Bone meal, blood meal, meat and bone meal, and feather meal are waste products produced by slaughterhouses. They are all permissible for use in organic crop production and are good sources for nutrient fertilization. Slaughterhouse meals are also very sustainable options because they make use of waste products.

Bone meal is animal or fish bones that have been ground into fine and coarse powders that are mixed together. Bone meal is used as a slow-release phosphorus amendment and also adds protein and calcium to the soil. The more finely ground the bone meal is, the faster plants will be able to utilize the nutrients it releases. Bone meal can be costly and is mainly used in small gardens as opposed to large farms. As a substitute for rock phosphate, bone meal is easier to obtain, easier to spread, and has higher nutrient availability.

The ratios of nitrogen, phosphorus, and potassium (N-P-K) in bone meal vary depending on the source, it is generally listed as 1-11-0 or 3-30-38. Bone meal is not a significant source of nitrogen for plants, but it provides significant amounts of phosphorus.

Acidic soil with a pH above 7.0 will inhibit phosphorus release from bone meal amendments. Before applying bone meal, pH must be tested and corrected. Once corrected, the bone meal can be mixed in with the soil prior to planting. Bone meal can also be used to balance soil that has accumulated too much nitrogen.

Blood meal is a high nitrogen powder made from drying blood. Blood meal is one of the most nitrogen-rich organic amendments and contains approximately 13.25% nitrogen, 1.0% phosphorus, and 0.6% potassium. Hemoglobin (blood) is the main component in blood meal. Hemoglobin contains iron, making blood meal an ideal fertilizer for crops that thrive with the addition of the micronutrient.

Most crops are highly sensitive to iron deficiency, with the exception of wheat, so the increased iron availability is an added benefit. Some caution that the nitrogen supplied by blood meal is too readily available to plants and therefore is not used as efficiently as nitrogen from other organic sources.

Blood meal can acidify soil so pH should be monitored. Since blood meal is water-soluble it can act fast to correct nitrogen deficiencies and feed plants for 6-8 weeks after a single application. Blood meal can be applied by mixing with soil prior to planting, or by dissolving in water to apply to established plants. Blood meal can also be spread in gardens to deter pests such as rabbits.

Meat and bone meal contains both the flesh and bone of slaughterhouse livestock. It is sometimes also called processed animal protein. To make meat and bone meal, the slaughterhouse waste from animals is defatted, cooked, sterilized, ground, and then sifted. Meat and bone meal contains approximately 8% nitrogen, 5% phosphorus, and 10% calcium, as opposed to bone meal alone which does not have any significant nitrogen content. Studies have shown that when meat and bone meal are applied together with blood meal, populations of beneficial soil microbes increased, which is very beneficial to increasing soil fertility and nutrient availability.

If meat and bone meal is used to meet the nitrogen requirements of a crop, the soil will have residual phosphorus levels that will be sufficient for the following year’s crop. That means the following crop will need only nitrogen, potassium, and micronutrient amendments applied and the application of more phosphorus should be avoided.

Feather meal, which contains approximately 12% nitrogen may be used in place of blood meal. It is another waste product from slaughterhouses and is produced by heating and grinding poultry feathers in a pressurized system. Since feather meal is not water-soluble, it releases nitrogen more slowly than blood meal and its nutrients are less accessible by plants.

Blood meal and feather meal can both be used as a compost activator to boost microorganism activity balance compost that is high in carbon and decomposing too slowly.