The average yield for corn in the US for 2021 was 176.5 bu/ac. This is around 11,9 ton/ha. For 10 ha, a total of 119 ton.[1][2]
How many people this would feed is hard to tell, because it depends on the kind of corn. Some corn is meant for human consumption, some other for livestock feed (which in turn is meant for human consumption. But as a rough estimate one can add these two to find an order of magnitude.
In 2008, the USDA broke down the usage for maize, with 133,4 Mton (5250 Mbs) for livestock and 8,3 Mton (327 Mbs) for human consumption. That year, the US population was around 303.5 million people, so that gives an average of 467 kg (1030 lb) a person each year.[3][4]
So those 10 ha would produce enough corn for 240 people for a whole year.[5]
This comment might come a little bit too late, but I wouldn't want to give the impression that these numbers suggest using urine as fertilizer is self-sustainable. It is not self-sustainable, and it might not be sustainable in the long term. For many reasons:
- First of all, urea as a fertilizer is not completely effective, because some of it will be drained. Urea can be treated for slow release, but this requires processing. And even in this case, some of it will just be degraded by bacteria (some bacteria will turn it into compounds that plants can use, but generally urea content will fall with time).
- I used total nitrogen from urea, but in reality a part of that nitrogen does not come as urea.
- I also used average yields, which depend on the usage of more powerful fertilizers. Fertilizing with urea alone will lead to smaller yields.
Let's say that average yield woud drop to 50% and that I would need not 53 bu 80 people's yearly urine. That would mean I would only provide enough corn for 120 people each year, for a input of 80, which gives a ratio of 3:2. Seems good enough. Unfortunately this is not the case.
Human urea is the result of human diet and metabolism, which gets nitrogen from many different protein sources. Self-sustainability means that those 120 people would have to eat only corn and meat from corn-fed livestock, or trade this for other protein sources (which would only externalize this unsustainability: some other people's diet would have to change). Even if it were possible to keep up with the same urea output without severe weight loss, this would not be enough:
- First of all, plants use nutrients to grow many inedible parts, and that is an important drain of nitrogen. This also means all plants, not just the ones we eat.
- Livestock would still need food sources other than corn. The above assumptions assume well-fed cattle.
Finally, as someone already noted in another comment, human urine contains a significant amount of salt, and without its removal this could lead to excess salinization that would render the soil infertile in the long term. And the higher concentrations of urea needed could also worsen the already present problem of eutrophication.
But using urine might still be a great help with local, temporary unavailability of better fertilizers.
