NEW ORLEANS, Oct. 14 -- One ship carrying 30,000 tonnes of Belarusian fertilizer was due at the Port of New Orleans on Wednesday, according to ship-tracking data from Kpler, the first such cargo to reach the United States in four years, and it is small enough that the signal matters more than the tonnage.

The cargo is a test of a deal, not a supply line. Washington lifted sanctions on the main Belarusian potash producers in March, after Minsk released 250 political prisoners under a US-brokered agreement, Al Jazeera reported. In September, US envoy John Coale announced a further agreement for 25 releases in exchange for more sanctions relief. President Donald Trump has said he is working on a larger purchase at prices "substantially less...