The key is getting acreage planted. Weather delayed this, so as soon as investors learn whether the projected corn planting (97 million acres) is actually planted there's going to be some trepidation with fertilizer stocks.
With the weather there could be two possibilities. The planting could be delayed too long or it could get washed away, requiring replanting.
A delay could mean that farmers switch to a hybrid that has lower yields, increasing corn prices so that farmers are more likely to plant corn (which uses more N.) Farmers have traditionally used less N with late plantings, but from research I've read this may be based on tradition & not facts because results from reducing N are inconclusive & this reduction has the potential to reduce yields. So investors may be thinking of traditional fertilizer applications & may not know that fertilizer use is likely to increase due to use of starter fertilizer.
Of course washing away of a recently planted crop would result in replanting at a later date, so you would have the same delayed planting scenario. Also, starter fertilizer would leach out / wash away so it would have to reapplied.
With cool, wet weather farmers are more likely to use starter fertilizer because N & P aren't released from the soil so more needs to be applied. The damp ground can lead to compacting as well, in which case starter fertilizer also provides a benefit. I think CF mentioned that they had prepared for this by moving the appropriate fertilizer into growing regions. Although P is usually applied more heavily because it's associated with seed germination, I've seen some recent studies that indicate higher N will result in higher yields (higher P tapers off yields more quickly), so farmers may start to change in response to this information. In any event, CF sounded like they had a handle on this.