Village Sarpanch has no power to block the road because that land has been used as a road for very long time. The general public have accrued an easement in respect of that land. There is no approach road to access your land. In this situation you have the right to access you land through that government land.
You should move an application to the Tehsildar against the illegal act of Sarpanch. Though, it is a government land and Sarpanch has the right to protect each an every government property vested or situated in his village. But, he can exercise this power against the encroachment on the government land. There is no encroachment but it has been used by public from so many years.
Tehsildar will direct the Sarpanch to unblock the road because you have no other way or road to access your field. The Government issues a notice to the person encroaching a government land and that notice is issued by the Tehsildar. Tehsildar issues that notice either upon a report of Lekhpal or a complaint from villagers including Sarpanch. There is no notice issued against you. So, you should approach the concerned Tehsildar for issue a proper order in your case.
File a complaint against the act of Sarpanch
You should immediately make a complaint before the Collector against such an illegal act of Sarpanch. Collector is the custodian of government land. He has the power to restrict arbitrary action of a person in respect of government land. This is an arbitrary action which is illegal in the eyes of law. You have accrued a right of easement in that land because you have been using that land for long time.