Mars explorers could use complicated mechanical systems to produce oxygen and filter waste, and eat food carried from Earth. Or they could just save a lot of hassle and plant crops.

A model of Martian gravity's effects on water flow, nutrient dynamics and root-feeding microbes suggests it's possible to farm in the Red Planet's soil.

"In terms of biogeochemistry and in interms of hydraulics, I'm pretty confident it could work," said Federico Maggi, a University of Sydney biogeochemist who conducted the simulation.

Growing plants in soil on Mars might seem old-fashioned for those raised on the futuristic prospect of hydroponic or aeroponic agriculture, in which crops sprout soil-free nutrient broths or mists.

But in recent years, starry-eyed biologists have come to appreciate the importance of soil-dwelling microbes to plant roots and soil processes. Moreover, soil-based agriculture is backed by thousands of years of human-based research and development, and millions of years of natural evolution.

"Mechanical systems are very reliable over short-term expeditions," said Maggi. "But soil can control itself. In terms of operation error, it's more reliable. Plants provide more benefits in terms of energy and health. And real soil performs operations that other systems cannot."

However, there are many unknowns about extraterrestrial agricultural biology. Among the most important is how low gravity will affect the flow of water and nutrients, and in turn microbes. Once water and nutrients get into the plants, capillary action will take care of the rest. But getting them there is the key.

"If there's low gravity, water will not flow down so quick. The transport of nutrients would also be slower. If transport of nutrients towards root microorganisms is not fast enough, it will suffocate them," said Maggi.

In a July Advances in Space Research study, Maggi and University of California, Berkeley biogeophysicist Céline Pallud simulated both Mars- and Earth-gravity root processes using BIOTOUGHREACT, a well-regarded model of soil nutrient transport and microbe dynamics developed at the Lawrence Berkeley National Laboratory.

The simulation suggests that slower water transport is actually a good thing, preventing water from falling through the soil and being lost, along with the nitrogen it absorbs on the way.

At Mars gravity – about one-third of Earth's – up to 90 percent less water would be needed than in a terrestrial greenhouse, said the researchers. Much less nitrogen would also be needed.

"You don't have a leaching of nutrients. The nutrients you put into the soil, remain in the soil. You don't lose them," said Maggi. The simulated bacteria thrived on all this extra food, reaching densities between five and 10 times the usual.

According to University of Florida agricultural engineer Ray Bucklin, an advisor to the Mars Foundation and author of several NASA reports on Mars greenhouse design, the nitrogen savings could be especially important.

"Mars is nitrogen-depleted," and any fertilizer would need to come from Earth, he said. "And in terms of the soil microbes, they would be in a pretty beneficial situation."

Bucklin warned that the real-world water savings would likely be much less than 90 percent. "Water movement through a plant has several other things that influence it besides what happens in the soil," he said. At low gravity and low atmospheric pressure, "water movement through the plant would be accelerated."

But Bucklin still said the study "is interesting and needed to be done."

According to NASA plant physiologist Raymond Wheeler, most extraterrestrial crop researchers have used hydroponics or artificial soil, "which simplify their testing and allow easy recycling of water and nutrients." But real soils "might have certain advantages," including better waste degradation and a built-in buffer against water shortages or equipment malfunction.

Maggi plans to perform more simulations on how other important plant nutrients, such as potassium and iron, will behave.

Of course, the ultimate tests will come on Mars itself, and NASA's budget problems have put a damper on such dreams. But even if NASA has problems, other programs – especially the European Space Agency – intend to have people on Mars by mid-century. Private enterprise could also sponsor the voyage.

"We already have the engineering to put a base on Mars," said Bucklin. "If Bill Gates wanted to blow his whole fortune, he could do it right now."

Image: NASA.

See Also:

Citation: "Martian base agriculture: The effect of low gravity on water flow, nutrient cycles, and microbial biomass dynamics." By Federico Maggi and Céline Pallud. Advances in Space Research, online publication, July 16, 2010.

Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.