Switchgrass and Alfalfa as Cellulosic Biofuels: Possibilities and Limits

Perennial crops which produce high cellulose yields have the potential as non-fossil fuel energy sources for the future, due to a number of environmental benefits, and potentially higher energy yields compared with grains. However, considerable technical barriers for cellulosic conversion to fuel remain. From an agronomic perspective, alfalfa and switchgrass have important positive features as cellulosic feedstocks. They are both perennials which have environmental advantages and are high yielding in California. Alfalfa has the advantage of zero N fertilizer requirement, wide adaptation, known production systems, and significant environmental benefits. In the past 2 years, we have experimented with switchgrass under irrigation at 4 locations in California, and yields of 10-15 tons/acre appear to be feasible in the first year of production. A ‘high productivity’ multiple-use scenario for irrigated biofuels appears more appropriate than ‘low input’ strategies. This could be accomplished through different cuts for different purposes, or leaf-stem fractionation. This concept has the advantage of producing multiple-value streams, avoiding the food-food conflict, stabilizing supply, and increasing options for growers. The high demand for all forage crops (even straws) for other purposes will present an economic challenge for biofuel feedstocks. Potential cellulosic crops should be evaluated carefully from a range of perspectives, including water and N use, environmental impacts, and whole-system viability, to develop sustainable systems for the future.