The wages that coffee pickers receive may be their only source of annual income. Workers typically have little education and few employment options. Because coffee growers have many costs, often carry debts, and receive low prices, they find it difficult to increase wages and still make a profit. The average coffee plantation requires about 250–300 workdays ("man-days") of labor per hectare (2.5 acres). Robusta coffee can be harvested by machine; this works in parts of Brazil where extensive plantations grow on flat land. But mechanical harvesting takes all cherries at once—ripe, unripe, and spoiled—along with twigs, leaves, and broken branches. Throughout the modern history of coffee, the ways that individual growers, and regional and national governments, addressed the labor "problem" has varied greatly. Farmers' options and constraints relate to the size of their plantations as well as the larger socioeconomic and political system in which they live.