Dear Student,
Most of the fertile land went to Pakistan at the time of partition was the major reason food shortage in India after partition.
The following are some more reasons of food shortage in India after partition:
Low level of economic development
Demographic trends like high growth rate of population
Structural inequalities like caste system
Lack of opportunities in the form of education and employment to get out of poverty trap
Unequal distribution of resources in world economy
Regards