This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The use of bones as a manure dates from the earliest times, and has become more extensive than ever. Between 45,000 and 60,000 tons of bones in various forms have been imported annually in recent years from the East Indies, the Argentine, Brazil, Morocco, Egypt, and the Continent. In addition to this it is computed that about 60,000 tons of bones are also available annually in the United Kingdom. This would bring the manurial consumption of bones up to about 100,000 tons per annum.
In a natural state bones are crushed into various sizes, and in the form of bone meal are very popular with gardeners. A ton of bone ash contains from 800 to 900 lb. of phosphates; while 1 ton of dissolved bones, and 1 ton of steamed bones contains from 300 to 600 lb. of phosphates. Bone flour is also a valuable phosphatic manure, containing over 300 lb. of phosphates in 1 ton, and also yielding up a small quantity of nitrogen. Dissolved bones also yield up even a larger supply of nitrogen.