Potash group have learned the hard way the risk of riling customers.
When tumbling crop values squeezed farm budgets, PotashCorp and its kin, rather than lowering prices, dared growers to go without potassium.
So farmers did just that. They called the industry's bluff by engaging in a global buyers' strike.
Now - two months after PotashCorp warned that North American sales of potash had "ground to a virtual halt" - the Canadian group has said that Chinese buyers were dragging its heels, while Europe's K+S has warned of "extraordinarily weak" takings.
And growers' persistence has been rewarded. K+S is implementing potash discounts and, in taking a poke at "unsustainable" global prices, signalled that is expects rivals to follow suit.
What's worse for the fertilizer industry is that it looks like farmers may be in the driving seat for some while yet.
Potash groups have been banking on a revival in demand starting later this year. PotashCorp has forecast a rise of up to one-third in shipments in 2010 as potash in both warehouse and soil is replaced.
But there is reason to think that neither stimulus will live up to the Canadians' billing.
There is no sign yet of the kind of squeeze in the potash pipeline which could force prices back up. Indeed, producers' inventories, at 3.5m tonnes and rising, are at roughly twice their five-year average.
Meanwhile, there's a chance that farmers may get used to the idea of going light on potash. Crop yields are expected lower in most big producing countries this season, but not disastrously so.
While that doesn't mean growers will forever say "no" to potash, it may well mean they ask more questions about "how much". Potash use can remain depressed for years, as Standard & Poor's, the ratings agency, noted.
Such softness would be unlikely to blow a really damaging hole in a potash industry which has plenty else going for it, such as fresh markets in developing countries.
But it should teach fertilizer groups a lesson in the importance of treating their customers fairly.