One of the traders said Chinese buyers had booked 15 cargoes. "These deals were done last night after Argentina's decision on export tax," said one of the traders, declining to be identified as they were not authorised to speak with media. China, the world's biggest buyer of soybeans, has yet to purchase any U.S. soybean cargoes from its autumn harvest, traders have said. By that time in previous years, traders said, China would have bought 12-13 million tons from the U.S. for Sept-Nov shipment. Argentina typically imposes a 26% export tax on soybeans.