With aspirations of establishing human outposts on Mars, NASA is collaborating with astrobiologists to identify optimal crops for this extraterrestrial agriculture. To maximize yields in these unique conditions, researchers are exploring innovative planting techniques. A recent study published in PLOS One delves into the potential of intercropping, an age-old practice of growing multiple crops in close proximity, to boost harvests on the Red Planet.
Simulating the Martian Landscape
For long-term human habitation on Mars, a steady supply of nutritious food is paramount. While the resourceful methods employed by fictional astronaut Mark Watney in “The Martian” are intriguing, real-life Martian colonists will require more practical solutions. Scientists are replicating the Martian environment on Earth to develop these solutions. Mars boasts an atmosphere 100 times thinner than Earth’s, primarily composed of carbon dioxide, nitrogen, and argon. Future Martian colonies will likely reside in pressurized greenhouses mimicking Earth’s atmosphere, with the right mix of oxygen, nitrogen, and carbon dioxide.
“The best ‘Martian environment’ is actually simply a greenhouse with controlled conditions including temperature, humidity, and gasses,” explains Rebeca Gonçalves, an astrobiologist at Wageningen University & Research in the Netherlands and co-author of the study.
For this experiment, Gonçalves and her team constructed greenhouses at the university to simulate a Martian growth environment. They evaluated crop performance in a replica of Martian regolith, the loose, rocky Martian surface material. Standard potting soil and sand served as control groups. Additionally, organic Earth soil and nutrients were incorporated into the sand and Martian regolith samples to enhance water retention and root development.
Selecting Suitable Species
Peas, carrots, and tomatoes were chosen for this simulated Martian farm. A previous study (2014) demonstrated their ability to thrive in Martian regolith. Gonçalves highlights that while their growth potential was established, their focus was on a different question: how companion planting and intercropping could enhance crop yields. These three choices also boast significant nutritional value for future colonists.
“We selected them for their rich antioxidant, vitamin C, and beta-carotene content,” says Gonçalves. “This is crucial because these nutrients are lost entirely during food dehydration, the primary method for supplying food on space missions. Therefore, cultivating fresh produce rich in these nutrients is essential for a Martian colony.”
Interestingly, these crops also exhibit complementary characteristics, making them ideal companion plants. Peas, being legumes, play a key role in the intercropping system by “fixing” nitrogen. Nitrogen fixation is the process by which certain plants and bacteria convert atmospheric nitrogen into a usable form (ammonia) for plant nutrition. This, in turn, benefits neighboring plants and reduces the need for additional fertilizers. According to Gonçalves, this optimizes resource utilization for plant growth on Mars.
“Carrots were chosen to improve soil aeration, thereby enhancing water and nutrient uptake by companion plants,” Gonçalves explains. “Tomatoes were included to provide shade for the temperature-sensitive carrots and offer climbing support for the peas.”
Yielding Results on the Red Planet
All three species displayed decent growth in the Martian regolith, producing over half a pound of produce with minimal added nutrients. Notably, tomatoes grown alongside peas and carrots in the intercropping setup outperformed control tomatoes grown in isolation. The intercropped tomatoes exhibited higher biomass and potassium content.
However, intercropping in this simulated Martian regolith appeared to have a negative impact on carrot and pea yields. These plants thrived better when grown alone. In future experiments, the team aims to refine the treatment of the simulated Martian regolith to potentially increase yields with intercropping, allowing carrots and peas to benefit similarly.
“The success observed for one of the species is a significant finding that paves the way for further research,” remarks Gonçalves.
The team was also surprised by the positive effect of intercropping in the sandy soil control group. This technique benefited two out of the three plant species, suggesting potential applications for Earth’s agricultural systems. Climate change is causing an increase in sandy soils, and this study contributes to ongoing efforts exploring how intercropping can mitigate this issue.
The team’s future research endeavors aim to achieve “a completely self-sustaining system utilizing 100% of local Martian resources.” This would significantly enhance the financial viability of future Martian colonies, reducing their dependence on resupply missions.
“If we can unlock the secret to regenerating poor soils while developing a high-yielding, self-sustainable food production system—exactly the goal of Martian agriculture research—we will have found a solution for a lot of the issues we are having here on Earth as well,” concludes Rebeca Gonçalves.
