FISH-GUANO. The organic fertiliser commonly known as Fish-guano may be shortly defined as fish dried and ground to powder. The value of fish as a fertiliser is universally admitted, and is evidenced by the eagerness shown by farmers, who reside in districts where fish can be easily and cheaply obtained, in acquiring and applying it to their land. Mussels, five-fingers or starfish, herrings, and particularly sprats may be instanced as the fish most generally used in this way. The inconvenience and expense arising from this mode of application to the soil, on account of the bulky as well as the unpleasant nature of the material, is obvious, the non-fertilising moisture alone amounting to between 60 and 80 per cent., and by so much enhancing the cost of general haulage. The desirability of converting raw fish into a concentrated and portable powder comparatively free from moisture was first practically realised only shortly before 1862 by M. Rohart, whose product was obtained from the refuse of the Norwegian cod-fisheries by drying the heads and backbones of the codfish upon heated floors after they had been sun-dried on the rocks, and subsequently grinding them between millstones to a floury powder.
Of late years fish-guano has grown rapidly in favour among agriculturists, a preference based doubtless upon its merits as a fertiliser, and probably also due to its similarity both as regards origin, analysis, and effect to Peruvian guano. The supplies of Peruvian guano, as is now generally known, are practically exhausted, the imports into the United Kingdom having fallen from about 300,000 tons per annum in years gone by to about 17,000 tons in 1888. Not only in quantity is Peruvian guano deteriorating, but also in quality, the ammonia, for example, found by Voelcker in 1864 being 18.62, whereas in 1889 the very best shows only 9.50, and others vary from 6.50 per cent. down to as low as 3 per cent.
In some quarters nitrate of soda has been named as the probable substitute for Peruvian guano; but, although its supplies are at present enormous, the character, composition, and action upon the soil are entirely different, one being of a mineral and the other of an organic origin. Fish-guano may be held to contain the fish with its natural properties of nitrogen and phosphoric acid in full; while Peruvian guano, which is the accumulation during ages of the excrement of birds whose main food has been fish, must have suffered by the action upon the fish of the digestive organs of the birds, as well as the effect of the weather upon the deposits. Fish-guano may therefore be considered as the best substitute for the failing supplies of Peruvian guano. Another advantage is the fact that the available supplies of fish in Norway, Canada, Newfoundland, and elsewhere are practically inexhaustible. Fish-guano, according to the fish from which it is made, analyses from 9 to 14 per cent. of ammonia, and from 13 to 32 per cent. of phosphate of lime. At the present time the selling price per ton is fixed, as regards the ammonia it contains, by the ruling market price per unit of that ingredient in nitrate of soda, and, as regards the phosphate of lime, by the price of bone and Calcutta bone-meal. The market value of fish-guano varies, according to the analyses, from about £6 to £8 per ton weight. One ton of fish-guano is said to be equal in chemical effect to seventeen times its weight in farmyard manure.
Of the most generally known fish-guano there may be said to be four kinds. There is the 'raw' guano made in Christiansund and the Lofodens, upon M. Rohart's principle, which is used principally in Germany. There is also a guano made in London, Hull, and elsewhere, from fish which has been condemned by the authorities as unfit for human food. This description, naturally, embraces fish of all kinds and sizes, its great drawback being the large quantity of oil left in the guano, the presence of which element is prejudicial to any fertiliser. By far the largest quantity of fish-guano is manufactured in various parts of Norway, but principally at Brettesnoes, in the Lofodens, by Jensen & Co., who make as much as 5000 tons per annum. This guano is made from the heads and backs of the codfish, and also from the herring. In both instances the 'raw stuff' is artificially dried and ground, much time being saved by this process, instead of waiting some months until the bones were sufficiently dried by the sun. To make 1000 tons of cod-guano 7,000,000 heads are necessary, and to obtain these 50,000 tons weight of fish have to be caught. The oil found in this guano is practically nil. The 'herring-guano' is obtained by extracting the oil and moisture by means of pressure from the herrings; the 'cake' thus obtained is then ground in the ordinary way by means of disintegrators, the result being a fine powder of high manurial value. Guano obtained from the cod analyses about 10 per cent. of ammonia and 30 per cent. phosphates, the latter high figure being due to the large predominance of bone over fleshy or nitrogenous matter. The contrary is the case in the herring-guano, in which the fleshy matter is very much greater than the bony substance, the analysis being about 13 per cent. each of ammonia and phosphate. Guano is also made in Canada and elsewhere from lobster and crab shells, and this is stated to be a valuable manure for garden purposes. The annual production of fish-guano is estimated at the present time at 15,000 tons, including that made in England, Scotland, Norway, Sweden, Newfoundland, Nova Scotia, and the United States of America. For Rock-guano, see APATITE.