Twenty-Year Biomass Yields for Eight Switchgrass Varieties in Alabama.

Short-term research on switchgrass (Panicum virgatum) has shown that it has substantial potential as a cellulosic biomass crop. Long-term experiments are needed to determine stand longevity and yield response to factors such as rainfall, which have critical economic implications. However, no information has been published on long-term yields of different varieties of switchgrass. Consequently, data from a replicated small-plot experiment which included six switchgrass varieties that were planted during spring of 1988 in south central Alabama were analyzed, and are presented in this study. Varieties included two lowland types of switchgrass, ‘Alamo’ and ‘Kanlow’, and six upland types, ‘Cave-in-Rock’, ‘Blackwell’, ‘Summer’, ‘Trailblazer’, ‘Pathfinder’, and “Kansas Native’. Plots were fertilized at a moderate level, and were harvested twice a year in mid-summer and again in fall, from 1999 to 2009, providing a unique long-term dataset. Alamo provided the highest average yield (23.4 Mg ha^-1 yr^-1), followed by Kanlow (18.7 Mg ha^-1 yr^-1) and Cave-in-Rock (14.6 Mg ha^-1 yr^-1). In 2007 Alabama experienced the worst drought in over a hundred years. Most traditional row crops such as corn, cotton and soybeans did not provide sufficient yields to justify the cost of harvesting, but the drought had a relatively small effect on switchgrass yield. We conclude that; 1) Alamo is the most suitable variety of switchgrass for the Southeastern USA; 2) switchgrass is extremely tolerant of drought; and 3) stands of switchgrass can be expected to remain productive for over 20 years if they are properly managed for cellulosic biomass production.