BEIJING, Oct 13 (Reuters) - China’s soybean imports in September fell 30% from the previous year, customs data showed on Wednesday, as poor crush margins curbed demand. China, the world’s top buyer of soybeans, brought in 6.88 million tonnes of the oilseed in September, down from 9.79 million tonnes last year, General Administration of Customs data showed. Chinese crushers stepped up purchases of soybeans earlier this year in anticipation of strong demand from the country’s fast recovering pig herd. Demand started to weaken, however, as plunging hog margins pressured crush margins. (Reporting by Hallie Gu and Shivani Singh; Editing by Christian Schmollinger)