<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Slash - and - burn agriculture, or fire--fallow cultivation, is a farming method that involves the cutting and burning of plants in a forest or woodland to create a field called a swidden . (Preparing fields by deforestation is called assarting .) In subsistence agriculture, slash - and - burn typically uses little technology . It is often applied in shifting cultivation agriculture (such as in the Amazon rainforest) and in transhumance livestock herding . </P> <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> <P> Historically, slash - and - burn cultivation has been practiced throughout much of the world, in grasslands as well as woodlands . </P>

What is the main disadvantage of the slash and burn method of growing crops