Comparing repeated forage bermudagrass harvest data to single, accumulated bioenergy feedstock harvests

Bermudagrass (Cynodon dactylon L.), widely grown for forage in the southeastern USA and throughout tropical and sub-tropical environments, is now being considered as a potential cellulosic bioenergy feedstock. The question is whether we can utilize extant forage data that seeks to balance yield with nutritive value to estimate its yield under single, yearly harvests designed purely for maximizing cellulosic biomass yield? To contribute to our knowledge of yield potentials and mineral concentrations in biomass-harvest regimens where nutritive value to ruminants is not a factor, ‘Tifton 85’ and ‘Coastal’ accumulated bermudagrass was harvested at 14-day intervals and compared to 21-day repeated harvests. Coastal accumulated biomass earlier but ended growing seasons with dry matter (DM) and carbon (C) yields comparable to Tifton 85. Peak yields were approximately 6.1 Mg ha−1 yr−1 during a growing season with 459 mm rainfall but ranged from 10.3 to 11.2 Mg ha−1 yr−1 during a growing season with 845 mm rain. Average peak accumulated harvests out-yielded cumulative 21-day repeated harvest DM by 44% and C by 47% over two years; 21-day harvest material yielded 84% more N than the accumulated material. Results indicate that bermudagrass yields and mineral concentrations reported for forage trials are not directly applicable to biomass-harvest regimens. If similar data is collected from a number of other locations to confirm our findings, we may be able to formulate predictions or mathematical models of bermudagrass biomass production based on already available forage yield data.