Vermicomposting amended with microalgal biomass and biochar produce phytopathogen-resistant seedbeds for vegetables

Vermicomposting is used to treat and recycle organic waste to be utilized in agriculture. This project aimed to improve the product of vermicomposting by adding biochar and microalgal biomass to the process. Experiment to vermicompost (60 days) mixed organic waste was carried out preparing 16 different treatments. The best treatment appeared to be the earthworm Eisenia fetida, 6% biochar, and the biomass of the microalgae Navicula sp. amended to the process. The product was mature vermicompost with pH 7, cation exchange capacity 70 cmolc kg⁻¹, and the C:N ratio 9.5. All products were used as seedbeds and tested for the plant growth promotion of the vegetables Solanum lycopersicum, Capsicum annuum, and Solanum melongena. The best vermicomposting product increased plant growth, reduced the disease incidence of the leaves, and improved the disease resistance of the seeds the plants produced. Plant vigor index was highest in the best treatment varying between 4600 and 5000 depending on the plant species. For comparison, the lowest values were under 1000. Disease resistance was low for the best treatment (5%–15%) compared to the high values over 60%. The seeds ripened in the experimental plants had acquired resistance against the experimentally inoculated phytopathogen Pythium sp., known to commonly destroy seeds. In the best treatment, more than 90% of the seeds germinated while in all other treatments less than 56% germinated. In conclusion, the vermicomposting using the earthworm Eisenia fetida, 6% biochar, and the biomass of the microalgae Navicula sp. produced seedbed substate that improved the growth of vegetables and suppressed phytopathogens. The seedbed can be used in sustainable agriculture to reduce the use of fertilizers and chemicals.