Biomass yield and nitrogen use efficiency of cellulosic energy crops for ethanol production

With the global increase in energy production from cellulosic crops, high biomass production of energy crops based on lower inputs, particularly less fertilizer and mechanization, are expected. To determine candidate energy crops adapted to temperate Japan and establish a corresponding low-nitrogen-input cultivation system, we preliminarily examined the biomass yield performance and nitrogen consumption of five important cellulosic energy crops, Erianthus, johnsongrass, switchgrass, sorghum, and napiergrass, in comparison with maize and sugarcane (first-generation energy crops) under conventional and higher planting densities. Napiergrass had the highest dry biomass yield with 53.2 t ha−1 y−1 on average, followed in order by sorghum, maize, sugarcane, switchgrass, johnsongrass, and Erianthus. Nitrogen absorption was closely correlated with biomass yield (r = 0.96, significant at the 1% level). Nitrogen absorption by napiergrass (up to 775.1 kg ha−1) was 10-fold higher than nitrogen application by chemical fertilizer (72 kg ha−1). There was a significant difference in nitrogen use efficiency between planting densities. We suggest a higher-density design within the suitable density range to improve nitrogen use efficiency and decrease nitrogen depletion from the soil.

► Napiergrass achieved the highest biomass yield in temperate Japan as a energy crop.
► Nitrogen absorption was closely correlated with biomass yield.
► Nitrogen absorption by napiergrass was 10-fold higher than nitrogen application.
► Nitrogen use efficiency was significantly higher at higher planting density.