In the annals of well-intentioned agricultural policy, few ideas have acquired the virtuosity halo of circular farming. The idea of returning organic waste back to the land, closing nutrient loops, and healing a degraded earth is all good vibes.
And as a policy, China has been implementing a version of this to address one of its most pressing agricultural challenges. Decades of intensive nitrogen fertilization have acidified swaths of the country’s croplands, particularly in the south. As a result, yields have been smaller, the soil chemistry destabilized, and if you measure for toxic metal the results have not been reassuring. The proposed fix: recycle animal manure back onto fields.
Makes sense. Manure raises soil pH and lowers acidity and it reduces the need for synthetic phosphate fertilizers. It’s the sort of policy idea that practically sells itself.
But in practice it doesn’t seem to be working.
The problem is cadmium, a heavy metal that’s been building up in rice grain, working its way into the food chain, and then quietly destroying the kidneys of people who eat enough of it. It gets into manure through the feed additives that are fed to animals in industrial pig and chicken operations. They are given mineral supplements to promote growth. The cadmium goes in one end of the animal and out the other, and then someone spreads it on a rice field. Right now, China permits higher levels of that contamination in feed additives than Europe does. Twice as high, in fact.
In a recently published study that focused on a dominant rice-producing area in China’s Hunan Province, more than 76% of rice samples already exceed China’s own food safety threshold for cadmium. That is not a future scenario. It’s now. And its particularly problematic given that this is the top rice-producing region in China, a country that produces about 30% of the globe’s rice.
The truth, though, is that this issue which seems contained to the agricultural system, is actually part of a bigger circularity problem in and of itself. Those same researchers who found high levels of cadmium in rice also tracked where it was coming from. Yes, they found it in manure, but also in fertilizers, irrigation water, and even the air. That latter part needs to be underlined. Cadmium particles, drifting down from nearby metal smelting plants concentrated in Hunan Province account for some 66% of what lands on the rice paddies. At the end of the day, the manure was responsible for just for 22% of the metal.
(smelters)
That points to a larger industrial circularity story at work. The cadmium goes into the smelter, into the air, onto the field, into the soil, into the rice, into the bodies of people. Until those emissions are cut, the amount of manure that can be safely spread is effectively capped. So the soil health benefits that circular agriculture might have promised remain out of reach. Not because the farming is wrong, but because of the air.
To be clear, none of this is a reason to abandon the manure-recycling approach. Soil acidification is real, its consequences are serious, and returning organic matter to degraded farmland remains valuable. The lesson here is that circular agriculture cannot work while the air above food fields delivers a steady supply of the very contaminant you are trying to manage.
Fixing the soil is an industrial policy problem, not one relegated to only the world of agriculture.