Guano

Guano (derived from the Peruvian word huano, ‘dung’) is the excrementitious deposit of certain sea-fowl, which was found in immense quantities on certain coasts and islands where the climate is dry and free from rain. Although the use of guano as a manure is comparatively recent in Britain and in Europe, its value in agriculture was well known to the Peruvians long before the coming of the Spaniards. Alexander von Humboldt first brought specimens of guano to Europe in 1804, and sent them to Fourcroy, Vanquelin, and Klaproth, the best analytical chemists of the day.

The commercial value of guano depends almost entirely upon the amount of decomposition to which it has been subjected by the action of the atmosphere, the value consisting as it does essentially of nitrogenous and phosphatic compounds, the former being chiefly ammonia salts derived from the decomposition of the uric acid and urates which exist in the fresh excrement. The ammoniacal portion of these deposits, and some of the phosphates, are tolerably soluble in water, and are readily washed away by rain. There are three classes of guanos : (1) those which have suffered little by atmospheric action, and which retain nearly the whole of their original constituents, such as the Angamos and Peruvian guanos; (2) those which have lost a considerable portion of their soluble constituents, but remain rich in their less soluble constituents—the phosphates of lime and magnesia, such as the Ichaboe, Bolivian, and Chilian guanos; (3) those which have lost nearly all their ammonia, and contain but little more than the earthy phosphates of the animal deposit—many being further largely contaminated with sand. In the last class must be placed the various African guanos (excepting that from Ichaboe), West Indian guano, Kuria Muria (islands off the coast of Arabia) guano, Sombrero guano, Patagonian guano, Shark’s Bay guano (from Australia), &c.

Most of the so-called Peruvian guano has been obtained from the Chincha Islands off the coast of Peru. The following table represents the mean of 78 samples of Peruvian guanos :

The following table gives the mean of several analyses of the inferior kinds of guano, the first four belonging to the second class and the remaining three to the third class :

The nitrogen in these analyses is calculated as ammonia for the purpose of comparison. In reality it exists in various forms of combination—viz. as uric acid, urea occasionally, urate, oxalate, hydrochlorate, phosphate, &c., of ammonia, other urates, Guanin (q.v.), and undefined nitrogenous compounds. Hence, as may be inferred, a complete analysis of guano is a work of very considerable labour; but, as its agricultural value depends mainly on the quantities of ammonia, soluble and insoluble phosphates, and alkaline salts which it contains, such analyses as those we have given are sufficient for practical purposes, and they are easily made.

If the value of a manure be calculated, as is done by Boussingault and other chemists, according to the amount of nitrogen which it contains, one ton of good Peruvian guano is equal to 33½ tons of farmyard manure, 20 tons of horse-dung, 38½ tons of cow-dung, 22½ tons of pig-dung, or 14½ tons of human excrement.

The introduction of guano into Britain as a manure is comparatively recent. In 1840 only 20 casks of it were imported. In 1841 Lord Derby spoke strongly in its recommendation at a meeting of the Agricultural Society; and from that time it came rapidly into use. In 1850 the import was 116,925 tons; in 1870, 280,311 tons; but in 1880 it had fallen to 80,497 tons; and from 1885 to 1888 it had still further decreased from 25,000 to 17,000 tons. Its value as a fertiliser has been so much appreciated, and its use so extensive, that it is gradually going out of the market owing to the diminution of supplies, its place being taken by various artificial substitutes (see MANURE). See J. C. Nesbit’s pamphlet, History and Properties of Natural Guanos (new ed. 1860).