How can slash and burn agriculture become environment friendly? 

Explanation

Slash and burn agriculture, commonly called as Jhum cultivation in the north-eastern states of India.
  It has also contributed to deforestation.
In slash and bum agriculture, the farmers cut down the trees of the forest and burn the plant remains.
The ash is used as a fertilizer and the land is then used for farming or cattle grazing.
After cultivation, the area is left for several years so as to allow its recovery.
The farmers then move on to other areas and repeat this process.
In earlier days, when Jhum cultivation was in prevalence, enough time-gap was given such that the land recovered from the effect of cultivation.
With increasing population and repeated cultivation, this recovery phase is done away with, resulting in deforestation.