Effects of digestate-encapsulated biochar on plant growth, soil microbiome and nitrogen leaching

The increasing amount of food waste and the excessive use of mineral fertilizers have caused detrimental impacts on soil, water, and air quality. Though digestate derived from food waste has been reported to partially replace fertilizer, its efficiency requires further improvement. In this study, the effects of digestate-encapsulated biochar were comprehensively investigated based on growth of an ornamental plant, soil characteristics, nutrient leaching and soil microbiome. Results showed that except for biochar, the tested fertilizers and soil additives, i.e., digestate, compost, commercial fertilizer, digestate-encapsulated biochar had positive effects on plants. Espe-cially, the digestate-encapsulated biochar had the best effectiveness as evidenced by 9-25% increase in chlo-rophyll content index, fresh weight, leaf area and blossom frequency. For the effects of fertilizers or soil additives on soil characteristics and nutrient retention, the digestate-encapsulated biochar leached least N-nutrients (<8%), while the compost, digestate and mineral fertilizer leached up to 25% N-nutrients. All the treatments had minimal effects on the soil properties of pH and electrical conductivity. According to the microbial analysis, the digestate-encapsulated biochar has the comparable role with compost in improving the soil immune system against pathogen infection. The metagenomics coupling with qPCR analysis suggested that digestate-encapsulated biochar boosted the nitrification process and inhibited the denitrification process. This study provides an extensive understanding into the impacts of the digestate-encapsulated biochar on an ornamental plant and offers practical implications for the choice of sustainable fertilizers or soil additives and food-waste digestate management.

Automated summary

The increasing food waste and excessive use of mineral fertilizers have had harmful effects on soil, water, and air quality. To address this issue, the study investigated the effects of digestate-encapsulated biochar on plant growth, soil characteristics, nutrient leaching, and soil microbiome. The results showed that digestate-encapsulated biochar had positive effects on plants and was the most effective in increasing chlorophyll content, fresh weight, leaf area, and blossom frequency. In terms of soil characteristics and nutrient retention, digestate-encapsulated biochar had the least nutrient leaching compared to other fertilizers and soil additives. Additionally, it improved the soil immune system and promoted the nitrification process while inhibiting denitrification. This study provides valuable insights into the use of digestate-encapsulated biochar as a sustainable fertilizer or soil additive, as well as the management of food waste digestate.