Adoption of Miscanthus as a bioenergy crop on US croplands: impacts on soil carbon and water

This study evaluated the potential impact of cultivating Miscanthus (Miscanthus x giganteus) as a bioenergy crop on the soil organic carbon (SOC) pool of the croplands of US. Similarly, the crop areas where Miscanthus can be grown up to potential yield without supplemental irrigation were identified. The productivity of Miscanthus was modeled using the biophysical model MiscanMod and spatial analysis. The productivity for harvestable biomass ranged from 11.7 to 26 Mg ha-1 yr-1, with a spatial average of 19 Mg ha-1 yr-1and a coefficient of variation of 13%. This variation resulted primarily from spatial heterogeneity of growing degree days and solar radiation interception. The model assumes adequate nutrients and moisture availability for Miscanthus growth, therefore showing a maximum possible productivity. Our result suggests that approximately 485 kg C ha-1 yr-1 would enter the SOC pool from the above ground biomass such as senesced leaves and post harvest remnants on the soil surface. Similarly, the total C input from both canopy and root system will range from 2.5 - 5 Mg C ha-1 yr-1. This would result in a net SOC sequestration rate of 0.36 - 0.72 Mg C ha-1 yr-1 across the croplands of the US. Productivity predictions, along with the effective rainfall estimates, were then used to project areas in which Miscanthus can be cultivated to its potential yield as a rainfed crop as well as those where it would require additional irrigation in order to meet the crop water demand. To meet the targets of the US Energy and Independence and Security Act of 2007 (36 billion gallons of biofuel ethanol per year by 2022) using Miscanthus as feedstock, 19 million ha of cropland would be needed which is 16% less than the current cropland under corn-based ethanol production.