Biomass yield and nitrogen use of potential C₄ and C₃ dedicated energy crops in a Mediterranean climate.

摘要

Biomass-based fuels from bioenergy crops stand as viable alternatives to fossil fuels. Side-by-side information on yields and N requirements of potential bioenergy crops is, however, lacking. The objectives of our study were to evaluate yields, N removal, and response to N fertilization of perennial C₄ and C₃ species under different N availability conditions in an irrigated Mediterranean climate. Five C₄ species - miscanthus (Miscanthus x giganteus Greef et Deu ex. Hodkinson et Renvoize), switchgrass (Panicum virgatum L.), big bluestem (Andropogon gerardii Vitman), bermudagrass (Cynodon dactylon L.), and elephantgrass (Cenchrus purpureus (Schumach.) Morrone)-, and two C₃ species - tall wheatgrass (Thinopyrum ponticum Podp.) and tall fescue (Festuca arundinacea Schreb.) - were evaluated under three N fertilization rates (0, 100, and 200 kg N ha-1 yr-1) from 2009 to 2011 in Davis, CA, USA. Miscanthus, switchgrass, big bluestem, and tall wheatgrass were harvested once per year, tall fescue twice, and bermudagrass four times per year. Elephantgrass was eventually excluded from our study due to winter mortality. The highest N-fertilized and unfertilized dry matter yields were achieved by miscanthus and switchgrass, followed by tall wheatgrass, big bluestem, tall fescue, and bermudagrass, with highest dry matter yields of 33.9, 22.9, 17.2, 16.2, 15.6, and 12.0 Mg ha-1 yr-1, respectively. Significant responses to N were observed for all crops in all years. Our results suggest that miscanthus and switchgrass have greatest potential as bioenergy crops for several reasons: (1) these crops had the highest yields and required only a single-harvest per year, (2) greatest response to N with yields increasing by 10.9 and 8.4 Mg ha-1 in the highest N treatment and fertilizer use efficiency of 69 and 55 kg biomass kg-1 N applied, respectively, and (3) lowest biomass N mass fraction of 3.6 and 2.6 g kg-1, respectively.