Effect of irrigation and nitrogen fertilization on biomass yield and efficiency of energy use of Miscanthus

The perennial C4 grass Miscanthus has been proposed as a biomass energy crop in Europe. Effects of crop age, irrigation and nitrogen fertilization on biomass and energy yields and N content of Miscanthus were investigated and the energy costs of production determined. After an establishment period of 1 year, cultivation of Miscanthus resulted in a dry matter production of over 37 t ha-1 year-1 over a period of 4 years. Irrigation and nitrogen level greatly affected Miscanthus biomass yield. In absence of N fertilization, irrigation did not modify biomass yield and the effect of irrigation increased with the increase in N level. The average N response ranged from 37 to 50 kg biomass kg-1 N applied. Because the calorific value of Miscanthus biomass (16.5 MJ kg-1) was not affected by irrigation and N fertilization, energy production depended exclusively on biomass yield. Maximum energy yield was 564 GJ ha-1 year-1. Without N supply and irrigation, energy yield was 291 GJ ha-1. Net energy yield, calculated as the difference between energy output and input, but without inclusion of drying costs, was 543 GJ ha-1 with N fertilization and irrigation and 284 GJ ha-1 without; the ratios of energy output to input in crop production were 22 and 47, respectively.