Sustainable underground agriculture (fantasy)

[OremLK]

Looking to brainstorm a little on this one. What I want to do is have a virtually self-contained underground society in a fantasy world with medieval technology, plus magic.

Assume that, by means of magic, large caverns are illuminated with sufficient light for plant growth. Assume also that these caverns have been illuminated like this for thousands of years.

Underground rivers and lakes would also be accessible.

Taking these suppositions as a given, could large-scale hydroponic agriculture be accomplished underground, with medieval technology? How might this be done, if so? What kinds of plant and animal life would be likely to have taken hold in the long period that energy (effectively sunlight) was available within the caverns?

Thanks for your help.

[veinglory]

Well assuming your magic light is sun light (which seems a bit 'tidy') you could grow anything. But I would expect some changes in crops that never get rain--losing any water trapping adaptations. I would suggest perhaps going more for low and no light staples, like fungi that could grow like above ground or below ground (more like potatoes)--to make the whole culture seem more subterranean.

[Sarpedon]

Of course it could. the question would be, why hydroponic? if there's light and plant growth for thousands of years, there'd be soil.

as far as what plants, you should think of what kind of plants would get their seeds down there. Mosses and ferns emit lightweight spores, that could conceivabley blow or drift down there, or be carried by animals stuck to their fur. Fruit-eating bats would be an ideal vector for plants. Also mice and other subterraneon mammals might bring down the seeds of grains and grasses. Pine trees? Probably not. Avocados? Cocoanuts? No way.

[stephenf]

You Don't need hydroponics to grow food.But without rain you would need some kind of irrigation ,by means of channels etc.You could grow rice in paddy fields.There are air plants, that don't grow in the ground .As far as I know they are not edible ,but you could Lie about that bit.

[dempsey]

I think this'd get more love in the general SFF forums than in "Science Fact."

[OremLK]

The problem I see with soil is that there's not much weathering underground--well, not the kind that produces soil, anyway. There could be organic detritus from moss and such, and to a lesser extent from animals, but is that actually enough to grow crops? And wouldn't the soil be depleted from nutrients much more easily, thus damaging the sustainability of the whole thing?

[Pthom]

I think this'd get more love in the general SFF forums than in "Science Fact."
Yup. Moved. :)

[stephenf]

A lot of rich soil is created by flooding ,the receding water leave a nutrient rich sediment .I think a underground delta region may work

[Mr. Chuckletrousers]

You can manufacture soil with sufficient manure and broken/powdered rock. If this underground society has been mining or hollowing out caves then presumably it has access to plentiful broken/powdered rock. Also, since it is a society then it will have access to manure (i.e. from the citizens). If there are bat colonies in nearby caves then you could also use their guano. Just mix that shit up, make sure it is plenty aerated and watered, and you have the perfect growing medium for plants of all kinds.

Here's what you would need to successfully grow plants underground (you can decide whether a medieval-like society can do this):

the magical light
access to broken rock or the ability to make broken rock
lots of manure / guano
the ability to mix manure and rock together
the ability to bring water to the 'fields' (e.g. by aqueducts and tunnels and ditches)
air, including carbon dioxide
plant seeds
plows and plow animals (maybe, not all plants need this)
an understanding of what you need (see list)

[OremLK]

You can manufacture soil with sufficient manure and broken/powdered rock. If this underground society has been mining or hollowing out caves then presumably it has access to plentiful broken/powdered rock. Also, since it is a society then it will have access to manure (i.e. from the citizens). If there are bat colonies in nearby caves then you could also use their guano. Just mix that shit up, make sure it is plenty aerated and watered, and you have the perfect growing medium for plants of all kinds.

Here's what you would need to successfully grow plants underground (you can decide whether a medieval-like society can do this):
the magical light
access to broken rock or the ability to make broken rock
lots of manure / guano
the ability to mix manure and rock together
the ability to bring water to the 'fields' (e.g. by aqueducts and tunnels and ditches)
air, including carbon dioxide
plant seeds
plows and plow animals (maybe, not all plants need this)
an understanding of what you need (see list)

Thanks, this is very useful and just the sort of information I was looking for! I appreciate the help.

[Nivarion]

a thought i have on this is, that an underground cavern would be the same temperature all the time. with a fixed light source, that i assume would be the same intensity all day and night, you would be able to grow huge plants, year round.

therefore, you would have a lot of crowding in these caves since the people would have more food.

[OremLK]

That's somewhat true, but there can be limiting factors as well. For instance, you can say that these people don't actually control the artificial light, they just have it in certain areas due to magical artifacts. If you could only grow food in those areas, your food production would obviously be limited by that.

[Izunya]

Let's see. No rain, so the people would irrigate their fields by flooding them, which makes rice an obvious staple. Probably the growing season would have less to do with temperature—caves are pretty stable temperature-wise—and more to do with how much water the underground rivers carry, which might vary based on surface rainfall. And since caves are uniformly cool (I'm assuming the magic lights don't give off enough heat to signify) you'd want to look at temperate crops only. No pineapples or bananas.

Also, you might want to spend some time thinking about whether the magic light is exactly like sunlight or not. It could conceivably be weaker and still sustain plants. So maybe Undersider vegetables (or whatever this place is called) have broader, darker leaves than their surface counterparts. Maybe trees are unknown, which would lead to bushes and domestic vines as the main fruit-bearers (or at least berry-bearers).

I'd also have your underground dwellers supplement their diet with mushrooms. I mean, as crops go, mushrooms are easy. They like it cool and dark and they grow on stuff you were going to throw out anyway. And there are more edible varieties than most people think.

Izunya

[Smiling Ted]

Let's see. No rain, so the people would irrigate their fields by flooding them, which makes rice an obvious staple. Probably the growing season would have less to do with temperature—caves are pretty stable temperature-wise—and more to do with how much water the underground rivers carry, which might vary based on surface rainfall. And since caves are uniformly cool (I'm assuming the magic lights don't give off enough heat to signify) you'd want to look at temperate crops only. No pineapples or bananas.


There are warm - even hot - caves. They're near thermal vents, magma chutes, that kind of thing. And some caves are basically poisonous...they have mineral deposits that will kill unadapted creatures. That could be useful for story purposes. Cave systems have often been used for mushroom farms in Belgium, France and the United States.

[Nivarion]

it wouldn't be required to flood the fields, if they had say aquaducts. they would be able to control the water, despite changes in the underground rivers using reservoirs.

with consistent light in any spot, and human ingenuity the society would be very sustainable.

hmm just a though, Does the light move? if it did that would make a million complications.