Germany Sees US as Vulnerable to Squeeze on Potash Supplies

German authorities seeking to map out US supply-chain vulnerabilities as a way to win leverage with President Donald Trump’s administration have identified a key pressure point: potash.

The US imports more than 90% of the key ingredient for agricultural fertilizer, leaving the world’s No. 1 economy highly reliant on global producers — above all Canada. Potash, a potassium-rich fertilizer made from underground deposits, would be among options for US allies should Trump further ratchet up trade and security threats, according to people familiar with the considerations.

The US president’s threats to seize Greenland, a Danish territory, stunned European leaders ...