Perennial herbaceous crops as a feedstock for energy and industrial purposes: Organic and mineral fertilizers versus biomass yield and efficient nitrogen utilization

Perennial herbaceous crops (PHC) could be a feedstock for energy and industrial purposes. Not much is known on the effect of fertilization of PHC with biogas plant digestate. The study analysed three forms of biogas plant digestate and mineral fertilizers on the yield PHC and nitrogen (N)-use efficiency in three consecutive harvest cycles. The PHC were: Helianthus tuberosus, Sida hermaphrodita, Helianthus salicifolius, and Miscanthus x giganteus. The forms of fertilization were: wet digestate, dry digestate, torrefied digestate, mineral fertilization and control (no fertilization). The level of N fertilization were: N 85 and 170 kg ha(-1). Fertilization of PHC, except Miscanthus x giganteus, and an increase in the nitrogen rate generally increased the yield compared with the control plots. The highest yield of 15 Mg ha(-1) DM was achieved for Helianthus salicifolius in the third year where mineral fertilization, dry digestate was applied and on the control plot. The yield of Miscanthus x giganteus and Sida hermaphrodita also increased in consecutive years, but it was much lower than Helianthus salicifolius. Helianthus tuberosus had an opposite yield relationship and gave the highest yield in the first year. The agronomic efficiency and recovery efficiency of applied N indices were the highest for HT and the lowest for MG. It could be stated that in the initial years of cultivation, from the perspective of yielding and nitrogen use efficiency, the fertilisation of PHC was partially justified, while it was not justified in Miscanthus x giganteus.