Production of biochar derived from guinea pig manure as a soil amendment in high Andean and coastal acidic soils in Peru: agronomic potential and cost analysis for sustainable circularity

Introduction The valorization of local resources, such as guinea pig manure, allows traditional inputs to be transformed into more stable products with higher added value, such as biochar, rather than being used as raw manure. Methods This study evaluated the physicochemical properties, toxicity, and neutralizing capacity of biochar obtained from guinea pig manure, produced by open pyrolysis in a pyrolytic oven in Huancayo, Junin, Peru. Fresh manure was also characterized prior to pyrolysis, and its median lethal dose was determined. Results The results indicated that guinea pig manure had an approximate volume of 2,883.99 cm 3 in an uncompacted state and 2,205.41 cm 3 in a compacted state, with densities of 0.293 and 0.380 kg/cm 3 , respectively. Guinea pig manure biochar has high N, P, and K contents, as well as a significant percentage of ash (34.6%) and fixed carbon (37.9%). Its alkaline pH (9.17), high cation exchange capacity (48.8 meq/100 g), and high organic matter content (62%) suggest its potential for improving acidic soils. It also has a considerable moisture content (34.8%) and microelements such as Mg, Cu, Ca, and Zn. In economic terms, the production of 1 ton of guinea pig manure has an estimated cost of 231.23 soles, while the sale price of biochar reaches 3,515.31 soles per ton, demonstrating its high added value. Discussion Biochar derived from guinea pig manure has a superior nutritional profile compared to biochars obtained from plant biomass, making it a viable alternative for agriculture. Its application, however, must take into account specific safety tests for each crop to ensure both safety and effectiveness.