If humans are ever going to colonize Mars – which we will, if NASA and Elon Musk have their way – then we need to make sure we can grow food locally. Now a team from Wageningen University & Research has found that earthworms might soon need a name change: the creatures, a crucial part of making soil fertile, can thrive and reproduce in simulated Martian soil.

The red dust that covers the surface of Mars is so barren and dry that scientists are hesitant to call it "soil" at all: the word implies the presence of organic matter from plants and animals. Without that, the Martian regolith is mostly dust and rock that won't be much use to future farmers without some prior treatment.

After the Curiosity rover sent back its analysis of the Mars "soil", NASA found the closest match here on Earth to be volcanic soils from Hawaii. Previous studies using that simulant have had mixed success in growing crops, with the best results sprouting from tests that used fertilizers like freshly-cut grass. Potatoes, it turns out, could be grown in Red Planet greenhouses, but they need some help.

Manure is still one of the best fertilizers, and while farmers on the Red Planet will probably have to use their own like in the movie The Martian, the Wageningen researchers used pig slurry in their tests. They added the manure to samples of the Mars simulant and samples of "silver sand" growing rocket salad, then compared the two.

"The positive effect of adding manure was not unexpected, but we were surprised that it makes Mars soil simulant outperform Earth silver sand," says Wieger Wamelink, lead researcher on the project.

After the rocket had germinated, the team then added to some of the pots another crucial element that had been missing until now: worms. These slimy invertebrates play a key role in making Earth soil healthy by digesting dead organic matter and excreting a potent fertilizer that helps release nutrients like nitrogen and phosphorus. Their constant burrowing also helps lighten up the soil, allowing air and water to seep through better.

That's an important improvement for the simulated Mars soil, which water struggled to soak through in previous tests. Altogether, the tests showed that the combination of worms and pig slurry helped the plants grow in Martin soil, and the worms not only thrived but reproduced.

"Clearly the manure stimulated growth, especially in the Mars soil simulant, and we saw that the worms were active," says Wamelink. "However, the best surprise came at the end of the experiment when we found two young worms in the Mars soil simulant."

That raises hopes for our ability to grow greens on the Red Planet some day. And rocket won't be the only thing on the menu: the researchers say they've also had some success with green beans, peas, radishes, tomatoes, potatoes, carrots and garden cress. After testing for heavy metals and alkaloids, the veggies were all deemed safe for human consumption.

Source: Wageningen University & Research

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