Many biogas plants take a wide range of substrates. As well as beet and traditional grass mixtures, you can use grass from wetlands and nature reserves. By overseeding wetland with suitable grasses such as timothy, meadow fescue, festulolium festuca type and festulolium lolium type, you can improve your biomass yield.
In organic farming, your substrate grass mixture could also double up as a source of fertiliser. Grass mixtures with a reasonable amount of red clover, for example, will improve the nitrogen. And after digestion, you can spread the substrate back on the land.