Rahul,
It appears that the company is an authorized automobile dealer. Accordingly, service tax shall not be leviable on selling of tractors since the same construes to be trading of goods. Transfer of title in goods is excluded from the definition of service. Trading in goods involves a transfer of title in goods, hence exempted. Moreover, trading of goods is included in the Negative list, therefore trading tractors as a dealer shall not be taxable.
However, the activity of servicing sold tractors shall be taxable. As per negative list based service tax regime, every service is taxable if its not covered by negative list or aby exemption notification. Since servicing of vehicles is nowhere exempted, therefore, it is taxable under service tax.
Accordingly the company needs to obtain service tax registration
For more details, the following link may be helpful:
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