How much cropland is required to feed one person for one year?
Walker, David. Energy, Plants and Man. Oxygraphics, 1992. (Page 133) says:
20 square meters (m2) is theoretically possible - just potatoes,
110 m2 if we assume production of the best potato crop ever,
300 - 400 m2 in practice, just potatoes.
The Vegan Society, www.vegansociety.com/environment/land (2009) says:
300 m2 if it's mostly potatoes,
700 m2 for a more varied vegan diet,
1400 m2 if a little milk or eggs are included.
Engleman et. al People in the Balance, Publ. Population Action International, Washington, DC, 31 pp. (2005) say:
700 m2 is the bare minimum for one person - vegetarian diet, no fertilizers.
700 m2 is the value commonly used by the United Nations Food and Agriculture
Organization.
Potatoes are the most productive crop per acre, and they are fairly nutritious
too.
At 700 m2, one football field (including the end zones and sidelines) could
support seven people.
Of course on Mars the sunlight is less than half as strong, and so you would
need twice as much land!