on this part—likely because the process required to make Martian soil suitable for growing potatoes was long and tedious. It wouldn’t make for riveting cinema. Instead of cultivating the soil over time, movie-Watney planted a spoonful of rehydrated human poop next to each piece of potato.
While movie-Watney’s actions remind us of stories about the Pilgrims teaching the indigenous people to place a piece of fish next to each kernel of corn to improve the crop yield, there are some problems with applying this method to our Martian soil. The Martian soil would still lack sufficient organic materials and therefore not be able to hold water (as I demonstrated with my marjoram seed experiment). There would be an insufficient population of microbes to break down the human waste. Furthermore, the fecal matter might be so concentrated in nutrients that it could actually be toxic to the potato plants. I don’t believe it would actually work.
This compelled me to do some myth busting for my next experiment: since “humanure” would be unsafe—and gross!—I used worm poop, or vemicompost, which I have in plentiful supply from worm bins in our Learning Center nature laboratory. Also, I discovered that you can order “Martian Regolith Simulant” from a company online (who knew?). Although it’s expensive, it saved me the effort of crushing rocks, so I’m using it from now on.
This time I planted russet potato pieces and some sweet potatoes that had sprouted in my pantry at home (oops!) in azalea pots. I set up three conditions: Martian soil, Martian soil plus vermicompost, and Earth potting soil for comparison.
Underlying these experiments (and few other I have tried) is a basic investigation of what plants need to survive. By testing to find the right combination of Martian soil and amendments, and limiting solutions to those that could be transported by a spaceship to another planet, we are using engineering practices because we are trying to solve a problem. This is real-world science and engineering that students could do in the classroom.
Besides satisfying my personal curiosity, these experiments are paving the way for some science lessons we are writing for teachers and students.
If you are a teacher interested in learning more about how to teach NGSS-aligned life science lessons using Martian soil, sign up for our workshop, STEM: Growing Plants in Martian Soil on Saturday, December 2, 2017. And watch for other Martian soil training opportunities in the future.
We may never need to grow crops in Martian soil. But as we investigate the challenges of colonizing another planet, we can learn more about what plants need to thrive and also develop a genuine appreciation for how amazing our Earth soil is.