Biochar from guinea pig manure as soil amendment: agronomic potential and cost analysis for sustainable agricultural circularity

The valorization of guinea pig manure transforms a traditional input into a stable, high-value product like biochar. This study evaluated the physicochemical characteristics, toxicity, and neutralizing capacity of biochar produced by open pyrolysis in Huancayo, Junín, Peru. Fresh manure was also characterized before pyrolysis, and its median lethal dose was determined. Results showed that uncompacted manure had a volume of 2,883.99 cm³ (0.293 kg/cm³), and compacted manure 2,205.41 cm³ (0.380 kg/cm³). The resulting biochar had high contents of nitrogen, phosphorus, potassium, ash (34.6%), and fixed carbon (37.9%), along with an alkaline pH (9.07), high cation exchange capacity (48.8 meq/100g), and elevated organic matter (62%), indicating its potential to improve acidic soils. Moisture content (34.8%) and the presence of microelements (Mg, Cu, Ca, Zn) also suggest agronomic benefits. Economically, producing one ton of biochar from guinea pig manure costs approximately 231.23 soles, while its market value is 3,515.31 soles per ton, reflecting significant added value. Overall, guinea pig manure-derived biochar presents a promising alternative to plant-based biochars due to its superior nutrient profile. Nonetheless, crop-specific safety evaluations are essential prior to its agricultural use to ensure both effectiveness and safety.