Biomass Yield Stability of Switchgrass Cultivars

INTRODUCTION The development of viable bio-based energy systems offers many potential benefits relative to energy availability, national security, a cleaner environment, and associated economic rewards (DOE 2000). Largescale bioenergy use will require the deployment of environmentally acceptable energy crops and cropping systems for producing large quantities of low-cost, high-quality biomass feedstocks (DOE 1999). Switchgrass (Panicum virgatum L., Poaceae), an indigenous perennial herbaceous species distributed over much of the contiguous US, was chosen by the Department of Energy (DOE) as the model herbaceous species for development as a bioenergy feedstock crop. It was chosen on the basis of its wide adaptation, high production potential on marginal soils, and tolerance to biotic and abiotic stress agents (McLaughlin 1993). Based on morphology and habitat preference, switchgrass has been classified into upland and lowland ecotypes (Porter 1966). Lowland ecotypes are adapted to flood plains and are generally taller, larger in tiller diameter, and more robust than their upland counterparts (Anon. 1954; Porter 1966). The much higher dry matter (DM) yield capability of the robust lowland cultivars compared to the smaller, less robust, upland ecotype cultivars in the southern US is well documented (Anon. 1954; Porter 1966; Sladden et al. 1991). What is less well documented is the capability of cultivars for sustained high DM production, particularly lowland cultivars grown on non-alluvial soils or marginal soils, or both. In addition, very little information is available on cultivar by environment (CE) interactions for such studies, which are of major importance in selecting and developing improved switchgrass cultivars. CE interaction causes difficulty in identifying those cultivars that perform best over the range of environmental conditions to which they will be exposed (Eberhart and Russell 1966). Therefore, this study was initiated to evaluate long-term yield performance of selected commercial upland and lowland switchgrass cultivars and cultivar blends and to estimate and characterize the magnitude of CE interaction.