Feedstock and transformation processes drive the valorization of agro-livestock waste for a circular agriculture

Le résumé fourni par la source

Modern agriculture faces growing challenges from soil degradation, climate variability, and reliance on synthetic fertilizers, threatening long-term productivity and food security. Circular economy strategies, particularly the valorization of agro-livestock residues into bio-based soil amendments, provide solutions for restoring soil health and reducing environmental impacts. This study offers a comprehensive assessment of contrasting organic materials, including lignocellulosic composts, selectively collected composts, compost tea, anaerobic digestates, cattle slurry, and biochars from diverse feedstocks and pyrolysis temperatures. Commercial composts and biochars were included as benchmarks. All materials underwent physicochemical, elemental, and thermogravimetric characterization, trace element analysis, and phytotoxicity testing with barley (Hordeum vulgare) germination assays, a globally important crop recognized as a sensitive phytotoxicity indicator. Compost- and digestate-based amendments displayed agronomically beneficial traits, including high nutrient levels (N, P, K, Ca, Mg), near-neutral pH, and abundant labile organic matter, supporting microbial activity and nutrient availability. Correlation analyses revealed links between ash content and macronutrients, and between pyrolysis conditions, carbon stability, and surface area. Lignocellulosic biochars showed optimal carbon content, recalcitrance, and nutrient balance without exceeding regulatory thresholds for potentially toxic elements. By contrast, wool- and digestate-derived biochars contained elevated Zn, Cd, and Cr, posing phytotoxic risks. All biochars supported germination except wool biochar at 500 °C, which fully inhibited it. Similarly, leachates from composts and digestates reduced germination, likely due to salinity, though biochar co-application mitigated these effects. Overall, results highlight the complementary roles of composts, digestates, and biochars in regenerative agriculture, and emphasize feedstock selection, pyrolysis optimization, and amendment blending to improve agronomic performance.

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