Aeroponics

Aeroponics is the growing of plants with the roots exposed to the air. Water and nutrients are misted or sprayed on the roots.

Advantages

This method provides several advantages to a colony on Mars:

• Water Conservation
• Disease Control
• Increased Crop Yield
• Very simple 'ecology' (i.e. you don't have to worry about the health of the soil.)
• No substrate, as compared to hydroponics that usually require a substrate, that needs to be produced and adds complexity.

Disadvantages

• Aeroponics plants do not have a buffer of soil to temper changes or any type of technical problem. So they need constant monitoring and are somewhat less stable than soil grown cultures.
• Monocultures are susceptible to disease. (Though nothing says your Aeroponics garden needs to be a monoculture.)
• Salt buildup, and basically any contaminant buildup in the water, needs to be controlled.
• Biological contamination may be possible through the water spray.

The long term need for aeroponics in a martian settlement is debatable. Plants will produce excess biomass, and all living beings will produce waste, that can be incorporated into soil. So the amount of soil available to a settlement naturally grows with time. As the biomass of the settlement grows, the entire habitat ecosystem becomes more stable. An ecosystem based on aeroponics might be susceptible to catastrophe because it has very little buffer.