Colonial Lowcountry landowners experimented with cash crops ranging from tea to silkworms. African slaves brought knowledge of rice cultivation, which plantation owners cultivated and developed as a successful commodity crop by 1700. With the coerced help of African slaves from the Caribbean, Eliza Lucas, daughter of plantation owner George Lucas, learned how to raise and use indigo in the Lowcountry in 1747. Supported with subsidies from Britain, indigo was a leading export by 1750. Those and naval stores were exported in an extremely profitable shipping industry.

African slaves had great knowledge of the cultivation of what product?