Time for a thread about my new research topic: #nutrient flows!
I started looking at #nutrients and #agriculture a while ago and was appalled by the current situation of our agri-food system:
from a mathematical standpoint, if you want #sustainability, you need to bring back the same quantity of nutrients you extracted during harvest, right?
To grow food it's a little more subtle than that, but broadly, you want a circular system.
Do you know how far from circularity our food system is?
1/N
When you start looking into it, the dominant agricultural system is somewhat puzzling:
1. plants need fertilisers so we make them
- this costs a lot of energy and fossil fuels to make NH3 from atmospheric N2
- it required mining for phosphate rocks and potash
2. we eat some of the plants, give the other to animals
3. we eat the animals or something they produce (e.g. milk)
And then what happens to the nutrients?
Can you guess?
2/N
Then, nutrients are excreted in urine and feces:
- for animals, some is recovered as manure
- the rest is mixed with water and goes to water treatment plants
- there, we pay a lot of energy to convert the N to gaseous N2 and send it back to the atmosphere
- for P and K, it is slightly better, as a part is recovered in the sludge and used on parcels...
- but it has been contaminated by wastewater pollutants (including heavy metals)
Your standard linear, extractive system.
3/N
The whole system is actually an agri-food-excretion combination.
By treating them separately, we are creating a few (!) problems with the whole system:
a) We don't have unlimited energy, nor gas, to resynthesize the usable nitrogen we "destroy" (especially now)
b) Phosphorus and potash mines are finite resources and the current system is sending precious nutrients to the sea!
c) Nutrients not recovered in water treatment plants pollute water streams and coasts (ever heard of algal blooms?)
4/N
So how do we solve this?
Today we use around 100 Mt of N, and 40 Mt of P and K a year worldwide.
https://ourworldindata.org/grapher/fertilizer-use-nutrient?country=~OWID_WRL
We have very low efficiency for their application, though, so while African soil does not get enough nutrients, there is a large excess almost everywhere else.
Recovering human excreta (around 30 MtN, 3 MtP and 5 MtK), coupled with food scraps/waste reuse, better efficiency, and more plant-based diets, would go a long way towards making our food system more sustainable.
5/N
But how do we do that?
How do we move from a situation where we recover only a few percents of the nitrogen and barely half of the phosphorus, to something that get's close to 100%?
Can/should we move away from a combined sewer systems?
Is it compatible with a world where most of the population lives in dense urban areas? (recovering human excreta there is no small feat!)
What are the associated problems, costs, and benefits? Is it safe from a sanitary perspective?
6/N
Well, stay tuned, I'll discuss these points in the future ;)
I'll just finish here for now, and end this thread with a nice quote from Asimov: "[W]e may be able to substitute nuclear power for coal, and plastics for wood, and yeast for meat, and friendliness for isolation -- but for phosphorus there is neither substitute nor replacement".
7/7, the end!
@tfardet it is not a "supply-side" problem. A lot of crops are apparently grown to feed poultry and livestock. And a good portion of the edible crops are for sugar (and tobacco?). And the effect of it all gets twisted into "food scarcity for the poor", so as to justify increased fertilizer and #Biocide use and also #Deforestation. #VandanaShiva has been shouting hoarse on this for decades.
Avoiding meat and sugar consumption is bang-for-the-buck. For starters.
