Bone and meat meal: fertilizers from slaughter waste

Bone meal and meat meal are made from slaughterhouse waste, and sometimes from fish processing. It is estimated that on average 30% of the live weight of a slaughtered animal is represented by materials that cannot be used for human nutrition. Among these, in addition to the portions of meat that are less valuable or otherwise unsuitable for human consumption, are fat, bones, various organs, blood and feathers.

Once widely used as supplements in animal nutrition and now subject to severe restrictions for such use, as a result of cases of BSE (Bovine Spongiform Encephalopathy) transmitted to humans in the late nineties, bone and meat meals have emerged significantly in the production of organic and organo-mineral fertilizers, thanks to interesting Nitrogen, Phosphorus and Calcium content.

The use of these two by-products as fertilizers, combined with their use in an incinerator for energy purposes and the production of biogas, allows the possibility to return to the soil part of what has been subtracted for the production of food (fodder and corn) used in husbandry.

Fertilizers made from bone meal, meat meal or both are allowed for use in organic agriculture.

Within the European Union, animal by-products with the potential to be transformed into fertilizers are subdivided by Reg.  (EC) No. 1069/2009 into three hazard classes, linked to the possibility that these materials may transmit spongiform encephalopathies. Slaughter waste from which bone and meat meals are obtained, for use as fertilizers, fall into classes 2 and 3, those of low danger. These materials must be sterilized at high temperature and pressure (class 2) or pasteurized (class 3) before being ground.

Bone meal is obtained by grinding animal bones more or less finely, to which fish bones are sometimes added, and drying them. This last process can be carried out in different ways, which affects the bioavailability of nutrients for plants when bone meal is used as fertilizer.

Before being ground, bones may or may not undergo a degreasing and degelatinizing process, which affects the nutritional content of the finished product. Essentially it becomes an NP fertilizer, with a heavier ration of Phosphorus that varies, however, depending on the starting material and the processes applied. Indicatively, if the bones are degelatinized the ration ranges from 1:13 — 2:18, or 4:12 in the absence of this pre-treatment. Since natural phosphate resources are limited, the reuse of Phosphorus within the food system is extremely important to promote the sustainability of productions.

Bone meal also provides variable but high amounts of Calcium (more than 20% with dry matter). This makes it particularly interesting for use in soils with an acidic pH, which need correction.

Also known as meat scraps, meat meal is obtained from the processing residue of slaughtered cattle, sheep and pigs, thermally treated as previously described to ensure health safety, then dried and ground.  Compared to bone meal, meat meal has a more varied composition and is particularly higher in nitrogen content.

Often the two products are used as a mixture in the same fertilizer to obtain the best composition. It should be noted that meat and bone meals also contain various organic compounds (amino acids, peptides, especially proteins, in addition to humic and fulvic carbon), which can optimize the C/N ratio, improve the microbial activity of the soils on which they are distributed, and gradually release their nutrients over time.

The table below, taken from the publication Meat and Bone Meal (modified), shows the average composition (and in brackets the maximum and minimum values) of the macro and meso-elements of bone meal, meat meal and mixed bone and meat meal (values expressed in % in dry matter).

Meat and bone meals are involved in the formulation of numerous Agribios Italiana products, namely:

Organo-mineral fertilizers: Biocomplex 5.15.5, Agriazoto 300, Agrical Plus, Dorado, Superprimo, Ortofrutta, Agricomplex 10.5.15.

Conditioners and correctives: Agriorganico 7%, Biodieci, Agricars Super, Superoro.

Organic fertilizers: Agrimyz 77, Nemakil 330.

Liquid fertilizers: Agristimol (liquid meat meal in suspension).

Among the products mentioned, Superoro deserves special mention, exclusively made from bone and meat meal.  Superoro’s characteristics and effects on the crops are utterly special and cannot be compared with those of other fertilizers with a similar qualification. The Nitrogen and Phosphorus in Superoro are linked to protein molecules and made available to plants gradually, at pace synchronized with the nutritional needs of crops. The nutrients contained are not leached and incapable of dissolving in the soil, such as with mineral fertilizers, and they promote exceptional biological activity. Loss of nutrients caused by leaching is reduced, with the nitric nitrogen produced corresponding with the amount used by the vegetation distribution. The primary nutritional needs of crops are provided by amino acids, then peptides and finally proteins. The same considerations can also be extended to phosphorus. The increased activity of microorganisms caused by the use of Superoro is also reflected in the solubilization of the bone phosphates contained, enhancing the phosphorus availability to plants.