This, also US agricultural exports play a major role in US imperialism. Michael Hudson's talks on the subject are extremely enlightening- this one, on the broader "super imperialism" (recently bought his book on the subject, yet to delve in) and this one on the subject of the World Bank and US agricultural imperialism in particular.

The TL,DR is that the US heavily discourages agricultural self-sufficiency across the global south, and through this weaponizes/orchestrates famines across the world as one weapon of its empire.

Are there even many individual farmers in USA? From what i read it's more of a agricorpos running everything.

They better start planting oil palms trees

That's a good point, I imagine SWIFT gave the US a huge advantage in trade while other countries likely had to use heuristics.

Probably something like the smaller producers sold locally, governing their prices in part by what bigger producers set. Meanwhile, large producers could likely pay for the price discovery, individually or in a group, or they had many contacts which allowed them to have an idea of what would be fair. But it was likely the US was stealing quite a lot as middlemen, which can now be at least atenuated somewhat by having many people trading directly and perhaps even more "state help" to figure out good prices long term.

I would be interested in understanding this better as well, and nice to see that the new system is already being used. Whoever is not using the new system yet will likely do the math to see how good it will be for them.

Edit to add another point: Large producers would likely buy smaller local producers' production as well in case the export price was good, so the smaller producers would increase their prices when they knew the bigger producers were buying a lot.

Basically, since transactions were done using SWIFT, the US companies had a lot of visibility into who was selling what and for how much. This allowed farmers to have a good idea of what crops were in demand and how much to plant for the season. Now that transactions are being increasingly done outside SWIFT, they're opaque to the west making it much harder to predict what demand is like.

the process of determining the price of a commodity in the marketplace through the interactions of buyers and sellers. in this case farmers are trying to forecast what the price will be after the growing season

Very possible, this also means that a lot of the narrative in the west regarding slump of demand in China might not be an indication of Chinese economy slowing down, but rather the fact that China is not sourcing stuff from the west anymore.

It's likely, specially as from what I hear China was able to sell steel in Brazil cheaper than the local production too, so something likely changed/improved in China recently. It could be, at least in part, due to less internal demand, but cutting off the middlemen might have helped too.