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: So far today, shares of Terra Nitrogen (NYSE: TNH) have swung from as high as an 8% gain, to as low as a 12% loss in comparison to yesterday's closing price. Don't you just love rollercoasters?

So what: The fertilizer producer reported earnings last night, announcing earnings per "common unit" of $3.95, a 78% improvement over last year's Q2. The limited partnership immediately announced it will pay out $3.75 of that as cash distributions to its owners.

Now what: Terra's bumper crop of Q2 earnings has the stock selling for about 4.2 times trailing earnings today -- a sizeable discount to the P/Es at non-limited partnership-rivals CF Industries (NYSE: CF) and Agrium (NYSE: AGU). Wall Street doesn't say how fast it expects the company to grow earnings, but right now, today, it looks pretty cheap to me.

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