Taiwan, they started to grow tea on less fertile hillsides where rice could not be cultivated. Although sugar cane was a native crop of Taiwan, the indigenous people had never been able to make sugar granules from the raw sugar. Chinese immigrants brought and introduce the technique to turn the raw sugar cane into sugar granules. Sugar became the most important export item as the main purpose of producing sugar was to export it to other countries. The sugar produced in Taiwan made far higher profit than the sugar produced in Java. About 300,000 catties of sugar, which was one third of the total production, were carried to Persia in 1645. In 1658, Taiwan produced 1,730,000 catties of sugar and 800,000 catties of them were shipped to Persia and 600,000 catties to Japan. The rest was exported to Batavia. Tea was also a major export item. Another one of Taiwan's major export items was sulfur collected from near Keelung and Tamsui. Taiwan, especially Taoyuan, became an important transshipment center for East Asian trade networks. The products from Japan, Fukienn, Vietnam, Thailand, and Indonesia were shipped to Taiwan, and then exported to other countries as the markets demanded. The Dutch exported amber, spices, pepper, lead, tin, hemp, cotton, opium and kapok from Southeast Asia through Batavia to China by way of Taiwan and carried silk, porcelain, gold, and herbs from China to Japan and Europe via Taiwan. Agriculture The Dutch also employed Chinese to farm sugarcane and rice for export; some of this rice and sugar was exported as far as the markets of Persia. Attempts to persuade aboriginal tribesmen to give up hunting and adopt a sedentary farming lifestyle were unsuccessful because "for them, farming had two major drawbacks: first, according to the traditional sexual division of labor, it was women's work; second, it was labor-intensive drudgery." The Dutch therefore imported labour from China, and the era was the first to see mass Chinese immigration to the island, with one commentator estimating that 50–60,000 Chinese settled in Taiwan during the 38 years of Dutch rule. These settlers were encouraged with free transportation to the island, often on Dutch ships, and tools, oxen and seed to start farming. In return, the Dutch took a tenth of agricultural production as a tax. Taxation After the Dutch took control over Taiwan, they immediately levied a tax on all the import and export duties.