Relations between Washington and Beijing are at their lowest in decades amid disputes over trade, technology, human rights and China's increasingly aggressive approach toward its territorial claims involving self-governing Taiwan and the South China Sea. Jason Lee | Reuters BEIJING — China's ambassador to the U.S., Xie Feng, has blamed U.S. tariffs and export controls for a drop in trade between the two countries. That's according to a speech he gave via video on Tuesday at Forbes' U.S.-China Business Forum in New York, published online by the Chinese Embassy in the U.S. China-U.S. trade fell by 14.5% in the first…