Not every plant we cultivate for food grows from seed in soil. Some don't grow from seed, either naturally or by our choice, because we want to perpetuate the characteristics of a particularly useful genome.
- Vegetative Reproduction
- Any plant reproduction that doesn't involve the reshuffling of chromosomes which results from sexual reproduction. Wikipedia has an excellent article on this topic.
- Plant Propagation
- This is a more general term that includes both reproduction from seed and vegetative reproduction. Again, Wikipedia has this covered.
There are also some plants that naturally don't grow in soil, but here we're mostly interested in cultivation methods not involving soil, except perhaps as an inert granular medium used only for mechanical support.
- Generally thought of as a way of producing fish, crustaceans (shrimp, lobsters, crayfish) or gastropods (snails, clams), aquaculture can also be a way of producing food those animals eat, or plant matter for other uses. Everything from suspended phytoplankton to vascular plants anchored on the bottom or floating on the surface can contribute to the biomass available to/from the system. Besides being productive in itself, aquaculture combines well with other practices, because, whether due to the presence of microorganisms or the waste products of animals, the water makes good fertilizer.
- Hydroponics & Aeroponics
- These are two variations on the theme of growing plants in a nutrient solution without soil, although, in the case of hydroponics, an inert granular medium may be used for mechanical support. Aeroponics is distinguished by the use of mist to keep the roots moist, rather than fluid water, obviating the need for supporting structures sufficiently strong to hold up the mass involved in using large amounts of water, and also avoiding the possibility of anaerobic conditions developing.
- Aquaponics is the combination of aquaculture and either hydroponics or aeroponics, where water from aquaculture is used as a fertilizer, and perhaps also plants produced using that water are fed to animals in the aquaculture environment. This cycling of nutrients can result in a highly productive systems which make good use of both space and available light energy.
Either way, whether using soil or not, aquaculture can be an integral part of the system.
Also either way, whether using soil or not, whether outdoors, or in polytunnels or permanent greenhouses, or in racks under light from LEDs, or even growing mushrooms in the dark, there's a place for robots, lots of robots, maybe even billions of robots.