An Experiment by the 5th-graders at Leonardtown Elementary School in St. Mary’s County, Maryland

What is the Best Medium in which to Grow Carrots on Mars: A Growth Experiment on Soil, Compost, Hydroponics, and ‘Martian Rock’ as Substrates for Carrot Growth

The Fifth Grade Class at Leonardtown Elementary School in St. Mary’s County Maryland
Teachers: Jody Fagnano, Cheryl Wight, Christine Guy, Stephanie Thomson, Daniel Grünberg
Principal: Contina Quick-McQueen

Abstract

An important aspect to living on and colonizing Mars is the ability for humans to grow their own food. A question exists as to whether plants can be grown on Mars and if so, what kind of substrate can be used for their growth. This experiment compared growing 4 media for growing carrots: soil as a control, compost, hydroponic substrate, and ‘Martian Rock’. The carrots grew best on compost and second best on soil. Based on our results, we believe that carrots can be grown on Mars assuming that they get the proper sunlight, atmosphere, water, temperature, and space. Extrapolating from our data, we suggest using pulverized Martian rock mixed with available composted biological waste and seeded with healthy Earth soil to terraform Martian rock into Martian soil.

Introduction
If humans are to colonize Mars, food production will be required to sustain the colonists. Although for shorter trips food can be brought along, it takes up valuable space and is expensive to transport. Growing crops on Mars may be important not only to sustain people, but the psychological benefits of gardening can be of benefit as well.

There are several potential problems to growing plants on Mars. Plants need water. Luckily, water has been found to exist on Mars and can potentially be harvested and used for this purpose (Patel, 2016). Plants also need carbon dioxide (CO2) for photosynthesis. Carbon dioxide is abundant on Mars and makes up over 95% of the gasses in the Martian Atmosphere (Sharp, 2012). Although the Martian atmosphere is only 1% as dense as that of Earth (Sharp, 2012), the amount of CO2 needed to grow plants may be able to be pumped from the atmosphere into a greenhouse that will protect the plants from the effects of the extreme cold and that will maintain a proper atmospheric pressure. LED lights may be used to provide supplemental lighting for the growing plants (Herridge, 2016). Mars rocks have all the nutrients that plants need, but they may not be in the proper proportions or may not be easily available to the plants (Jordan, 2015). The question we decided to investigate was whether carrots would grow better in Terran soil, compost, ‘Martian rock’, or in a hydroponic system. Terran soil served as the control, but it is heavy and would be prohibitively expensive to transport from Earth to Mars. Compost is available from bio-waste generated by the colonists and could be “seeded” with beneficial organisms commonly found in soil. Martian rock is lacking these beneficial organisms, but is readily available on Mars and would conceivably be the least expensive option. Hydroponics uses a medium such as vermiculite that is lighter to transport than Terran soil, but requires macro and micro nutrients to be separately added to the system, which adds to transport costs and requires continuous inputs that may not be readily available on Mars.

Materials and Methods
Holes measuring ¼” in diameter, spaced about 3” apart, were drilled about 3” above the bottom of four plastic bins measuring 20” x 12”. These holes provided drainage while still allowing for a liquid reservoir to accumulate in the bottom of the bin. One bin was filled with topsoil. Another bin was filled with compost. A third bin was filled with vermiculite and the fourth bin was filled with red lava rock to simulate Martian rock. All materials were bought from a local hardware store.

Carrot seeds were planted in each of the bins and lightly covered with the medium in the bin, except for the red lava rock where the seeds were allowed to remain uncovered. The three bins containing topsoil, compost, and lava rock were moistened with tap water. The bin with vermiculite was watered with Miracle Grow ™ fertilizer at the recommended dosage. The four bins were placed in a south facing window.

After three weeks, the carrots were thinned and measurements of the thinned plants were taken for comparison purposes. Observations were made at three weeks, two and a half months, and four months when the plants were harvested.

Results
At three weeks after planting, the following observations were made:
Measurements were made of the entire plant, including roots, stems, and leaves, and were recorded from leaf top to root tip.
Carrot length in the Soil bin – 73.12 mm average. The plants had a long, white, and thin root.

Carrot length in the Compost bin – 67.98 mm average. There were fungi present. The plants were leaning towards the light. The texture of the soil was fine. There were one hundred and 2 carrots, quite a bit more than any other bin. The plants had seed caps. Some of the plants were flat on the ground.

Carrot length in the Martian Rock bin – 74.1 mm average. There were 22 plants. Some of the plants were dead. Some plants were stuck underneath the rocks.

Carrot length in the Hydroponics bin- The group of children working on this bin did not find an average, but wrote down the longest and the shortest carrots. The shortest was 50 mm and longest was 80 mm. The carrots were wilting. They were pale green. The plants had fewer leaves.

At two and a half months after planting, the following observations were made:
No measurements of the carrots were made at this time due to the carrots not showing a lot of growth.
Soil bin: Some of the plants were dead. The soil was dry. The plants looked thin. It looked like the plants did not get enough sunlight because they were scraggly, long, and thin.

Compost bin: It looked like the plants were growing well. The compost was wet. Half of the bin had taller carrots while the other side had shorter carrots. This appeared to be due to unequal sun coverage. White fungal spots were on the compost.
Hydroponics bin: The plants looked pale green but healthy. More plants were growing compared to the previous observation. Stems were thicker at this time.

Martian Rock bin: Almost all of the plants have died. There were only 6 stems and they were long and thin. The location of the bin could have affected the carrots due to little sun. Seeds had fallen deeply in between the rocks and as a result covered the carrots.

At four months after planting, the following observations were made:
Soil: The plants were fairly numerous. Some of the stems were red. Some of the leaves were yellow. Because no further nutrients were added to the soil we surmised that this could be from little nutrients or not enough sunlight. Some of the roots looked like they were developing out of the ground. Only two plants had recognizable carrot-type tap roots. The roots that were not developing were white. Measurements: tallest root was 76 mm, smallest root was 25 mm. The biggest leaf was 50 mm and the smallest leaf was 15 mm. The sum of five carrots weighed 0.1 g.

Compost: The plants were tall and densely packed. Their color was bright green. The plants were falling over. Six plants produced small carrot-type tap roots. Fungus was prevalent throughout the compost. The compost was wet. Measurements: tallest root was 88.9 mm, smallest root was 38.1 mm. The biggest leaf was 406.4 mm and the smallest leaf was 203.2 mm. Six carrot plants weighed 5.5 g.

Hydroponics: The plants were sparse and were wilting. Some were prostrate. The carrot stems and leaves were pale. The plants were evenly spaced in the bin. Measurements: biggest root was 65 mm and the smallest root was 50 mm. The biggest leaves were 125 mm and the smallest leaf was 75mm.

Martian rock: There were only 3 carrots growing on the edge of the bin and everything else was dead. The plants were greener than the previous observation. The roots were light green and thin. Measurements: biggest root was 63.5 mm and the smallest root was 38.1 mm. The largest leaf was 50.8 mm and the smallest leaf was 38.1 mm.

Discussion
The compost bin produced the best results in our experiment, followed by the soil control and hydroponic bin respectively. The “Martian” rocks produced the poorest results. None of the carrots grew to eating size in the four months that we conducted this experiment.

There were several factors that may have impacted our study. The plants were planted in the winter which is not the best time to grow carrots. The plants were all placed in front of one large south facing window, but not all bins, and not all plants received an equal amount of light. Plants not receiving as much light may have resulted in stems that were longer and scraggly, had yellowing leaves, and that ultimately may have died.

The compost bin likely had the most amount of nitrogen available to the plants. Nitrogen is needed for growth and that is likely why the carrots in this bin were the healthiest and greenest of our plants. However, we were concerned about the large presence of fungus in the compost that may eventually have outcompeted the carrots or even preyed upon the carrots. The fungus may have grown so well not only because of the nitrogen, but because the compost was so wet.

The bins did not receive the same amount of water, partially due to helpful people who watered the plants without our knowledge. Although we tried to control for this by placing drainage holes on the side of the bin that would allow for a reservoir of water but enable excess water to drain, it had the effect of diluting the amount of nutrients that were received by the hydroponics bin.

In addition, to sunlight and water, we did not control for temperature. Carrots growing closer to the window may have been colder than carrots growing in the same bin further away. This may have impacted their growth, however it should have impacted each bin in the same manner.

We believe that the “Martian” rock would have produced better results if we had a way to crush the rock into smaller particles. The rocks were fist-sized and easily crushed the carrot plants, was hard to work with, and didn’t cover the plant roots well to keep them from drying out.

We were surprised by these results, because in the beginning of the experiment, most of us thought that the hydroponics bin would produce the best results. However, hydroponics are very dependent upon the nutrients added to the system and we do not believe that our hydroponic plants received enough nutrients due to the overwatering with tap water.

If we were to conduct this experiment once again, we would have planted the carrots more sparsely so that we would not have to have weeded as much. Alternatively, we should have more aggressively weeded the carrots in the compost bin. This bin had so many carrot plants that even after weeding, the plants were still very dense. This overcrowding may have reduced carrot yield and stunted individual growth.

Another factor that should be considered with regard to growing carrots on Mars is the high amount of perchlorates in the Martian soil. These would need to be removed or experiments would need to be done to determine how well different types of plants grow in perchlorates and whether they are taken up by plants where they could be toxic to those who eat them.
We also learned that just because the leaves grow well, it doesn’t mean the carrots roots grew well. Since we eat the roots and not the leaves, this is an important point. Carrots also take a long time to grow.

Based on our experimental observations and conjecture, we believe that the best way to grow vegetables and crops on Mars would be in a greenhouse that uses supplemental LED lights so the plants get enough sunlight. We also think that compost from biowaste, seeded with beneficial organisms, would provide the nitrogen that is lacking on Mars. However, since there is not much nitrogen on Mars, it may still be necessary to provide more nitrogen that is shipped from Earth. The goal would be to make a healthy Martian soil by adding compost to ground-up Martian rock.

Conclusions
Our experiment showed that compost was the best type of medium to grow carrots. However, due to the lack of controls, we have low confidence in our results. We invite other elementary schools to duplicate our experiment and improve upon it. We hope that together we can help NASA determine how we can best feed astronauts and even colonists that travel and live on Mars.

Citations:
Herridge, L. (2016). NASA Plant Researchers Explore Question of Deep-Space Food Crops. Retrieved from https://www.nasa.gov/feature/nasa-plant-researchers-explore-question-of-deep-space-food-crops

Jordan, G. (2015). Can Plants Grow with Mars Soil? Retrieved from
https://www.nasa.gov/feature/can-plants-grow-with-mars-soil

Patel, N. (2016). A Year After Discovering Water on Mars, Humanity Finds a Second Home. Retrieved from https://www.inverse.com/article/21601-liquid-water-mars-one-year-anniversary-colonization-nasa

Sharp, T. (2012). Mars’ Atmosphere: Composition, Climate & Weather. Retrieved from
http://www.space.com/16903-mars-atmosphere-climate-weather.html

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