GST Registration is required in milk trading turnover above 50 crore

As per Notification .1/2017 CT it's Exempted & as long as you are deals in supply Expempted goods you are not liable to obtain Registration.

If there is no taxable turnover, you are not required to take registration. however, if total turnover (taxable + exempt) exceed limit of Rs
20 lacs/ 40 lacs, you are required to take registration. it means, if in your case there is a very small taxable supply, you shall be required to take registration.