2 Answers
As a first step, please talk to nearest NABARD Bank and check about the assistance they provide for starting soil testing lab, refer to LInk for More Information https://www.nabard.org/english/soil_testing.aspx
2) You might also need to talk to District Agriculture/Soil Conservation Officer and enquire with them the actual approval needed and process.
Also, please refer to http://agricoop.nic.in/dacdivision/mmsoil280311.pdf