Potatoes yield about 2.8-5.25 million kcal per acre and sweet potatoes 2.3-4.7 million, the highest of any crop in the caloric guide, but they are mostly water: supplying 30% of a community of 100’s calories from potatoes means storing about 87,600 lb, nearly 44 tons. Turnips store well and feed people and animals, but the guide gives no turnip yield, so they cannot be counted in the calorie plan from it.
Part of Caloric Budget for a Community
Root crops are the potatoes, sweet potatoes, turnips and similar plants whose swollen underground parts supply calories and can be stored through winter in cool cellars.
High Calories Per Acre, Heavy To Store
The caloric guide’s sample plan allots 10-15 acres to roots: potatoes, sweet potatoes and turnips. Its figures for the first two are in the table.
| Crop | Yield (lb/acre) | kcal per lb | kcal per acre (million) |
|---|---|---|---|
| Potatoes | 8,000-15,000 | 350 | 2.8-5.25 |
| Sweet potatoes | 6,000-12,000 | 390 | 2.3-4.7 |
Turnips do not appear in the guide’s yield table. Raw turnip is about 28 kcal per 100 g, or about 127 kcal per lb (recalled food-composition value), which is under half the energy of a potato by weight; a yield per acre is not given, so no calories-per-acre figure can be stated.
Worked Example: What Does A Potato Share Weigh?
The guide recommends that no single crop exceed 30% of total calories.
- 30% of 102.2 million kcal = 30.66 million kcal from potatoes.
- At 350 kcal per lb: 30,660,000 ÷ 350 = 87,600 lb.
- In short tons: 87,600 ÷ 2,000 = 43.8 tons, nearly 44.
- The same share in sweet potatoes at 390 kcal per lb: 30,660,000 ÷ 390 = 78,600 lb, 39.3 tons.
This is the weight to store through winter, before any spoilage margin, and it fixes the cellar size (Root Cellars).
What You Need
- Seed potatoes or slips, saved from your own crop, with a variety mix to limit disease risk (Pest & Disease Management for Crops)
- Cool, dark, frost-free storage with ventilation (Root Cellars, Root Crop Role)
- A plan for the bulk: carts, bins and labour at harvest
- A rotation, since potatoes share pests and diseases with tomatoes and other members of their plant family (Crop Families and Rotation Logic)
Method: Plan Roots
Step 1: Fix the calorie share each root will supply, at or below 30% for any one. Step 2: Convert it to pounds, as above, and to acres using the middle of the yield range. Step 3: Size the cellar for the pounds, with the spoilage margin set by your record. Step 4: Use turnips for volume, stock feed and variety, not as the main calorie source.
Common Mistakes
- Leaning on one root variety. A single disease can take the whole crop.
- Storing damaged tubers with sound ones. Rot spreads through the pile.
- Ignoring the water. Roots weigh a lot per calorie, so transport and storage labour is large.
Safety
Green or sprouting potatoes are toxic
Potato skin that has turned green in the light, and sprouts, contain solanine, a poison. Store potatoes in the dark, cut away green parts and sprouts generously, and do not feed badly greened tubers to children or animals. This is recalled food-safety knowledge, not a figure from the caloric guide.
What’s Next
- Learn next: Legumes and Oil Crops — protein and fat to go with the roots
- Combine with: Winter Calorie Gap Planning — where stored roots are used