Long-term studies on switchgrass grown on a marginal area in Greece under different varieties and nitrogen fertilization rates

Switchgrass (Panicum virgatum L.) is a perennial grass that has been selected as a candidate bioenergy crop for USA in the early 80s, while the research in Europe started a decade later. A long-term study on switchgrass had been carried out (1998-2015) on a marginal area in Greece comparing five varieties (having lowland or upland ecotype) at increasing nitrogen fertilization rates (0, 75 and 150 kg N ha−1). Due to the successful establishment of the plantation quite satisfactory yields were recorded even at the establishment year (8.9 Mg DM ha−1) and the ceiling yields were recorded in the 2nd year and came up to 20 Mg DM ha−1. The under study lowland varieties (Alamo, Kanlow and Pangburn) were more productive compared to the upland varieties (Blackwell and CIR) with mean dry yields 12.37 and 11.39 Mg ha−1, respectively and showed higher resistance to lodging. Among the five under study varieties, Alamo was the best performing giving an average yield of 12.7 Mg DM ha−1, averaged over all treatments and years, while CIR was the least performing producing a corresponding average yield of 10.8 Mg DM ha−1. From the fourth growing season and onwards significantly higher yields were recorded under increasing N fertilization up to 150 kg N ha−1 with an average yield of 13.9 Mg DM ha−1 (150 kg N/ha) over all varieties and years. The corresponding yields for the other two tested nitrogen rates (0 and 75 kg N/ha) were 10.31 and 11.69 Mg DM ha−1, respectively.