How much land does a person need?
November 27, 2007 10:42 PM   Subscribe

What is (or how can I find) the maximum/average food value of x acres of farmland?

I can find things about the increased land-per-person needed for meat-eaters and industrialized society, but no basic estimates of how much land is needed to feed a person, or how many people x amount of land can feed. I realize this would vary according to crop, climate zone, etc. I must be framing my searches incorrectly because Wikipedia, Google, and the UN Food and Agriculture Org. site yield nothing, which is too bizarre to be believed. With all the (largely internet-based) discussion of ecological footprints, I thought this info would be everywhere. Suggestions?
posted by sarahkeebs to Science & Nature (12 answers total) 6 users marked this as a favorite
You could presumably find, say, the amount of land area dedicated to agriculture in a state/country/region, and the gross agricultural output of that region. Those seem like numbers that people frequently track. CIA World Factbook, maybe?
posted by hattifattener at 11:19 PM on November 27, 2007

You can usually find the yields per acre of typical crops in typical climate zones, which you could probably then correlate with how much an average person consumes. Not sure you want to go to that much trouble, but, for example here's a chart of yields here in the States (pdf).

On this random informational site, we learn that a single bushel of wheat yields "A bushel of wheat yields 42 commercial loaves of white bread (one-and-a-half pound loaves). A bushel of wheat makes about 90 one-pound loaves of whole wheat bread."

Trying to figure out meats will probably be harder, as you'll need to figure out how many acres of grain and silage is needed to support an animal, and what that animal's share of the acreage it lives on is, I guess. But you can probably fudge that if you're just looking for a guesstimate.
posted by maxwelton at 11:21 PM on November 27, 2007

Sorry, guess I had a long-winded way of saying the figures for agricultural production are readily available; farmers live and die by this stuff, and entire government agencies track it. So phrase your queries in terms of "grain needed for beef cattle" or "okra per acre" and then correlate that with either human nutritional requirements ("calories per day human") or as the ingredients for popular foods, like the bread example.
posted by maxwelton at 11:28 PM on November 27, 2007

For pasture acres and meat/dairy production, start with AUM.
posted by bricoleur at 5:20 AM on November 28, 2007

Best answer: One commonly-used estimate of the minimum amount of arable land to feed one person is 0.07 hectares. For example:

"The minimum amount of agricultural land necessary for sustainable food security, with a diversified diet similar to those of North America and Western Europe (hence including meat), is 0.5 of a hectare per person. This does not allow for any land degradation such as soil erosion, and it assumes adequate water supplies. Very few populous countries have more than an average of 0.25 of a hectare. It is realistic to suppose that the absolute minimum of arable land to support one person is a mere 0.07 of a hectare–and this assumes a largely vegetarian diet, no land degradation or water shortages, virtually no post-harvest waste, and farmers who know precisely when and how to plant, fertilize, irrigate, etc. [FAO, 1993]"
posted by sfenders at 5:20 AM on November 28, 2007

If you're interested in the maximum yield, you might look into the Biointensive method. This book, by John Jeavons, claims that less than half an acre (~ 0.2 hectares) can support a family of four, or about 0.05 hectares/person, which is lower still than the lower of sfenders' figures.
posted by harmfulray at 7:48 AM on November 28, 2007

These are from speech notes from a guy named Jason Bradford, to a Rotary group in northern California. I don't know where he got them. The presentation used to be online here, but the link is broken, so I don't know where it is now.

Each person needs --
vegan food -- 3000 sq. ft.
a few eggs/week -- 3,500 sq. ft.
one chicken/week -- 24,300 sq. ft.
one cow/year -- 67,300 sq. ft.
posted by salvia at 9:51 AM on November 28, 2007

I am told that the plant with the highest calories to land ratio is the potato. And that one acre of potatoes will feed one man for one year. You'd still need vitamins, and protein, etc. It's not a complete diet.

But you could eat.

Check out survivalist literature. There are several articles (don't have an address off-hand) on "How to survive after the GREAT DISASTER"
posted by davereed at 9:56 AM on November 28, 2007

Yeah, following up on harmfulray, John Jeavons & Jason Bradford live(d) in the same town and I think may work together some. Though the numbers are different (0.05 ha = 5382 sq. ft.).
posted by salvia at 9:56 AM on November 28, 2007

To put the measurements in ye olde terms, an acre is 43,560 sq. ft., or a chunk of land a little more than 200 feet on a side. A football field is very roughly about an acre.
posted by maxwelton at 11:11 AM on November 28, 2007

Also, do you care about what sort of cultivation techniques are possible? Bradford points out that if you exclude tractors but do want to use mechanical cultivation, you'll need land to provide feed for the horses that pull the tractors.
posted by salvia at 11:15 AM on November 28, 2007

Another variable is going to be the quality of the land; an acre of hill farm will be different from an acre of polytunnels or cornfield, even if they're all in sight of one another. Then there's the extent to which you do or don't internalise your externalities - does that cornfield need artificial fertiliser? Is it a silly question to ask what's going into the polytunnels? I think the 'minimum' figures quoted tend to be for efficiently intensively worked land, assumed to be flat and neither soggy* nor blowing away. Since most agricultural land probably doesn't meet all these criteria, it would seem to be a somewhat unanswerable question, although I suspect there'd be a fair few PhD theses available to anyone who wanted to try hard enough.

[* except rice paddies that get flooded. And fish farms, I suppose.]
posted by Lebannen at 12:58 PM on November 28, 2007

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