Distillery anaerobic digestion residues: A new opportunity for sweet potato fertilization

- The highest significant marketable yield was showed by T75 and T100.
- ADRs fertilization determined the highest nitrates content in aerial biomass.
- T75 treatment showed the highest nitrogen use efficiency.
- The ADRs fertilization increased glucose and fructose content in storage roots.

This paper represents an union point between two emerging issues: the productive potential derived from anaerobic digestion residues (ADRs) and the cultivation of sweet potato, an innovative species in Europe. The trial was carried out in open field condition in 2014 and 2015 comparing three fertilization treatments. ADRs were used to partially or completely substitute mineral N crop requirements: i) 50% N through ADRs and 50% N through mineral fertilizer (T50); ii) 75% N through ADRs and 25% N through mineral fertilizer (T75); iii) 100% N through ADRs (T100). Two controls treatments were also predisposed, one unfertilized (T0), and one with only mineral fertilization (TMIN).The highest significant aerial biomass yield (>57 t ha−1) was showed by T75 whereas no differences were found among other treatments (46 t ha−1). The highest significant marketable yield was showed by T75 and T100 (16 t ha−1). The marketable yield showed the highest value in 2015 with almost 16 t ha−1 with an year effect on root size. During the experiment harvest index ranged from 20.5% (TMIN) to 26.9% (T100).The nitrogen agronomic efficiency was greatly lower (−59.1%) in 2014 as a result of the high rainfall amount compared to 2015. T75 treatment showed the highest nitrogen agronomic efficiency, apparent recovery efficiency and utilization efficiency. The highest content of nitrates in aerial biomass was detected in combination with the N organic treatments.The storage roots harvested in 2014 presented a higher concentration of glucose (+19.7%) and fructose (+29.4%) than that harvested in 2015. The concentration of glucose and fructose increased with the amount of nitrogen supplied with ADRs. The obtained results offer potentially useful data for producers order to demonstrate the usability of ADRs as an alternative to traditional mineral fertilization in sweet potato cultivation.