The pyrolysis process of residues has emerged as a sustainable method for managing organic waste, producing biochars that offer significant benefits for agriculture and the environment. These benefits depend on the properties of the raw biomass and the pyrolysis conditions, such as washing and drying. This study investigated biochar production through slow pyrolysis at 300 °C, using eight biomass types, four being plant residues (PBR)—sugarcane bagasse, filter cake, sawdust, and stranded algae—and four non-plant-based residues (NPBR)—poultry litter, sheep manure, layer chicken manure, and sewage sludge. The physicochemical properties assessed included yield, carbon (C) and nitrogen (N) content, electrical conductivity, pH, macro- and micronutrients, and potentially toxic metals. Pyrolysis generally increased pH and concentrated C, N, phosphorus (P), and other nutrients while reducing electrical conductivity, C/N ratio, potassium (K), and sulfur (S) contents. The increases in the pH of the biochars in relation to the respective biomasses were between 0.3 and 1.9, with the greatest differences observed for the NPBR biochars. Biochars from sugarcane bagasse and sawdust exhibited high C content (74.57–77.67%), highlighting their potential use for C sequestration. Filter cake biochar excelled in P (14.28 g kg⁻¹) and micronutrients, while algae biochar showed elevated N, calcium (Ca), and boron (B) levels. NPBR biochars were rich in N (2.28–3.67%) and P (20.7–43.4 g kg⁻¹), making them ideal fertilizers. Although sewage sludge biochar contained higher levels of potentially toxic metals, these remained within regulatory limits. This research highlights variations in the composition of biochars depending on the characteristics of the original biomass and the pyrolysis process, to contribute to the production of customized biochars for the purposes of their application in the soil. Biochars derived from exclusively plant biomasses showed important aspects related to the recovery of carbon from biomass and can be preferred as biochar used to sequester carbon in the soil. On the other hand, biochars obtained from residues with some animal contributions are more enriched in nutrients and should be directed to the management of soil fertility.

The incorporation of organic amendments into the soil offers numerous long-term benefits. Waste from Tenebrio molitor larvae production, including feces, exoskeletons, and feed residue, can serve as a valuable organic fertilizer. However, factors such as the type of waste, application rate, decomposition stage, and soil characteristics can significantly impact plant growth. This study evaluates the effectiveness of yellow mealworm frass as a biofertilizer for tomato plants. The waste was incorporated into the soil at concentrations of 0, 1, 2, 3, 4, and 5 % (v/v) and incubated for 0, 10, and 20 days, after which ten tomato seeds were sown. Seedling emergence, as well as the fresh and dry weights of the tomato plants, were evaluated weekly. Additionally, the impact on tomato plant growth was studied under greenhouse conditions. The results indicated that yellow mealworm frass did not exhibit phytotoxicity when incubated for more than 20 days; however, phytotoxic effects were observed at shorter incubation periods (0 and 10 days). After 20 days of incubation, both the fresh and dry mass of the plants increased proportionally with the rise in waste concentration. Greenhouse experiments further revealed that yellow mealworm frass enhanced stem diameter, fresh and dry mass, net photosynthesis, and water use efficiency of tomato plants. These findings underscore the potential of yellow mealworm frass as an effective organic fertilizer in agriculture.