Enhancing the fertilizing properties of digestate’s solid fraction by Trichoderma-driven microbial activation: In-field application effects on tomato growth

Bio-based fertilizers (BBFs) derived from animal manure hold great potential to optimize resource recovery and boost agricultural yields. Digestate use in agriculture is common and its solid fraction is often recommended as an organic amendment. The fertilization potential of digestate solid fraction can be further improved by using beneficial customized microbial consortia. The upgrading of digestates solid fraction with ad hoc microbial consortia is a novel option paving the way towards a synergy between circular economy and upgraded organic agriculture. This field study evaluated the fertilization efficiency of a digestate solid fraction derived from energy crops and bovine manure, either alone (DF) or activated with a microbial consortium (ADF), in comparison with chemical fertilization (CF) and an unfertilized control (NF), using a randomized experimental design with three replicated field plots per treatment. Results demonstrated that microbial activation improved the fertilization performance of the BBF leading to tomato yields (78 ± 11 t ha − 1 ) similar to chemical fertilization (61 ± 15 t ha − 1 ), while improving plant health and extending the productive period. Metagenomic analyses showed that the fungal inoculants ( Trichoderma spp. and Metarhizium anisopliae ) persisted in the rhizosphere, whereas the bacterial inoculants ( Azospirillum brasilense and Lactiplantibacillus plantarum ) were not detected in soil samples after application, suggesting that the beneficial effects were mainly associated with the fungal component of the consortium. These results were further compared across multiple scales, from greenhouse to full-field, to ensure agronomic robustness and comparable yields to chemical fertilization across increasing environmental complexity. At field scale, biological activation has the potential to match chemical fertilizers yield and improve nutritional parameters, therefore paving the way to develop new BBFs formulations with custom microbial consortia to address specific plant, soil, and environmental requirements looking towards meeting Sustainable Development Goals. Further studies are needed to improve the mechanistic understanding of the synergy between BBFs, microbial drivers and soil.