BEIJING, Oct 20 (Reuters) - China's soybean imports from Brazil in September fell 18% from a year earlier, customs data showed on Wednesday, as poor crush margins limited demand.

The world's top buyer of soybeans brought in 5.936 million tonnes of the oilseed from Brazil last month, versus 7.25 million tonnes in the corresponding year-ago period, data from the General Administration of Customs showed.

Crushers stepped up purchases last year from top supplier Brazil as a fast recovering pig herd pushed up demand. But their buying has slowed in recent months, as falling hog prices hit margins.

China's hog margins remain in negative territory, despite a pick-up in the past week.

Soybean brought in by Chinese crushers is processed into feed ingredient for the livestock sector, and for use as cooking oil.

Imports from the United States stood at 169,439 tonnes, down from 1.17 million tonnes a year earlier, after hurricane Ida hit shipments by forcing the closure of some grains terminals on the U.S. Gulf Coast. (Reporting by Hallie Gu and Shivani Singh; Editing by Himani Sarkar)