Jhoom or Jhum Farming is the most ancient form of farming practiced by mainly the tribal peoples of northeastern states of India like Arunachal Pradesh, Meghalaya, Mizoram and Nagaland and some districts of Bangladesh also. Jhum/Jhoom farming or cultivation method is usually practiced in the hilly areas having thickly forest area.
In Jhoom farming a portion of forest is cut down and all the trees and weeds or grasses are burnt and left for some time say 6 monthes, or a year. It is believed that this burnt ash of trees and weeds makes the soil fertile. After the soil is fertile enough seeds and crops are planted. Crops which do not require large amount of water are usually cultivated.
But in this type of farming, after few cycles (getting crop for 2 to 4 seasons) soil looses its fertility and the people move to some other place for farming. In this type of farming due to cutting down of trees soil erosion is a major problem also you have to destroy the whole forest and you can use the land only till the soil is fertile, after that land is of no use. Due to these reasons in some areas like Meghalaya, Mizoram, Jhum farming has been stopped.
All of you are right.I would like to add one main & most important thing of Jhoom farming is that how the land is framed.
Actually in hilly terrain , water can not be reversed in the slopes, So farmers cut the land as steps, each steps are almost made plain to reserve the needed amount of water for farming.
Photos attached for yor reference.