Tobacco farmers know there's not a cash crop they can grow that's as lucrative.

CNN: The Tobacco Deal: Smoke And Mirrors?

Besides being a cash crop, it is used as medicine and, as part of tribal culture, smoked on special occasions.

ECONOMIST: An opium ban is a mixed blessing

Over the next two centuries, the growth of tobacco as a cash crop fueled the demand in North America for slave labor.

CNN: A brief history of tobacco

For some 60, 000 families in Peru who survive on growing coca it is a valuable cash crop.

BBC: Peru is the biggest producer of cocaine after Colombia

Many Afghan farmers are reluctant to switch to a new cash crop because they are accustomed to being paid upfront to grow poppies for opium traders.

NPR: Promoting Perfume, Not Poppies, in Afghanistan

But in a country where over 40% of the population are hill-tribesmen, many of them dependent on opium as a cash-crop and for medicine, it is proving tricky.

ECONOMIST: Calls to re-legalise opium

The islands' traditional cash crop, cloves, faces a bleak future.

ECONOMIST: Zanzibar