Question

Why little plants are kept in bag in nurseries and then transplanted to fields why?

Answer 1

Transplantation is the method of growing plants in which indirect seeding is done. In this method, first seeds are grown into seedlings inside a controlled environment of nurseries and then seedlings are transplanted to a field. 

This method has many advantages  such as:

The seeds are not exposed to birds, rats,  snails and other biotic  and abiotic stress, which has a chance in direct seeding.
 
 In this method, there is lesser ​crop-weed competition, as main plant  and weeds are not of similar age.

In this method, even the foreign plants get time to acclimatise and so then can grow well in the new place.