If you took a quick glance at today's market, you might think nothing much really happened. The S&P 500 Index (^GSPC -0.46%) gained less than a single point, for crying out loud! Honestly, how much can really transpire on a day when stocks move less than 0.1%? It turns out that quite a lot can transpire, as evidenced by today's three biggest S&P losers, all of which swung violently lower on major news.

The most pronounced decliner of the day was agricultural chemicals player Mosaic (MOS -0.69%), which saw shares crater 17.7% as global markets learned of an impending and previously unexpected glut of potash supply. The supply of potash, a core ingredient in fertilizer, is largely controlled by a Russian cartel. Today, one of the two cartel members, Uralkali, announced that it's going solo; it plans on massively boosting production next year, resulting in a downward push on prices. Sometimes cartels can go rogue, apparently.

Secondly, Xylem (XYL -0.05%) shares plummeted 10.3%, as the water treatment company reported disappointing earnings and a weak forecast for the year. The demand for water treatment plunged the most on record, and profits took a nearly 50% hit in the quarter. The company blamed a weak economic environment in Europe and slumping U.S. industrial demand for the anemic results.

Finally, designer accessories behemoth Coach (TPR -1.60%) shed 7.9% after reporting a weak quarterly report of its own. Same-store sales of locations open at least a year, an important metric in retail, fell 1.7% in North America. Just in case shareholders were still holding any bullish delusions, management was sure to warn Wall Street not to expect better business next year. Oh, and two major executives are leaving after getting stiffed for the CEO job, as the company transitions to new top-level management.