Evaluation of Nitrogen and Phosphorus Release from Enriched Biochar and Mixture of Biochar and Layered Double Hydroxides

Meeting the increasing global food demand has required an intensification of agricultural production, largely supported by the extensive use of chemical fertilizers. While effective in raising yields, their overuse has resulted in significant environmental challenges. Therefore, developing fertilizers that are both efficient and sustainable is a key priority. Biochar-based enhanced efficiency fertilizers (EEFs) represent a promising alternative, as they can regulate nutrient release in line with plant requirements, thereby minimizing nutrient losses, mainly through leaching and evaporation. In this work, vineyard pruning biochar (BV) was investigated as a matrix for producing EEFs. Two nutrient incorporation strategies were compared: direct enrichment with nitrogen (BV-N) and phosphorus (BV-P) and combinations of BV with nutrient-loaded layered double hydroxides (LDH-N and LDH-P). Nutrient release was first evaluated in static water systems and subsequently in soil-mimicking column leaching experiments. Results showed that unmodified BV released only small nutrient amounts (0.24 mg of N and 0.49 mg of P), whereas enriched biochars provided substantially higher nutrient release after 72 hours (11.32 mg N/g and 4.85 mg P/g). Among the tested formulations, BV-N achieved a more gradual nitrogen release profile, while LDH-P allowed for a more extended phosphorus supply. Overall, these results emphasize the potential of biochar-based fertilizers not only to improve nutrient use efficiency but also to support circular economy practices by valorizing agricultural residues.