Several agro-industrial, livestock, and food wastes can be recycled to create biofertilizers. This diversity of raw materials can result in nutritional imbalance and an increase in heavy metal content, which could make the final product unfeasible. Thus, the chemical characterization of the raw materials and their influence on the sustainable and safe production of biofertilizers need to be better understood. In this context, the objective of the present study was to evaluate the chemical characteristics of agro-industrial residues used in the manufacture of an aerobic liquid biofertilizer. We analyzed the macronutrient, micronutrient, and trace metal contents of seven waste products used as raw materials to create a biofertilizer. In addition, a survey of secondary biofertilizer data from different residues was carried out that showed great heterogeneity in the chemical compositions of these residues, which has a direct impact on the agronomic efficiency of these biofertilizers. The characterization revealed that some materials may be contaminants of the soil, due to high levels of trace metals, especially cadmium. We conclude that the generation of detailed inventories, such as those of the nutrient and heavy metal contents of the raw materials and biofertilizers produced, is indispensable for the correct recommendation of biologically-based inputs in agriculture.

Root-knot nematode (RKN) is a serious threat to crops worldwide due to the difficulty in controlling it and the limited eco-friendly alternatives to deal with the biotic stress it causes. In the present work, water-extractable fractions obtained from vermicompost (WSFv), vermicompost enriched with Trichoderma asperellum (WSFta) and T. virens (WSFtv) were tested as biotechnological tools to reduce the impacts of RKN on gas exchange, water use efficiency (WUE) and nutrient concentration in tomato and bell pepper plants. The plants were infected with 5000 eggs and eventual J2 of RKN and then treated with the water-extractable fractions for seven weeks. It was observed that the addition of WSFta, WSFtv and WSFv increased the CO₂ assimilation, stomatal conductance and WUE in the tomato plants. In the bell pepper plants, WSFta, WSFtv, WSFv increased the stomatal conductance, while WUE was higher in the treatment with WSFtv. In fact, the parameters associated with the gas exchange were usually higher in the bell pepper than in the tomato plants. Overall, higher contents of N, Mg, B and Mn were detected when the extracts were applied in both bell pepper and tomato plants. The application of the water-extractable fractions, inoculated or not with Trichoderma, attenuates the RKN damage on the gas exchange parameters and successfully enhanced the nutrient concentration in the infected tomato and bell pepper plants, showing that it could be an important and promising tool for reducing the damage caused by this pathogen. We suggest that both the tomato and pepper plants can cope with the dilemma between growth and stress response via stomata regulation that are modulated by the WSF and Trichoderma.