Miscanthus Yields and Tissue N Concentrations during Establishment with Various N-Rates Grown on Marginal Soils.

Our understanding of nitrogen (N) fertilization during establishment of Miscanthus x giganteus remains fragmented and incomplete. It is not clear how N fertilization may influence the composition of the harvested biomass feedstocks or development and growth of belowground roots and rhizomes. Our goals were to identify: 1) optimal N fertilization strategies during Miscanthus establishment; and 2) how N fertility affects plant growth and development, and biomass composition. Four Miscanthus genotypes (Illinois clone, Mississippi clone, Nagara, and Nagara-sib) were planted near Schochoh, KY and Lafayette, IN in 2010. The fertilization rates were split over years with both years receiving the N rates (0, 50, 75, 100, 150 kg N ha^-1) with the second year rates bringing the two year total to 150 kg N ha^-1 except for 0-0 and 150-150 kg N ha^-1 treatments. Tissue N concentrations of both above and belowground organs reflected the rate of N fertilization in both years across both locations.  Yield response trends were similar across genotypes, but varied by location and year with the highest biomass yields typically obtained at the 75 kg N ha^-1. Concentrations of carbon, hemicellulose, cellulose, lignin, and ash were rarely influenced by N-fertilization, but differed among genotypes. This difference among the genotypes is attributed to lower leaf-to-stem ratio of the IL and MS clones compared to Nagara and Nagara-sib genotypes. High N rates also altered partitioning resulting in increased belowground biomass and greater rhizome protein and amino acid concentrations. Based on these data Miscanthus should receive a steady supply of N at approximately 50-100 kg ha^-1.