GUANO, gwa'no (Spanish guano huano, from Peruvian huanu, dung), is the name for deposits of the partially decomposed and dry excrementitious matter of birds, especially sea birds, as those that frequent coast islands. It is highly valued as a fertilizer. Deposits from sea-birds are found wherever there is good feeding-ground in the neighborhood of un frequented islands and rocky cliffs. All the notable guano deposits exist in the hottest and driest parts of the tropics, as on the islands of the South Pacific Ocean. The most important of all were the deposits on the Chincha Islands off the coast of Peru, which for years yielded a considerable revenue, but were exhausted. The guano there was from 60 to 100 feet in thickness, and was entirely due to the droppings, accumulated for many ages, of the innumerable sea-birds which make these islands their rest ing-place and breeding-ground. The excrement rapidly dries by exposure to the sun in a region where the rainfall is slight, and thus the soluble salts of which guano to a great extent consists are retained. Peruvian guano is the best known, but in Patagonia, various points of Bolivia. Mexico, Chile, Malden Island and numerous other Pacific islands new deposits have been opened up as the older were exhausted.
Guano varies extremely in composition, even in the same deposit considerable differences will be found; and deposits from different localities show great difference in chemical•content. Some consist mainly of phosphate of calcium and other fixed salts, while others contain much volatile matter, with a large proportion of am monia. Peruvian guano is a very light, dry, non-cohesive, pale-yellow powder, with a char acteristic ammoniacal odor, and sometimes con tains lumps, made up of different salts. It is a very complex mixture, containing the urate of ammonium, the oxalates of ammonium and cal cium, the phosphates of sodium, ammonium, calcium and magnesium, the sulphates of potas sium, sodium and ammonium, the chlorides of sodium and ammonium, and the carbonate of calcium. There is always some moisture, or
ganic matter of different kinds, sand from the rock on which the deposit lies, and this is an impediment to marketing. The ingredients which are especially prized are the ammoniacal salts, the phosphoric acid, in combination with the alkalies and alkaline earths, and the alkalies themselves, particularly the potash. It is the remarkable abundance of these constituents and their fine intermixture which caused Peruvian guano to be so much esteemed as a manure. The deposits often contained almost all the inorganic matter required by a plant, and that in a highly available form, so that it was one of the best of all fertilizing agents for different crops. As the supply became reduced, however, it was found to be very irregular in composition. Its use as a manure was known to the native Peruvians centuries ago, but no attention was paid to the accounts by modern travelers of its wonderful efficacy until A. von Humboldt took some to Europe, in 1804, and had it analyzed. It was not exported on a large scale till about 1850, and from that time the quantity sent to foreign countries, including large shipments to the United States, was very great, but the scien tific study of fertilizers and utilization of local materials has much reduced the demand, and the supply is also much diminished.
As a substitute for ordinary guano, what is known as fish-guano has been in use for a con siderable number of years. This consists essen tially of fish and fish offal dried and powdered. In the case of oily fish, such as herrings, it is customary to extract as much of the oil as possible before the operation of powdering; and it will thus be understood that different kinds of fish differ greatly as regards their value for manurial purposes. But all sorts of fish guano contain a large percentage of ammonia and phosphate of lime, and are thus valuable as fertilizers (q.v.), Consult Coker, 'Fisheries and Guano Industry of Peru (in Bureau of Fish eries Bull. 8, Pt. 1, 1908).