You trying to disown the child weather or not you want, is immoral in the eyes of the court - the child was born not because of his fault - you were one of the parties of the cause of his/her birth so morally speaking you cannot forget/disown him just because you and your wife did not jell well - if you do its a sin!!
Now to be able to answer your ? I need a few answers - Is the child a son or a daughter? Whats your qualification and job profile in what kind of Indian city? In what kind of Indian city is the wife and child currently? Are you heir to any ancestoral property? Whatz your wife's qualification/is she working, what profile? Do you want access to your child? What are your and your family's plans for the child?
Do not leave the scope for any kind of increase in terms of %age - for whatever happens your wife and her folks can come back a year later/periodically seek legal assistance in increasing it due to change of circumstances which could include inflation, you getting a better pay/job, she loosing her job, etc...etc....man explain your situation in brief...