I have written an article explaining about GST on bloggers and web-publishers. You can read that article for complete understating.
However to answer your question, if you are earning only from Adsense then you are not required to take GST registration. As Adsense income falls under the definition of export supplies and again covered under definition of zero rated supplies.
chatCommentsThis answer summarise everything. For better understanding should read the article, it gives 360 degree view of applcability of GST on bloggers and website publishers including affilliate incomes. - GST PayerAdsense payments are made in $. Paying entity is, Google Asia Pacific Pte. Ltd. 70 Pasir Panjang Road, #03-71, Mapletree Business City, Singapore 117371 (pl. see payment details in the adsense a/c.) None of the conditions mentioned are satisfied in section 13(12) in order to be taxable. An early clarification on adsense payments by the GST authorities will help the online publishers from going through the ordeal of monthly statements and penalties for not registering. - mahmood faheem