Choked off shipping in the Strait of Hormuz isn't just grinding oil tankers to a halt. The Iran war is creating a one-two punch for the world's fertilizer supply, blocking both the export and one of its critical ingredients from leaving the Persian Gulf.

Nearly half of the world's traded urea, the most widely used nitrogen-based fertilizer, comes from the Gulf. As does one-fifth of the world's liquified natural gas (LNG).

A quick chemistry refresher: the century-old Haber-Bosch process combines nitrogen from the air with...