<P> Slash - and - burn is used by 200 -- 500 million people worldwide . In 2004 it was estimated that in Brazil alone , 500,000 small farmers each cleared an average of one hectare ( 2.47105 acres ) of forest per year . The technique is not scalable or sustainable for large human populations . Methods such as Inga alley farming have been proposed as alternatives which would cause less environmental degradation . </P>
what is the main disadvantage of the slash and burn method of growing crops
not scalable or sustainable for large human populations