Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of fertilizer producer Terra Nitrogen (NYSE: TNH) ended Monday down 10%, hurt by a USDA report showing corn stockpiles nearly 20% higher than they had been previously estimated.

So what: On the one hand, having more corn than we thought we had is bad news for farmers (and the folks who sell them fertilizer). It means we may not need to grow as much, to keep the silos full, as would otherwise have been necessary. Compounding the damage, plentiful corn stockpiles tend to depress grain prices -- draining money from farmers' pockets and reducing their ability to spend money on fertilizer.

Now what: Now for the good news: These things tend to happen in cycles. If grain prices fall in response to the USDA report, these cheaper prices will logically increase demand for corn, and eventually increase prices as farmers struggle to meet the new demand. This will -- again, eventually -- be good news for fertilizer stocks. With Terra Nitrogen shares currently priced at less than 7 times trailing earnings, a buying on the dip today could pay off for Fools able to look out past the end of just this current demand cycle.

Want to learn more about Terra Nitrogen? Add it to your Fool Watchlist.