A community’s land plan needs a buffer for crop failure, pests and seed saving, and the caloric guide gives four rules: plant 20% more than calculated, hold back 10-15% of each harvest as seed, keep one year of emergency grain, and let no single crop supply more than 30% of calories. These overlap, and the arithmetic shows that planting 20% extra leaves only about 2-8% above need once seed is set aside.
Part of Caloric Budget for a Community
A crop buffer is the surplus acreage, stored food and crop diversity a community keeps so that drought, disease, pests or a poor year do not cause hunger.
Four Rules, Each Doing A Different Job
The caloric guide’s safety margins are: always plant 20% more than calculations suggest; keep one year of emergency grain in sealed storage if possible; diversify so that no crop is more than 30% of total calories; and track actual yields and adjust annually. Earlier in the guide the land doubling for crop failure, seed saving (10-15% of the harvest), fallow and animal feed is described as a 100% buffer. The pieces are not independent, so it helps to see what each does.
Worked Example: Does 20% Extra Cover The Seed?
- Planting 20% more than the need gives a harvest of 1.20 times the need, before any loss.
- Seed saving takes 10-15% of the harvest: 1.20 × 0.85 = 1.02 and 1.20 × 0.90 = 1.08 are left as food. So after seed, the 20% extra is only 2% to 8% above need.
- The harvest can fall short by how much before food runs out? With 20% extra and no seed saving, a loss of 1 − 1 ÷ 1.2 = 16.7% still meets need. After seed saving, the tolerable loss is only 1 − 1 ÷ 1.02 = 2% up to 1 − 1 ÷ 1.08 = 7.4%.
- So the 20% rule gives little protection by itself once the seed is counted; the protection must come from the stored year of grain and from crop diversity.
Worked Example: The 30% Cap
- If one crop supplies 30% of calories and fails completely, 70% remains.
- 70% of the 2,800 kcal community average is 0.70 × 2,800 = 1,960 kcal per person per day.
- That is below the caloric guide’s light-labour band of 2,200-2,400 for an adult, and well below its moderate and heavy bands, so a total failure of a 30% crop is a real shortage, not a reduction in comfort. The cap limits the damage to about 30%; it does not remove it, and stored food and animals have to carry the difference (Winter Calorie Gap Planning).
The phrase “one year of emergency grain” is ambiguous: the guide does not say whether it means a year of all calories or a year of grain only. A year of all calories for 100 people is 102.2 million kcal, which is about 62,000 lb of corn at 1,650 kcal per lb (102.2 million ÷ 1,650 = 61,900). Decide which meaning you are using before building the store.
What You Need
- Yield records from every plot, each year
- Sealed, dry storage (Grain Storage, Granary Design)
- A pest plan with handpicking, companion planting, rotation and biological control (Pest & Disease Management for Crops)
- Drought preparation (Drought Resilience)
- A seed bank with open-pollinated seed (Seed Bank Management)
Method: Build The Buffer
Step 1: Compute the need and the crop acres. Step 2: Add the planting margin and subtract the seed share to see what is left. Step 3: Set the crop shares so that none is above 30%. Step 4: Build a store sized to the meaning of “emergency grain” you chose. Step 5: Each year, replace the guess with measured yields.
Common Mistakes
- Counting the 20% as spare. Much of it is the seed.
- One crop at 60%. A single blight then removes more than half the calories.
- A store with no rotation. Old grain spoils; use the oldest first (FIFO Rotation).
What’s Next
- Learn next: Seasonal Production Calendar — when the buffer is drawn on
- Combine with: Winter Calorie Gap Planning — the store that the buffer feeds