Some scientists are questioning whether soil is necessary for space agriculture
Aeroponics, as one soilless cultivation process is called, grows plants in an air or mist environment with no soil and very little water.
In 1997, NASA teamed up with AgriHouse and BioServe Space Technologies to design an experiment to test a soilless plant-growth system on board the Mir Space Station. NASA was particularly interested in this technology because of its low water requirement
See Anuradha K. Herath's article for details.