General discussion, page-758

You will see a drop in phosphate demand for 1 year and they can rely on residual phosphate in the ground from previous years application, but after 2 years farmers need to re-apply or they risk crop failure. Many farmers need to take advantage of moisture / temperature windows and chemical fertilizers are what gets many of them over the line.

Graziers can just not apply for a few years without much impact if they have good soil, but most graziers don't use much so don't notice the price fluctuations as much.