The agronomic efficiency of applied N varied from 5 to 14 kg DM yield per kg N applied.
The physiological efficiency varied from 79 to 123 kg DM yield per kg N uptake.
The average indigenous soil N supply was about 100 kg N ha−1 per harvest cycle.
The yield performance of the unfertilized poplar is encouraging.
The rise of N content is detrimental for the quality of the feedstock product.