Question

Explain in
Why it is not as rich a food granary as the ganga brahmaputra basin in India

Answer 1

because in amazon bank lot of forest are there
so less use of water for production of food..

Answer 2

The delta of the Ganga Brahmaputra basin in India is extremely fertile because every year the soils of this area gets flooded and gathers minerals from river basin.  

The delta of the Ganga Brahmaputra basin is one of the biggest deltas of the world and the agricultural lands of this basis gets complete river advantage. That is why it is a rich food granary.