Reader Jonathan H asked:
"Is corn ahead of potatoes for total calories?I've heard the claim that potatoes are the only crop that can feed a family of 4 from an acre of ground. Is this accurate?"
First, lets look at modern yields of potatoes and corn and then guestimate what might be likely under post-Apocalypse conditions.
Starting with virus-free seed potatoes, irrigating and fertilizing with 200 pounds of Nitrogen per acre, good weed and insect control, yields of 40,000 pounds of potatoes are very possible. Many of those will be too big or two small or too knobby to be salable but that is not a concern if you are just trying to fill your belly.
If you choose "high specific gravity" varieties then 15% of that weight (6000 pounds). If an adult needs 2500 Calories a day, then 40,000 lbs of potatoes will feed 4 adults for 1,200 days. If you can find fuel to cook them.
Modern yields of hybrid corn in the Corn Belt can easily produce 200 bushels/acre without irrigation. They require the same 200 pounds of Nitrogen, weed control and so on. In my experience, corn is more forgiving regarding insects and weeds than potatoes.
A bushel of corn weighs 56 pounds and 50 pounds are a guess at the digestible portion. 50 pounds/bushel * 200 bushels =10,000 pounds or 2000 days feeding a family of four adults.
Pre-fertilizer/pre-hybrid corn farmers were happy to get 40 bu/acre but even a little bit of fertilizer and stress-tolerant hybrids could hit 80 or 100 bu/acre.
Potato yields are likely to sag more as they are sensitive to the soil drying out, virus, insects and weeds. Let's guess 10,000 pounds/acre as an achievable target.
Of the two choices, potatoes come closer meeting a human's nutritional needs. It seems likely that families would supplement with greens, beans, dairy and whatever meat they can harvest.
Coming back to your question: "Is it true?", it depends on how restrictively you want to interpret the question. I think both have a place in the p-A garden. The corn is more resilient to less-than-optimal conditions and stores better while the potatoes can help avoid diet fatigue and have vitamin C.
The smart money would probably plant a quarter acre patch of each (35 paces square).
Regarding the specific claim regarding potatoes being the only... That claim is usually made to explain the population over-shoot problem in Ireland and the resulting famine in 1847-49. Ireland has reliable rainfall making it potato (and Late-blight) friendly and is cool making it unfriendly to corn. In the context of the crops widely available in Ireland in 1847, the statement is 100% true. In the wider context it is not.