The degree of hydrolysis of meat and bone meals fertilizers drives carbon mineralisation and the availability of nitrogen and phosphorus in soil

Meat and bone meals (MBMs) are animal by-products that can be recycled in agriculture as organic fertilizers following appropriate sanitization treatments. However, nutrients bioavailability depends on soil mineralisation processes and often does not match crops’ nutrient demand. Alkaline thermobaric hydrolysis (ATH) is a scalable physico-chemical process commonly applied to animal biomasses to enhance nutrient availability, yet its effects on the fertilising potential of MBMs remains poorly understood. In this study, two ATH protocols were applied to an MBM to obtain products with different degrees of hydrolysis (DH). The resulting fertilizers were characterized in term of DH and subsequently incubated into the soil to assess organic carbon (C) mineralisation and nitrogen (N) and phosphorous (P) availability. Increasing ATH intensity resulted in higher DH values, ranging from 7 to 8% in non-hydrolysed MBM to 13-15% and 40-60% in low- and high-hydrolysed MBMs, respectively. Organic C mineralisation was not significantly affected by ATH treatment. In contrast, soil N availability increased with increasing DH, with potentially mineralizable N rising from 37% in the non-hydrolysed MBM to 48-52% in the hydrolysed products. Soil available P, however, was not enhanced by the hydrolytic process. These findings demonstrate that alkaline thermobaric hydrolysis can modulate nutrient release from MBMs, primarily increasing N availability, while having limited effects on organic C mineralisation and P availability. Overall, the results suggest that the degree of hydrolysis may influence nutrient release dynamics and should be considered when developing MBM-based fertilizers with targeted agronomic properties.