Part 3 · Subsistence First
Calorie and Yield Accounting
Bushels to pounds to calories to people. The four conversions that turn a harvest into an answer, worked once by hand so you can run it on your own ground.
A yield figure on its own answers nothing. Forty pounds of wheat is not food until you know how many calories it holds, how much seed must go back in the ground, how many people those calories feed for how long, and how many hours it cost to grow. This lesson is the arithmetic that connects the four, worked once in public so you can run it on your own plot and trust your own number more than this page.
Start from people, not from plants. The farm's own engine is built to work backward: it takes a household's daily calorie need, computes what must grow, and only then asks what land and labour that takes. The rest of this lesson is that calculation with the numbers shown.
The four conversions
Area. One acre is 43,560 square feet. The engine states its yields per 1,000 square feet, so to reach an acre multiply by 43.56.
Bushels to pounds. A bushel is a volume measure, so its weight depends on the crop. For wheat the planning constant used across this project is 60 pounds to the bushel, from the strike-logistics note that puts 50 bushels an acre at 3,000 pounds. Twenty nine bushels an acre is therefore 1,740 pounds.
Pounds to calories. The engine carries a calorie value per pound for all 65 of its crops. Winter wheat is 1,550 kilocalories per pound, fava beans 1,310, potatoes 350, sunflower seed 560, hazelnut 1,750. These numbers, the protein and fat grams per pound, the yields, and the labour hours are all in the crop file, and you should open it and read the row for whatever you plan to grow.
Calories to people. The adult requirement is about 2,200 kilocalories a day, 803,000 a year. Divide your annual calories by that and you have person-years of food before storage losses.
A worked acre
Take 1,000 square feet of winter wheat on loam, the engine's middle soil.
- Yield: 40 pounds.
- Seed reserve: 6 percent held back, so 37.6 pounds are eatable.
- Calories: 37.6 times 1,550 is 58,280 kilocalories.
- People: 58,280 divided by 2,200 is 26.5 person-days.
- Storage: dried grain loses 3 percent, so call it 56,500 kilocalories eaten.
- Labour: the engine's labour hours, plant 2, maintain 1, harvest 3, process 4, total 10 hours per 1,000 square feet.
Scale that to an acre and the yield is 40 times 43.56, or 1,742 pounds, about 29 bushels. Subtract the seed reserve and you have 1,637 pounds eatable, or 2.54 million kilocalories, or 3.2 person-years. One acre of wheat on loam, by this engine, holds about three people for a year on calories alone.
Calories per hour
The farm is usually shorter of hours than of land, so the number that decides which staple to grow is calories per labour hour. The model engine's demo output ranks the staples this way: wheat at about 71,100 kilocalories an hour, potato at about 49,300, fava at about 42,600, and olive at about 8,800.
Read the ranking as well as the top line. Wheat wins because it is low-labour and calorie-dense. It also carries little protein and almost no fat. The olive finishes last on calories per hour, and it is the crop that supplies the fat a wheat diet cannot. A household that picks its crops by calories per hour alone will grow wheat, eat it, and slowly starve of fat. This is opportunity cost in the field: the crop that wins one metric loses another, and the household chooses which scarce thing it is buying.
The four standards
Every carrying-capacity number is meaningless until it names the standard it is measuring against. The curriculum fixes four: survival calories, adequate nutrition, a healthy diversified diet, and a surplus-producing household. One plot can meet the first and fail the second. The next lesson shows that it can pass calories and protein and still fail, badly, on fat.
Exercise
Compute your own acre
Choose the staple you actually intend to grow and find its row in the crop file. Write down its calories per pound, its yield per 1,000 square feet on your soil, its seed reserve, and its labour hours. Then compute, in order: eatable pounds per 1,000 square feet, calories, person-days at 2,200 a day, person-years per acre, and calories per labour hour. State every assumption next to the number, including the soil type and the storage loss you assumed. The point of the exercise is the stated assumptions, not the final figure.
Fieldwork
Weigh your own bushel
Before the grain goes into the store, fill a bucket of known volume with your cleaned crop and weigh it. Weigh the seed you are holding back, too, and note the difference. Use your own measured weight per volume, rather than the table's 60 pounds a bushel, to convert your harvest into pounds, then into calories, then into person-days. Bring back three numbers on one sheet: pounds harvested, pounds kept for seed, and days of food after storage loss.
Failure mode
A single productivity number is the most common lie in farming, and it is usually told by accident. A yield per acre that counts seed as food, ignores storage loss, or reports the weight of a crop with a high water content against one that keeps dry, is not comparable to anything. Fix the unit, fix the standard, fix the losses, then compare. If you cannot state your assumptions, you do not yet have a number.
