Organic fertilisers are produced in large quantities as by-products of the meat export industry, slaughter houses, and soap manufacture. Typical products are bone meal or bone dust containing water-insoluble phosphorus and some nitrogen; dried blood, a good organic source of nitrogen; and tankage, a powder obtained from cooking, drying, and grinding animal refuse of heterogeneous origin. Tankage contains water-insoluble nitrogen and phosphorus. These organic fertilisers of animal origin are mainly used in commercial market gardens, orchards, and by private gardeners. They may be incorporated in proprietary mixtures, but commonly are applied as so called “Blood and Bone”, a mixture of bone dust and dried blood or tankage and dried blood. Blood and bone contains about 4–7 per cent nitrogen and 10–13 per cent phosphorus. Market gardeners commonly apply 1½-2 tons of blood and bone per acre to leafy vegetables. This heavy rate of application is commonly followed by side dressings of soluble inorganic nitrogenous fertilisers during the growing season. Tomatoes, pumpkins, and cucumber also receive large quantities of organic fertilisers.
Small amounts of organic fertilisers are incorporated into proprietary mixtures which are sold to farmers for the manuring of crops and, to a lesser extent, for topdressing of pastures. The use of these manures in farming is not recommended. A vigorous export trade with organic manures has developed in recent years.