Existing carbon trading programs active in the agricultural sector provide little incentive to hemp farmers, or any farmers, really.  There is very little liquidity in agricultural carbon banks in the US.  USDA Secretary Tom Vilsack estimates that out of ~134 million outstanding credits, only 2.5 million are in agriculture.  Most of the carbon trading worldwide occurs in the energy sector, and this is true for the US. 

Establishing a carbon trading scheme for agriculture is a long-term project.  Some stakeholders, like the Food and Agriculture Climate Alliance