Potash Corporation of Saskatchewan Inc. (TSX:POT)(NYSE:POT) and Teck Resources Ltd. (TSX:TCK.B)(NYSE:TCK) have endured some tough times in recent years. Let's take a look at the two commodity giants to see if one deserves to be in your portfolio. Potash Corp. Potash Corp. is struggling with low fertilizer prices, heavy competition, and difficult conditions in key markets. Potash prices are trading at multi-year lows as the world's largest producers battle it out for market share. The war began in 2013 when miners in Belarus and Russia ended a cozy marketing relationship. So far the two companies have refused to kiss and make up, and there is little evidence the cartel will re-form in the near term. The spot price for potash prices initially fell from US$400 per tonne to about US$300 per tonne when the Russia-Belarus split was announced. Today potash is trading for close to US$240 per tonne.