The Sustainability of Switchgrass Cropping Systems.

Switchgrass (Panicum virgatum L.) is a perennial C4 grass that is native to the eastern two thirds of temperate North America.  It has been used for conservation purposes and as a pasture grass since the 1940’s. It is currently being developed as a cellulosic biomass energy crop because it can produce high biomass yields on marginal croplands where it effectively controls soil erosion. There are several sustainability issues that must be addressed with any energy crop.  These include economic, production system, net energy, and carbon and greenhouse gas sustainability.  Recent studies have demonstrated that switchgrass biomass production costs of $50 Mg^-1 are feasible and at a conversion rate of 0.38 L kg-1, farmgate feedstock costs would be ~$0.13 L^-1 ($0.49 gallon^-1).  On farm trials also have demonstrated that switchgrass can produce 13X more energy as ethanol and 540% more renewable than non-renewable energy required for its production.  In a five year period, switchgrass fields managed for biomass production had average increases in soil organic carbon (SOC) of 2.9 Mg C ha^-1 yr^-1 because of its extensive and deep root system.  Because of its low input requirements and substantial SOC sequestration, switchgrass production systems are greenhouse gas neutral or negative. Other research has shown that switchgrass plots managed for biomass energy can maintain high yields indefinitely.  In summary, switchgrass cropping systems for biomass energy can be very sustainable with good management.