If successful, the $8.74 billion deal would be one of the largest mining deals in recent years, according to The Wall Street Journal.
Potash Corp. is a Canadian fertilizer producer and Germany-based K+S is Europe's largest potash supplier. Potash is a key ingredient in fertilizers.
However, K+S is likely to reject the offer as too low, the Journal added.
This bid is the latest move by a North American company on a European rival, as U.S. and Canadian firms see low interest rates and a weak euro as opportunities to pursue new growth, the Financial Times reports.
On Friday, shares of Potash are slumping 2.32% to $31.15.
Separately, TheStreet Ratings team rates POTASH CORP SASK INC as a Hold with a ratings score of C+. TheStreet Ratings Team has this to say about their recommendation:
"We rate POTASH CORP SASK INC (POT) a HOLD. The primary factors that have impacted our rating are mixed, some indicating strength, some showing weaknesses, with little evidence to justify the expectation of either a positive or negative performance for this stock relative to most other stocks. The company's strengths can be seen in multiple areas, such as its increase in net income, expanding profit margins and growth in earnings per share. However, as a counter to these strengths, we also find weaknesses including weak operating cash flow and a generally disappointing performance in the stock itself."