Where is Brazil growing that soy? In their vast and ample prairies? (hint: the answer to the second question is 'no')
> So we can't move food where it needs to be, so that should increase reserves being held.
This parallels a problem we have in cluster management - if load increases and you spin up new servers as a response (increasing capacity), then depending on how those servers work they might actually increase load while trying to spool up. You then have to be careful you don't create a feedback loop where spinning up servers triggers spinning up more servers.
If you can't get food into the ports, then stockpiling it means bringing more food in through those same ports. Which makes getting food (and other supplies) slower, which means you increase your stockpiles, which means more shipments having trouble getting into port...
Often the right answer is to raise the low water mark, which means that the status quo is maintained until the next lull, when you hold on to some of your excess capacity instead of letting it go, and to refine your boundary conditions to react a little bit sooner, and/or a little less aggressively (ie, do less but do it sooner).
https://pt.wikipedia.org/wiki/Produ%C3%A7%C3%A3o_de_soja_no_...
https://pt.wikipedia.org/wiki/Produ%C3%A7%C3%A3o_de_soja_no_...
Of course it's 'no'. It is mostly produced on the savanna and semi-arid areas.