Guano

Guano, the droppings of fish-eating birds on rainless or nearly rainless sea-coasts. Besides penguins, cormorants, and other birds, seals contribute to the formation of true guano, and the name "bat-guano" has been used for the accumulated dung of these animals which occurs in many caverns in various quarters of the globe. Humboldt brought guano from the Chincha Islands of Peru to Europe in 1804, and when Liebig called attention to its value as a manure in 1840 it became an important article of trade; but the South American sources of the supply have been largely exhausted It is also obtained from the Angra Pequena islands, off the south-west coast of Africa, and from the Kuria-Muria islands, off the coast of Muscat. The value of guano as manure depends upon its richness in phosphates and nitrogen, the latter occurring as urates and ammonium salts which would be dissolved out by rain. It also contains an alkaloid guanine (C₅H₆N₅O). The nitrogen, reckoned as "potential ammonia," varies from 1 to 25 per cent., the phosphate from 6 to 56, and moisture from 11 to 17 per cent. Guano is an actively stimulating manure, tending to cause a great production of foliage and therefore useful for grass crops; but, mixed with superphosphate of lime, it is also valuable for flowering plants and roots. It is sold by analysis, at about £13 per ton for the best qualities.