From Schaeffers Trading Floor blog:
As Nick noted earlier, Potash Corp. of Saskatchewan (POT) was targeted by a wave of put buying on Monday. During the course of the session, option traders on the International Securities Exchange (ISE) bought to open 1,382 puts, compared to 132 calls. 
Yesterday's bearish bias stands in contrast to recent activity on the ISE, where POT has garnered a 10-day call/put volume ratio of 1.44. However, short-term option players are firmly aligned in the skeptics' camp, as the stock's Schaeffer's put/call open interest ratio (SOIR) checks in at 1.26, just 1 percentage point from a new 52-week high....MORE