Add one more critical shortage to the world's swollen list. Countries for months have been hoarding fertilizer - and now they are weaponizing it, making sales in return for geopolitical favors. Last July, China's National Development and Reform Commission stopped major companies from exporting fertilizer. In September, Beijing imposed a prohibition on exports of phosphates, a primary fertilizer ingredient, until at least the middle of this year. In October, Chinese officials added inspection requirements to aid enforcement of the bans. The moves were a reaction to rising prices in China and elsewhere. China's fertilizer bans created shortages. The country's traditional...