For most of the period of Portuguese involvement, the people of Portuguese Guinea were subsistence farmers. In the 19th century, the coastal Balanta people, who were outside Portuguese control, had developed a sophisticated agricultural system, growing paddy-rice in reclaimed coastal swamps. Much of this rice was exported to surrounding territories, particularly after indigenous rice types were replaced by imported varieties. The Balanta also participated in the slave trade in this period. Another crop developed in this period was peanuts, and exports from Portuguese Guinea began in the mid 19th century. As intensive plantation cultivation led to reduced soil fertility, peanuts were normally grown by peasants in the Portuguese-controlled areas who mixed them with food crops and maintained fallow periods.