I’m not sure this one - finite amount of minerals in soil - is the ultimate factor limiting biomass density on earth.

As for the “Swapping Children/Making Food,” check Manning’s Against the Grain.

Can you provide any figures regarding the ammounts of essential minerals available in soil/water versus those trapped in living tissue?
While it is scientifically true the more oxigen is trapped in living tissue the less it remains in atmosphere, that doesnt mean there isnt many times more free oxigen (2 tons/square meter) than in living things

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Also I could not find references regarding the “Swapping Children / Making Food” in ancient China.

As for farming systems, there is a constant amount of minerals and other elements on earth. In terms of energy, the energy exchange is net positive when energy is stored in carbon based lifeforms, of which a finite number can be sustained by the finite amount of minerals and other chemicals available to said organisms on the earth’s surface.

The more minerals that are locked up in animal bodies, the less there is in the soil. Overpopulation thus leads to poorer soil, causing die-off, and as the corpses decay, the minerals are returned to the soil. As you say, the amount is ultimately constant, but this is precisely why agriculture cannot be continued indefinately. Constant growth is simply not possible.

Having people astute enough (written history helps too) to figure out what was coming, before it arrived is one of the probable reasons for the longevity of Chinese civilisation. That and the fact regular flooding kills lots of people and deposits nutrient rich sediment on the many flood plains along the major rivers (plus the deltas). That and the almost continous warfare that helps reduce the population of soldiers and civilians alike, and is a feature of every agrarian civilisation.

As for farming systems, there is a constant amount of minerals and other elements on earth. In terms of energy, the energy exchange is net positive when energy is stored in carbon based lifeforms, of which a finite number can be sustained by the finite amount of minerals and other chemicals available to said organisms on the earth’s surface.

For the purposes of discussing China, the deserts mean that China depends on energy input, having sacrificed biodiversity long ago. To build up the soil again, they need the biodiversity back that did this for them before practicing agriculture. Since they couldn’t possibly know what was lost, they have little hope of shedding their energy dependency to support such a large population. Waiting for nature to take it’s course may take tens of thousands of years.

This is what Permaculture and Natural Farming seek to address. China and India may be too far gone to keep the coming population collapse graceful. I’d say the writing is on the wall on this one.

Theoretically, you could ‘close the loop’ on an agroecosystem’s nutrients(NPK, + micros), recycling everything that was excreted, composting the dead, etc. Whether or not it is worth the energetic cost of doing so, is another question.

Assuming a static population. If your population is growing, then the amount of nutrients being taken out is larger than the nutrients being returned. Otherwise, the population wouldn’t be growing.

Theoretically, you could ‘close the loop’ on an agroecosystem’s nutrients(NPK, + micros), recycling everything that was excreted, composting the dead, etc. Whether or not it is worth the energetic cost of doing so, is another question.

It is *not* theoretically possible to close the loop on energy production, due to the laws of thermodynamics and the trophic limitations imposed by those laws (as Jason mentioned in the article).

Good thing that sun continues to shine…

If the tree were the only thing growing, then the tree would absolutely diminish the system. The reason the tree doesn’t diminish a biosystem (life couldn’t exist otherwise) is that it is only a small part of the overall biodiversity. A biosystem can’t be simplified by energy input alone; nor can minerals be taken alone; nor can a small set of species be expected to remain stable (agriculture is unreliable, leading to desertification).