Effect of the anaerobic digestion residues use on lettuce yield and quality

• The use of ADRs appears to be efficient if integrated with mineral fertilization.
• The benefits of using ADRs are related to the addition of organic matter in the soil.
• The ADRs produce no negative effects on lettuce quality and yield.
• The nitrates content in lettuce was below the EU limits.
• The partial replacement of fertilizers with ADRs represents an environmental advantage.

In the last years, fertilization has become an agricultural practice with several different aspects. This paper suggests the use of a distillery residue as an organic nitrogen fertilizer. It derives from the process of anaerobic digestion of fruits and dregs (ADRs), both used to produce biogas.The field experiment was conducted on two spring-summer varieties of lettuce (butterhead and open batavia). Five fertilization treatments were tested supplying nitrogen in mineral form and with different ADRs rates. Dry matter content, antioxidant capacity, concentrations of total phenols, ascorbic acid, phenolic acids, organic nitrogen, nitrates and heavy metal, and some nitrogen use indexes were evaluated.The use of ADRs as organic nitrogen fertilizer produces no negative effect on plant growth, maintaining the qualitative aspects unchanged. Nitrate contents were below the most stringent limits imposed by the EU regulation in all treatments and ADRs showed no contraindications to their use for organic fertilization of this vegetable. The benefits of using this product are related to the addition of organic matter in the soil, reducing fertilizer and environmental costs.