Vast tracts of land which are suitable for growing grazing grasses or trees, but little else, have been torn up to make way for cotton, peanut or coffee plantations. The result is soil that becomes poor in humus and loses its cohesiveness.
In Brazil many of the abandoned coffee lands are so ruined that they cannot be restored to crop production or the humus content of the soil is seriously reduced. Coffee plantations are always on the march, grabbing new land and leaving behind eroded soils. Many of the lands of the Taureg people, who have led a nomadic life for centuries on the edge of the Sahara, have been taken over to grow export crops like peanuts for European markets. Bad farming techniques are turning the marginal land into desert.