Soybean futures plunged to their lowest levels in more than a decade last week amid renewed negativity about a trade deal with China.

News of a new round of tariffs imposed on Chinese imports weighed on crop prices all week as CBOT July soybean futures sank to a low of $8.06-1/2 per bushel on May 9, the lowest for the most-active contract since Dec. 10, 2008, and almost $2 per bushel below this time last year.

Prices could head even lower if the trade war lingers, said Chad Hart, Iowa State University crop...