What would be the ideal conditions for a farm-world?

Question

As title says, but for added context, here goes: The setting is a rather intricate take on hard-magic meets science-fiction, and takes place in a highly advanced milky way populated mostly by humans and other vaguely-humanlike aliens that share most, if not all the same physiological nutritional needs – That being, Carbohydrates, Fats, Proteins, Vitamins, Minerals and Water. Due to the exponential growth of population accelerated by relatively cheap hyperspace travel, discovery of several habitable exoplanets, and ease of construction of massive space structures that can support over a billion inhabitants with ease, I find that food production might be a bottleneck, and something hard to explain in this setting, as the overall population will cross the dozens of trillions – Though, water and minerals would not be concerns, as offworld mining operations would generate more than enough leftover for any purposes, and, with enough technology, all water is indefinitely reusable.

That being said, I want to know if a highly technologically advanced earth be would capable of providing sufficient nutrition for all those trillions of inhabitants, and through which means would that be possible – And, if it is not possible, which I highly suspect it’s not, what would be the ideal conditions, climate, atmosphere, substrate composition, and crop choice on an exoplanet or exomoon dedicated exclusively to farming: a Farm-world? Would a single planet suffice, or would multiple smaller planets be necessary and/or more efficient for that purpose? What advantages an exomoon has over an exoplanet, if any?

After some study, I found that planets with very dense, carbon-dioxide rich atmospheres, that are also closer to their star would benefit greatly due to boosted photosynthesis and metabolism – However, a planet with those traits would also be victim to a runaway greenhouse effect, killing everything on it.

Workers are NOT to be considered – any and all workforce needed can be easily provided by machines, humans need not apply. Likewise, power and electrical needs are not issues, as solar and fusion technology is in surplus, and energy can be beamed from orbit if necessary. Interplanetary and Interstellar logistics are also facilitated by Alcubierre and Hyperspace drives, but getting to and from orbit might remain difficult – With that in mind, we can focus only on the matter at hands, which is what would be the ideal conditions for accelerated crop growth on a farm-world.

Answer 1

Think No Planet, Aeroponic, GM farms

For plant farms, there are a myriad of different requirements to control very accurately to optimise yield:

• Light (not just quantity of light, but what frequencies of light)
• Water
• Humidity (this is actually very important and must be set just right)
• Fertiliser/Nutrients (contrary to popular belief, you can only farm the same plot of land a certain amount of times before the soil is drained of Nitrates, and require replenishing)

In this respect - our current open field farms on Earth can only be optimised so far, as these above requirements are limited. There is only so much useful light that falls on a given square metre of Earth, for only part of the day. There is only so much water that can be placed, and fertiliser inefficiently delivered via spray or pellets over fields.

At my work, we design aeroponic and hydroponic farms. Unlike natural open-field farms, these do not have the hindrance of the above, and you can illuminate plants 100% of every day, with finely tuned humidity, water and nutrient levels. You can stack each plant tray on top of each other too, to optimise space.

In fact, I think in your scenario, to feed trillions upon trillions of people I would do the following:

• Not be on a planet. Gravity is not necessary for plants to grow. In fact, having your food production within a major gravity well is a major hindrance in getting nutrients in and plants out. Have large floating structures in space (like big bubbles). If you must have planets, make them dozens and dozens of small moons.
• Not use sunlight. Yes that's right, sunlight is actually not the best light for optimal growing of plants. Artificial, constant, red-frequency light is the best and therefore you need to imagine your plants would be internal, not exposed externally to the sun. Use solar power to supply energy to your optimised internal lighting system. If it must be a planet, having a binary red-light star system with constant red light would be best.
• Use Aeroponics. Instead of Hydroponics, Aeroponics places the nutrient (including Nitrate) mix with water into the atmosphere to be absorbed by each plant, each plant being suspended in air. This would make it toxic for humans to enter, but the growth speed of plants would be highly accelerated without requiring soil, or water medium for nutrient supply. If you wanted a natural planet to do this, you need a high Nitrate atmosphere (note: NOT nitrogen gas as in our atmosphere which is too hard for plants to utilise, but ammonium nitrate or nitrogen dioxide) and this will get used up eventually, so you need to replenish it over time. On Earth, lightning is one of the main mechanisms to convert Nitrogen N2 gas to Nitrogen Dioxide to then be slowly absorbed into the soil, as the Nitrogen bond is so strong it needs a lot of energy to break. If it must be a planet or moon, with a nitrogen atmosphere, there must be a lot of lightning on it to break it down to be useful for plants.
• Use GM. Yes, it is a controversial topic, however genetically modifying the plants to optimise growth rate and nutrient outcomes is actually the best way forward if lives are at stake. By doing this you are not limited to the current crop of wheat, rice, vegetables and lettuce, but instead expand to plants that can be designed to deliver optimal nutrition and taste. Research is currently underway to create plants that can freeze for transport without loss of cellular lining (causing them to taste bad upon defrosting) - this would be needed if your farms are far away (as in light years) from your consumers.

So in summary, a space station with internal aeroponic, artificially lit, robot farms farming GM crops is the best. You can make it as big as you want to feed trillions, but keep in mind you don't need much volume to feed trillions if all the above are optimised.