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Comment by rgmerk | Hacker News Reader

I remember reading part of a PhD thesis about the implications of “peak phosphate” more than a decade ago. (Not my area of expertise, but the guts of it weren’t particularly difficult to understand).

My takeaway (though not the author’s) was that it’s way down the list of things to worry about.

Basically, the cost of phosphate is such a miniscule component of the cost of food that it would make essentially no difference if we had to mine lower-grade sources of it.

Higher prices might also reduce the amount wasted as runoff, which also would reduce the environmental damage caused by fertiliser use, something we’re going to have to take more seriously at some point.

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Phosphate in soil is mostly in fixed, unavailable forms (like ferrous phosphate). Prolonged application of phosphate fertilizer would cause their accumulation. At that point, I think it would be worthwhile to look for ways to tap into that store, for example Phosphate Solubilizing Bacteria (PSBs), or plants genetically modified to perform the same function in their roots.

Phosphate removed from fields by erosion or in plant matter would have to be replaced at some point.

Just 10-20% of applied phosphate fertilizer is taken up by plants. The rest gets lost in these insoluble forms. So there's a lot of room for improvement here.

Perhaps I live under a rock, but phosphate is expensive. I was buying diammonium phosphate at $250 per ton a few years ago. Then it went to $340. Then COVID happened and it went to $600. Then the next year it was over $800. The ag supply company didn't even have enough cash to pay for a truck load. They've completely stopped carrying it now.

I'm sorry but you're saying a literal ton, over 2,000lbs, at $600 is expensive? I can't think of any material I can buy a ton of for $600.

yeah, lightly processed minerals are super cheap; dap sold as fertilizer is full of other crap because phosphate just fucking loves every polyvalent metal ion it ever laid its little orbitals on. fortunately because all that crap is insoluble it's pretty easy to filter out of an aqueous solution

a list of materials that cost less than US$600/tonne, aka 60¢/kg, near me at retail in the last few years:

- steel scrap (30¢)

- aluminum scrap (58¢) (this is what recyclers pay the cartoneros)

fine minerals for cosmetics, pottery, or foundry work:

- bentonite (28¢)

- mesh-80 calcite (45¢)

- mesh-200 calcite (20¢)

- dirty beach sand (6.2¢)

- tierra de Junín for aluminum casting (20¢)

- red clay (30¢)

- ball clay (30¢)

- 200-mesh quartz flour (30¢)

- pure quartz sand (35¢)

- 200-mesh talc (40¢)

- baryta (46¢)

- magnetite (10¢)

- infusorial earth (40¢)

- calcined metakaolin (35¢)

construction binders:

- plaster of paris (30¢)

- slaked lime (11¢)

- portland cement (26¢)

aggregates for construction:

- clean construction sand (2¢)

- pumice (42¢)

- broken-rock aggregate for concrete (8¢)

- ungraded gravel for concrete (0.8¢)

- 6–20 mm gravel for concrete (1¢)

- quartz gravel aggregate for concrete (15¢)

landscaping materials:

- pure white marble pebbles (12¢)

- quartz gravel for landscaping (2.1¢ in minimum quantity 6 tonnes)

- ornamental 1-4 cm landscaping rocks (8¢)

- round 1–3 cm river rocks (9¢)

miscellaneous:

- gravel for fishtanks (19¢)

- water (0.06¢)

materials this cheap vary a lot in price depending on location, because most of the cost is shipping. diammonium phosphate around here is about US$1/kg

i hope this helps

Salt is about a third the cost. You can get a 1 ton pallet of salt, processed, bagged up and delivered to a business for far less than $600. It is amazing to see in action.

Yea. For other's reference: a tractor trailer can haul something like ~40 tons and costs ~$4k to go cross country, so shipping costs from mine to fertilizer processor to farm are already going to be in the general ballpark of $100/ton.

Mining, as I've known it, uses Haulpak trucks onsite that each carry > 110 tonnes.

They fill a train a day (at least), the trains being some 2.4 kilometers in length carrying some 29,000 tonnes that typically travel some 100km from minesite to coastal port.

Ship capacities are 380,000 to 400,000 tons deadweight and travel about the globe.

"Tractor trailors" (or two to three trailer road trains) as you're describing are used to bring food and supplies and general light goods too and from a minesite.

There are such things as economies of scale.

Fair enough, but the phosphorus has to be delivered to a farm (either before or after being combined into a fertilizer), and that's done with a truck, right? Are you arguing that the total transportation cost of the phosphorus that eventually gets it to the farm where its used is going to be much less $100/ton?

Separately, what term other than tractor trailer should I use to sound cool?

It highlights how much profit is made on repackaging things into smaller quantities for consumers. Mind you, in the US you have Target which a lot of people go to, because bulk buying is cheaper. We do the same, 5 kilo bags of rice instead of pound bags because we go through enough of it, it's less than half the price of buying pound bags individually.

But if you ever have a larger landscaping job to do, go to a wholesaler, they can deliver tons of materials at your doorstep for relatively cheap.

Landscaping materials? You can get things like sand and mulch for like $30/ton.

You just have to provide your own transportation.

Gravel, $20 a ton.

So for NPK fertilizer, I now know that nitrogen is manufactured cheaply with the haber-bosch process, and we've got a lot of phosphate available. Do we also have plenty of potassium around? i.e. enough to realistically never worry about "peak potassium".

Sea water contains huge amounts of potassium that is easy to extract.

The most abundant rocks also contain huge amounts of potassium, but which is expensive to extract.

Neither in nature nor in agriculture potassium is ever a limiting nutrient like nitrogen and phosphorus.

I have to object to the last sentence. I’ve gotten lots of soil tests from various locations in soil and greenhouse media where I need more nitrogen (almost always) and potassium (sometimes), but never phosphorus.

And I even live in one of the blue states with lower P in the soil.

https://pubs.usgs.gov/sir/2017/5118/sir20175118_element.php?...

There's a gardening channel on youtube I watch (RED Gardens) where the guy does all sorts of small scale experiments with organic gardening. He was a bit surprised to discover his soils have excess potassium, from the various organic materials he had been using (like wood chips for mulch; pot ash, right?) The soils were also sodium deficient, so he was thinking of spreading measured amounts of salt!

He also discovered commercial compost can be crap, since it hasn't broken down enough and soaks up nitrogen as it finishes its decomposition in the ground. So if your potatoes are struggling in something like that, slather on some urea and they'll perk (and green) right up.

if potassium was never a limiting nutrient it wouldn't be sold as a fertilizer at all, much less be one of the three primary fertilizer nutrients

You are right that I did not express that well, because as said it is true only in natural places, not in artificial cultures.

For modern cultivated lands potassium must be indeed used as a fertilizer, because much of what exists in the soil is removed by remaining in the plant parts that are harvested then transported elsewhere. Another part of the potassium may be washed away by intensive irrigation.

So the potassium that is taken away depending on the cultivation methods that are used must be replenished. However its abundance is such that this will never be a problem.

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