Solar energy has a maximum output of 1120 W/m2 at the surface of the earth. So theoretically, a square meter could support 10 people. But there are one or two efficiency losing steps that throw this all off.
There's only light for half the day. Plants only are about 3-6% efficient at absorbing solar energy. The plants also are only taking up a fraction of the ground they're using, let's be liberal and say half. Then there's the whole 'how much of the energy the plant used was actually converted to edible calories' question, which is beyond my ability.
Multiplying that together, the best I can imagine is around 12 m^2 per human.
I'd love someone to show me a mistake in that logic, because I am super excited about things like this. I know I'm going to own one of these someday in the future.
This would mean one acre of land would sustain about 40 people (or 100 per hectare).
Taking wikipedia's number of 13,958,000 km^2 of arable land in the world, this would mean a maximum world population of 137,963,876,580, which is about 20x the current world population.
Of course, this assumes equal quality of land to the land in your rough calculations, and I am guessing your number is assuming far more intensive cultivation than is typical (typical numbers I've seen are 1-2 acres / person).
Having said that, I'll now go on to say: with one inhabited planet there are limits to resources, but the limits to human resourcefulness are undefined.
Edit: the not eating animals is not in a vegatarian way. I love meat. But if you want to fully sustain yourself on the smallest area possible, animals do not aid your cause.
On an all-potato diet, assuming intensive cultivation (40,000 lbs/acre yield) you could feed about 20 people on one acre. That's 200m^2 per person. For a varied diet that might contain chicken and eggs, 1000m^2 (a quarter acre) is more reasonable.
Also, it's not a practical minimum but a theoretical one, like supposing we had so many plants absorbing light that it's dark underneath them, etc.
In reality, potatoes can do about 17m cals per acre per year, and a human needs nearly 1m per year. In short, Matt Damon definitely wasn't growing enough potatoes (in the film version at least).
Anyway, in Japan the amount of rice that one person historically has eaten for one year is 1 koku (which is about 150 kg). The yield for rice is about 0.41 kg per square meter. So you need well over 300 square meters to grow enough rice for one person for one year. That doesn't include other vegetables or fish (or whatever).
In Walden, Thoreau describes self sustenance and living off the land. I believe he talked about farming a quarter of an acre, which is about 1000 square meters. Many people doubt he was able to rely completely on that quarter acre.
You can get some extra efficiency if you build vertical grow systems, but even your 12 m^2 is a pipe dream. Their 3.5 m^2 system will provide snacks at best. So I think you are right to be skeptical.
As for this technology being used on a larger scale, I'd be really interested to see the cost for a similar setup over a few thousand hectares, and what sort of efficiencies might be gained compared to our current system. However I'm not convinced it'll replace our machinery any time soon.
The other interesting use for this would be, if it gained a large enough user base, the sharing of different planting setups and rotations for nutrient replacement. i.e planting crop x and y in rotation, or interrow with crops a and b.
I think this will be the real win of this technology eventually. Most if not all first world farmers understand that over the lifetime of their farm doing proper crop rotation increases yields but there is still a very reasonable instinctual reluctance to give up the short term profit of a high yield crop in order to plant a rotation crop of less profitable plants to keep the soil up correctly. Evening out that profit per field would probably be a great boon to operations that are too small to rotate entire fields.
It would also probably be an excellent way to get non farmers involved in the food production chain, especially in semi-rural areas. I grew up just in front of a community pasture which served as a grazing ground for three or four different farmer's herds and a couple of people who kept a couple of milk cows for local cheese making and stuff like that. Extending that concept to plants would be great, a giant community garden where people could plant crops that they are interested in and receive the yields at the end of the growing period. Larger farming outfits could plant around the regular people and ultimately keep costs down because of subsidy. Round out five or six gardens with some cash crops like wheat, soy or corn while locals use some of the field to grow their own grocery vegetables.
> Round out five or six gardens with some cash crops like wheat, soy or corn while locals use some of the field to grow their own grocery vegetables.
Like allotments? https://en.wikipedia.org/wiki/Allotment_(gardening)
But for the average consumer, this doesn't seem particularly economical. Automation of this kind of thing only makes sense when you have a significantly larger field. I still think this is a great idea, but I think its reach is a bit overstated.
Take soybeans. Typically you want to plant around 130,000 seeds per acre. I estimate by the video that it takes about three seconds to plant a single seed. That's four days just to plant a single acre of land. The John Deere DB120 planter claims to be able to plant 75 acres per hour.
Naturally, you can add more of these machines, but with that goes up the cost and complexity. I'm not so certain the economics would favour such a device.
The nerd in me has my credit card out and is ready to overnight one of these things to my backyard.
The suburban dad in me scoffs because one of the best parts of having a garden is planting stuff with my kids and helping them water and care for the garden.
Robots vs kids....
Hmmm. That gives me another idea...
..and the construction set: http://opensourceecology.org/gvcs/
That's a bit snarky. I was pretty pumped with the project at first, but it really seemed poorly run, and also seemed to ignore a lot of prior art when designing hardware. Their compressed block machine does seem fully thought out and functional at least, but their first tractor snapped in half on its maiden voyage, and the replacement looks like a post-apocalyptic bobcat. There's a reason most farmers aren't using bobcats in the field.
Anyways, neat idea, and I hope it inspired others to focus on open source hardware for agriculture and small-scale civilization.
When I looked at the progress of the machines I had a sneaky feeling it might have slowed down - I was interested in the "aluminum extractor from clay" a few years back :)
For a more novel approach to farming, see the combination of fish tanks and planting, called "Hydroponics":
Autonomous weeding robots which roam big fields and take out weeds one by one are being demoed by several manufacturers. Here's the most practical-looking one, out in a huge field of beets, quietly killing weeds one at a time.
As well as sensors that will pickup weeds from dirt.
This would be in the middle of those two problems. There isn't a dense crop to pick the weeds out of, but it's probably slightly too dense to just pick them up from the dirt.
With this farmbot I can imagine it would be doable.