Heterogeneity in the Chemical Composition of Biofertilizers, Potential Agronomic Use, and Heavy Metal Contents of Different Agro-Industrial Wastes

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.