According to Friedrich et al. (On-line available at the link below), about 9% of the global arable land (approximately 125 million hectares) are under no-till agriculture. These arable lands are considered as under varying degrees of conservation agriculture. This publication also has a Table presenting the extent of land where conservation agriculture being practiced in different countries. You may find it is very helpful.
-SJ
Friedrich, T., Derpsch, R. & Kassam, A. (2012) Overview of the global spread of conservation agriculture. Field Actions Sci. Rep. 6, 1941 (https://factsreports.revues.org/1941)