How do beef cattle farm characteristics impact manure properties? Implications for agronomic circularization and sustainability

The pursuit of a circular economy in the meat production sector requires management of manure resources, which limits environmental contamination and maximizes fertilizing value. However, it is not known how easily identifiable farm characteristics may influence solid manure chemical properties, ostensibly leading to better standardization of manure management in the sector. In this study, we analysed cattle manure from 36 Spanish farms representing the most common productive models. Based on the categorizations of farm type (fattening and mixed), bedding type (straw, other, none) and farm size, our findings reveal significant variability in manure composition. N contents ranged from 0.35% to 3.87%, significantly influenced by farm type (p < 0.05), with fattening cattle manure having the greatest N contents. P and K contents were not affected by the studied categorical parameters, whereas P contents varied from 0.7% to 4.0%, and K contents varied from 0.28% to 3.2%, with the largest variabilities associated with farm size. Eight farms exceeded permitted limits for EU Fertilizing Products for Zn, but this could not be attributed to known farm characteristics. Also, one farm exceeded Ni limits, and one farm Hg limits. For use as fertilizer, the average estimated emissions avoidance from the manufacture of synthetic fertilizers was calculated to be 32.57 kg CO₂eq tonne manure⁻¹. Due to the high variability of manure properties based on the key farm characteristics, the results underscore the need for individual characterizations of manures by farmers or waste managers, or the identification and consideration of additional covariables influencing manure properties.