PotashCorp (NYSE:POT) is turning out to be among the worst performers of 2015. The stock has lost roughly 6% since the fertilizer giant reported its third-quarter numbers earlier this month, taking its year-to-date losses to a staggering 41% as of this writing. That hugely lags the broader market, as well as peer stocks Mosaic (NYSE:MOS) and Agrium.

POT Chart

POT data by YCharts

While all three companies operate in similar business conditions, PotashCorp loses out because of its greater exposure to its namesake nutrient, potash, the market for which is battling several headwinds at the moment. Comparatively, Mosaic is more focused on phosphates, and Agrium has a diversified portfolio that includes seeds and crop protection products.

However, a challenging potash market isn't the only concern, as PotashCorp's third-quarter earnings report revealed. The company downgraded its full-year earnings outlook, but there's a lot more going that could hurt its revenues and profits even further. The slideshow below highlights three such worrisome trends that you must know about. 

Neha Chamaria has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.