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.
Blood may be regarded as a complete fertilizer, as it contains not only nitrogen (from 2 1/2 to 5 per cent in a fresh state, and from 6 to 14 per cent in a dried state) but is also rich in all other plant foods, as may be seen by the following analysis of the ash: -
Calcium and magnesium phosphates ...
Oxide and phosphate of iron ...
Sodium chloride (common salt)
Calcium sulphate (gypsum)
It will be observed that common salt constitutes more than half the weight of blood ash. When fresh blood can be obtained from slaughter houses it is best mixed with large quantities of soil and then allowed to "mature" in a heap until wanted for use. Dried blood is a more concentrated source of nitrogen than fresh blood, as water has been eliminated. It is a good fertilizer for all well-worked soils, and may be regarded as specially valuable for Potatoes, Cabbage crops, Vines, and fruit.