Elemental sulfur is usually part of a multi year strategy. Not sure what pH potatoes need but we’ve had success using ATS 21-0-0. In fields with a starting pH of 8 and after 5 applications of 50lbs/ac across 5 weeks we’re down in the low 7s. There’s a lot of variables at play so it’s likely the ATS alone isn’t responsible for that dramatic of a shift, but it is one of the most acidifying salts you can use. Phosphoric acid is another option but more expensive and used at a lower rate.