The beginning of agrarian life saw the beginning of cities. Cities gave rise to human specialists. Specialisation gave rise to technology. To sustain technology we need to maintain cities and the specialist within. As a first run, let’s ensure all are fed.
In China’s Zhanli province, the populace on average use 0.1 hectares of farmland per person. The subsistence line set by the United Nations is 0.05 hectares per family. The people of Zhanli are capable farmers and get enough from one annual crop to provide for nearly two years of food. Land not used for growing rice is used for other crops or livestock.
Typically 3 to 5 tons of rice can be grown per hectare. The projected maximum production is about 6.7 tons per hectare. We will use 4 tons for our calculations. At 17 kJ/g this gives 6.8e10 joules hectare. A person needs about 3.8e9 joules per year of food energy. Thus, assuming a 100% efficient conversion, a person needs 0.055 hectares (similar to the UN’s value).
A family of 4 needs 0.2 hectares. A hectare is only 100 by 100 metres. Assume a family maintains one hectare of land. This means they can provide for nearly 16 specialists. Or, at least they can provide for the specialist’s food requirements. However, once the specialists consume more energy than is derived from food, whether making urns or programming computers, their energy demands increase. We’ll look at this next time.
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