Its Action as a Manure.
Next to farmyard manure, guano may be regarded as the most "general" of all the commonly used manures; for in addition to nitrogen, phosphoric acid, and potash, it contains nearly all the other plant ingredients, such as lime, magnesia, &c. Its special value as a manure, however, does not merely consist in the amount of valuable plant-food it contains. Like farmyard manure, it owes much of its characteristic action to the state of the intimate mixture of its manurial constituents, and also, as has already been pointed out, to the fact that it contains those constituents in a great variety of chemical forms, each of which differs in its solubility, and consequently availability for the plant's needs. Take, for example, the great number of different forms of nitrogen it contains. Some are in the condition in which plants can immediately absorb them, while the rest are in a series of less and less available forms, which, however, are gradually converted into available forms as the plant requires them. Like farmyard manure, again, it may be applied with almost equally good results to all kinds of crops and on all kinds of soils. We have in guano, in short, an admirable example of the value of applying our manurial ingredients in different forms. That this is no mere theory is abundantly proved by the large number of different experiments which have in the past been carried out with guano, more especially the well-known experiments made by Grouven, the German chemist. In those well-known experiments, guano was tested against a large variety of different fertilisers, and the tests were so arranged that in most cases the amounts of nitrogen, phosphoric acid, and potash were the same in the other manures used. In short, these experiments prove in a very striking manner that a manure artificially made up out of most valuable fertilisers, such as nitrate of soda, sulphate of ammonia, superphosphate, &c., so as to closely resemble in its composition guano, is by no means similar in its effects to the genuine article. As in farmyard manure, so in guano: we must look to the complexity of the composition of both these fertilisers in order to fully estimate their worth. There is in the action of both manures much that we cannot explain, or even, as yet, understand. The action of guano is merely one of many problems in the science of manuring which illustrate how unsatisfactory, despite the great amount of research already carried out, is our knowledge of this most important department of agriculture.[197]
Proportion of fertilising Constituents in Guano.
Guano must be regarded as a nitrogenous and phosphatic manure, as the quantity of potash it generally contains is small. In many soils, more especially in such a country as Scotland, this deficiency in potash is not of so much importance, as the value of potash as an artificial manure is less than is the case with the other two ingredients. In soils, however, lacking potash, guano ought to be supplemented with some potash manure. With regard to the nitrogen and phosphoric acid, we may ask if these two constituents are in the best proportions. This question does not admit of a direct answer. In the first place, the proportion in which these two ingredients are present is variable. In the old rich Peruvian guanos, as we have above shown, the nitrogen was more abundant than is the case at present. Such guanos, it was found, were best supplemented with phosphatic manure when applied to the field. In the "equalised" and "dissolved" guanos, which are now so largely sold, manufacturers attempt to adjust the percentage of nitrogen and phosphoric acid to what is considered the best proportion in most cases. As, however, we have again and again to point out, regard must be had both to the soil and the crop in determining what is the best proportion of the manurial ingredients in a manure. For cereals it may be well supplemented by nitrogenous manures, while for roots it may be well supplemented by phosphatic manures.
Mode of Application.
Like all manures, it is desirable to apply it in as fine a condition as possible, so as to ensure as thorough a mixture with the soil-particles as practicable. In order, furthermore, to prevent any risk of loss through volatilisation of the ammonia, as well as to ensure even distribution, it is best applied mixed with dry earth, ashes, sand, or some other substance,—not lime, however. The custom of applying along with the guano common salt, has been proved by numerous experiments to be highly beneficial to the action of the guano as a manure. The exact nature of the action of salt as an adjunct to manures is a point which has elicited much discussion. Its action is probably to be ascribed to a number of causes. For one thing, it probably acts as an antiseptic in retarding the fermentative action which has a tendency to go on so rapidly in such manures as guano. It further increases the power of the manure to attract moisture from the air—a most important property in the case of drought. Some experiments by Dr Voelcker illustrate this in a striking manner. Two lots of guano—one pure and one mixed with salt—were exposed to the action of the air for a month, and were then tested as to the amount of water they contained, when it was found that the lot containing the salt had absorbed 2 per cent more water than the other.
Much stress has been laid on the importance of having the guano buried a certain depth in the soil; and many experiments have been carried out to prove how much better it acts when so applied. This is probably due to the prevention of any loss of volatile ammonia, and the mixture of the manure with the soil-particles before it comes in contact with the plant-roots. This last precaution is an important one, for it has been found that the raw material is apt to have a bad effect on the seed or the plant's roots. This has been found to be especially the case in regard to potatoes, the quality of which has been found to suffer when the guano is brought into direct contact with the tubers. As guano is a manure which is speedily available, it is desirable to apply it as shortly before it is required by the plant as possible. It is therefore generally best applied in spring, shortly before seed-time, or indeed at the same time. Where farmyard manure is used, the guano has been recommended to be used as a top-dressing in small quantities. In the majority of cases it will be advisable, however, not to apply it as a top-dressing, for the various reasons above-mentioned.
Quantity to be used.
As to the quantity to be used, this of course will depend on the soil, the crop, and the amount and nature of the other manures employed: 1 to 4 cwt. per acre have been the usual limits, but even heavier dressings have been commonly resorted to, especially in Scotland, where 6 to 8 or even 9 cwt. for turnips are often used. Sir J. B. Lawes and Sir James Caird long ago, shortly after the introduction of guano, estimated, from the experiments they carried out, that the application of 2 cwt. per acre to the wheat crop gave an increase of 8 to 9 bushels in grain, and added a fourth to the quantity of straw. The former authority recommends 2 to 3 cwt. per acre for wheat, to be sown broadcast and harrowed into the land before sowing the seed. We have already stated that it may be used in all soils and for all kinds of crops. While this is so, it has been found to have specially favourable results when applied to the turnip crop, when it may be used in larger quantities than in the case of cereals. When applied to the turnip crop, it is well to use the more phosphatic guanos or to supplement it with superphosphates. By applying it in two lots, the larger portion before seed-time and the rest between the drills after the turnips are up, excellent results have been obtained. It has also proved an admirable manure for mangels. On the whole, it gives best results on heavy soils and in a dampish climate.
Adulteration of Guano.
Probably no artificial manure has been subjected to greater adulteration in the past than guano. This has been due to the fact that the practice of selling guano on analysis—especially among retail buyers—did not largely obtain in the early years of the trade. A good deal of this adulteration was probably caused by ignorant prejudice on the part of the farmer, to whom the pungency of its smell and its colour were too apt to be ranked as its most important properties. The variation in the quality of different kinds of guano was too often not sufficiently realised by the buyer, who not unfrequently was made to pay as high a price for guano of an inferior quality as he ought to have paid for that of the best quality. Indeed no manure illustrates the importance of chemical analysis more than guano. Among the different forms of adulteration practised may be mentioned the addition of such substances as sawdust, rice-meal, chalk, sulphates of lime and magnesia, common salt, sand, earth, peat, ashes of various kinds, and water. There can be no doubt, however, that such adulteration has now long ceased to be practised to any extent. Nevertheless, it may be of use to draw attention to one or two of the tests by means of which some of the commoner forms of adulteration may be detected. One or two are extremely easily detected—as, for example, adulteration with sand or other mineral substances. In such a case, the percentage of ash left on burning a small portion of the guano will be found to be excessive. The percentage of ash in a sample of genuine Peruvian guano should not exceed from 50 to 60 per cent. The colour of the ash is another important point, and may serve as a further indication of adulteration. In the case of genuine guano, this should be whitish or greyish. Red-coloured ash generally points to the adulteration of the guano with some mineral substance containing iron—such, e.g., as Redonda phosphate, a mineral phosphate of iron and alumina. Where the ash is white, but excessive in quantity, adulteration with common salt, sulphate of magnesia, gypsum, or chalk, may be suspected. The last-named substance is easily detected by treating it with any of the common acids, when brisk effervescence, due to the liberation of the carbonic acid, will ensue.[198] A further point of importance with regard to the ash is its solubility in water and in acids. A large insoluble residue may be taken as indicating adulteration with sand. Adulteration with water is also easily detected by heating a sample to the boiling temperature and determining the loss it sustains. Of course the amount of water varies in different samples. The appearance of the guano will serve fairly well to detect whether it is abnormally moist. It may be added, in conclusion, that Peruvian guano is extremely light; and while this by itself is not a sufficient test of genuineness, it may serve to confirm other tests.
III.—So-called Guanos.
Before concluding this chapter, reference may be made to certain manures which are commonly known under the name of guanos—such as "fish-guano," "flesh-guano," "meat-meal-guano," and "bat-guano,"—as well as to manures which may more conveniently be described here—viz., "fowl and pigeon dung."
Fish-Guano.
The application of fish, not suited for other purposes, to the fields as a manure is a practice which has obtained in certain parts of the country for a number of years. In many districts on the sea-coast, where fishing is the chief industry, the only way in the past of disposing of a superabundant catch of herrings, for example, has been to utilise them as a manure. From such a practice has sprung up what is now an important and ever-increasing trade—viz., the manufacture of fish-guano.
This manufacture was first started, and is still most largely practised, in Norway. The guano obtained varies very considerably in quality according to the nature of the process employed, and as to whether the guano is made from whole fish or merely from fish-offal. The latter source is the common one. The manufacture is carried on at the fish-curing stations, and the quality of the guano made from this source is somewhat different from that made from whole fish, as a large proportion of the fish-offal is made up of bones and heads. Large quantities of Norwegian fish-guano are exported to various parts of Europe.
The best quality of this guano may contain as much as 10 per cent of nitrogen, but as a rule it is nearer 8 per cent. A very considerable variation in the amount of phosphoric acid occurs for the reason above stated, the guano made from fish-scrap being naturally much richer in this ingredient than whole-fish guano. The phosphoric acid may be said to range from 4 to 15 per cent, and there is also a small quantity of potash present.
Guano is also manufactured in Norway from the carcasses of whales. Such guano contains from 7-1/2 to 8-1/2 per cent of nitrogen, and about 13-1/2 per cent of phosphoric acid.
In America fish-guano is manufactured to a considerable extent—one important source being the menhaddo, a coarse sort of herring. This fish is caught for the sake of its oil, which is extracted by boiling, the residue being manufactured, after pressing and drying, into guano.
In this country the manufacture of fish-guano is carried out to a considerable and increasing extent. Formerly it was imported from Norway to a larger extent than is now the case, the present annual imports amounting only to 1000 or 2000 tons. The total annual production in the United Kingdom is probably 7000 or 8000 tons.
Value of "Fish-Guano."
That fish-guano is a valuable manure there can be no doubt. What, however, impairs its value is the fact that, as a rule, it contains a certain amount of oil. The effect of this oil is to retard fermentation and decomposition when the guano is applied to the soil, and thus render its action slower than would otherwise be the case.
When applied to the soil, therefore, every opportunity ought to be given to promote its fermentation. It is best applied some time before it is likely to be used. It ought to be well mixed with the soil-particles, and not allowed to lie on the top of the soil. Its best effect will be on light well-cultivated soils, which permit of the access both of sufficient moisture and of sufficient air for rapid fermentation. Its value as a manure for hops, vines, grass, and strawberries has been found to be considerable. It has been recommended to be applied along with farmyard manure; and such a mode of application is no doubt well suited to promote its decomposition. It has also been used for mixing with superphosphate of lime. Professor Storer has advocated a more general use of fish as a manure than is at present the case. He suggests that even fish not suitable for edible purposes might be caught for the purpose of conversion into manure. The difficulty of preserving fish, however, is considerable; and he suggests the use of potash salts, such as muriate of potash, or lime for this purpose. The benefit of using potash would be twofold. In addition to acting as a preservative, it would considerably enhance the value of the resulting guano as a manure. There is much truth in Professor Storer's views; and no doubt, as our sources of artificial nitrogenous manures grow more limited, the manufacture of fish-guano will be carried on in the future on a larger and more systematic scale than hitherto.
What is called "meat-meal guano" is generally that made from the refuse of the carcasses of cattle after they have been treated for their meat-extract according to Liebig's process. The meat-meal is used both for feeding and manurial purposes. Considerable quantities[199] of this guano are imported annually into this country from South America, Queensland, and New Zealand,—that coming from Frey Bentos, in Uruguay, being best known. It is a valuable manure, especially so for its nitrogen, which varies from 4 to 8 per cent, while it contains of phosphoric acid from 13 to 20 per cent. Some meat-meal guanos contain as much nitrogen as 11 per cent.
In some parts of the world, more especially in Germany, the carcasses of horses, as well as cattle, dogs, pigs, &c., which have died of disease, are converted into a guano. They are subjected to treatment by steam in digestors, by which means the fat and gelatine are separated and utilised, while the remaining portion of the animal is converted into guano. Other processes are also employed. The resulting manure contains from 6 to 10 per cent of nitrogen, and from 6 to 14 per cent of phosphoric acid.
Value of Meat-meal Guano.
Meat-meal guano is a valuable nitrogenous manure. The same remarks apply to it as to fish-guano, although it ferments probably very much more quickly than the latter, and is undoubtedly a more valuable manure.
Bat Guano.
In conclusion, we may consider bat guano. Bat guano, which is really a very rare curiosity, has been found accumulated in hot climates in caves.
The samples which have been analysed have differed very much in quality, some containing as much as 9 per cent of nitrogen and 25 per cent of phosphoric acid. Provided it could be obtained in any quantity, and of a quality even approximating to the above analysis, it need scarcely be pointed out that bat guano would be a most valuable manure.
A singular point about its composition is, that it has been found to contain a considerable proportion of its nitrogen (as much as 3 per cent) in the form of nitrates.
Pigeon and Fowl Dung.
Pigeon dung is a manure which historically is of great importance. The dung of pigeons was used as a manure by the ancient Romans; and even in modern times, more especially in France, it was considered a most important fertiliser. Despite these facts, pigeon dung is by no means a rich manure, and its composition compares most unfavourably with that of the guanos we have just been considering. According to Storer,[200] it only contains from 1-1/4 to 2-1/2 per cent of nitrogen, and from 1-1/2 to 2 per cent of phosphoric acid, and a little over 1 per cent of potash.
The dung of poultry is just about as poor, fowl dung containing from .8 to 2 per cent of nitrogen, 1-1/2 to 2 per cent of phosphoric acid, and a little under 1 per cent of potash; while that of ducks and geese is even poorer.[201]
From these statements it will be seen that the excrements of pigeons, hens, and ducks do not form a rich manure. One thing about pigeon dung which is to be noticed, is the fact that it ferments very quickly.
None of the pseudo-guanos, however rich they may be in manurial ingredients, can be regarded as equal in their action to the genuine article, for reasons which we have gone into already when considering the action of guano.
FOOTNOTES:
[183] Bones, it is true, were in use long before guano; but popular as they deservedly were, they had not been used, at the time of the importation of guano, to any very considerable extent.
[184] The total annual imports at present may be taken at under 30,000 tons, whereas in 1855 they amounted to over 200,000 tons. For statistics on this point the reader is referred to the Appendix, Note I., p. 327.
[185] With regard to the origin of certain guano deposits, which are of very recent date—e.g., Angamos and Ichaboe—there can be no doubt whatever, because we can witness the process of formation still taking place. It is not so, however, with regard to older deposits, for which some have been inclined to claim mineral origin. The best proof that such deposits owe their origin mainly to bird excrements is the comparatively large quantity of uric acid they contain. On the other hand, the evidence in support of the belief that they are also formed from the remains of the birds themselves and other animals, is to be found in the large proportion of phosphates they contain, and the presence in the deposits of feathers and the fossilised skeletons of the animals above mentioned.
[186] A complete list of the various deposits will be found in the Appendix, Note II., p. 327. It may be noticed that nearly all the deposits lie within 10° to 20° north and south of the Equator.
[187] See Chapter on Farmyard Manure, p. 257.
[188] According to Nesbit, some of the cargoes of this guano contained hard saline lumps of very little manurial value—over 50 per cent being common salt.
[189] The salt exports were made in 1868.
[190] For analyses of these nodules and crystals, see Appendix, Note III., p. 328.
[191] See Heiden, vol. ii. p. 356.
[192] See Appendix, Note IV., p. 329.
[193] The Ichaboe guano at present exported is a fresh deposit, and is annually collected for shipment.
[194] Further chemical changes have occurred in certain cases between the guano and the limestone rock beneath, resulting in the formation of what is called a "crust" guano. Such guanos form a soft phosphatic rock, and are extremely rich in phosphates. As examples of these "crust" guanos may be mentioned Sombrero, Curaçao, Aruba, Mexico, and Navassa phosphates.
[195] The presence in the old Peruvian guano of concretionary nodules has already been referred to.
[196] According to Vogel the nitrogen as urates is converted by the sulphuric acid into ammonia salts.
[197] See Appendix, Note VI. p. 330.
[198] It must be remembered, however, that even genuine guano contains a certain quantity of carbonate of lime, and will give a slight amount of effervescence when so treated.
[199] The annual imports may be stated at from 3000 to 4000 tons.
[200] Agricultural Chemistry, vol. i. p. 367.
[201] See Appendix, Note VII., p. 331.
APPENDIX TO CHAPTER VIII.
NOTE I. (p. 297).
Peruvian Guano Imported into the United Kingdom, 1865-1893.
| Year. | Tons. |
| 1865 | 213,024 |
| 1870 | 247,028 |
| 1871 | 144,735 |
| 1872 | 74,964 |
| 1873 | 135,895 |
| 1874 | 94,346 |
| 1875 | 86,042 |
| 1876 | 158,674 |
| 1877 | 111,835 |
| 1878 | 127,813 |
| 1879 | 45,475 |
| 1880 | 58,631 |
| 1881 | 33,393 |
| 1882 | 27,382 |
| 1883 | 36,713 |
| 1884 | 15,802 |
| 1885 | — |
| 1886 | 28,733 |
| 1887 | 5,784 |
| 1888 | 16,446 |
| 1889 | 17,000 |
| 1890 | 19,000 |
| 1891 | 11,000 |
| 1892 | 14,000 |
NOTE II. (p. 298).
Guano Deposits of the World.
NOTE III. (p. 303).
Composition of Concretionary Nodules.
(Analyses by Karmrodt.)
| No. 1 | |
| Potassium sulphate | 7.49 |
| Potassium phosphate | 9.52 |
| Sodium phosphate | 9.08 |
| Ammonium phosphate | 7.57 |
| Calcium sulphate | 3.40 |
| Ammonium urate | 4.09 |
| Ammonium oxalate | 41.28 |
| Nitrogenous organic matter | 10.17 |
| Water | 7.40 |
| 100.00 | |
| Nitrogen - 14.84 | |
| No. 2 | |
| Potassium sulphate | 45.64 |
| Sodium sulphate | 13.22 |
| Ammonium sulphate | 10.23 |
| Ammonium oxalate | 9.14 |
| Basic ammonium phosphate | 12.09 |
| Precipitated ammonium phosphate | 4.78 |
| Organic matter | .94 |
| Insoluble | 1.90 |
| Water | 2.06 |
| 100.00 | |
The following analyses, being the average of a large number of different samples analysed from time to time in the chemical laboratory of the Pommritz Agricultural Experimental Station, show the gradual deterioration of Peruvian guano, as regards its percentage of nitrogen, during the years 1867-81:—
| Nitrogen. | |
| 1867 | 13.16 |
| 1868 | 11.98 |
| 1869 | 13.66 |
| 1870 | 12.37 |
| 1871 | 10.04 |
| 1872 | 10.72 |
| 1873 | 9.16 |
| 1874 | 9.83 |
| 1878 | 7.10 |
| 1879 | 6.95 |
| 1880 | 7.07 |
| 1881 | 6.93 |
NOTE V. (p. 309).
Composition of Different Guanos.
The following is a list of the more common nitrogenous and phosphatic guanos which have been used in the past or are at present in use. Those printed in italics are still being worked. As their value depends on their nitrogen and phosphoric acid, these alone have been given. The percentages must be taken as mere approximations, as the quality of different cargoes from the same deposits varies very much. The table may be found useful for reference.
Nitrogenous Guanos.
Phosphatic Guanos.
| Phosphoric | } { | Tricalcic | |
| acid | } = { | phosphate. | |
| per cent. | per cent. | ||
| Maracaïbo, or Monks | 42 | 92 | |
| Raza Island | 40 | 87 | |
| Curaçao | 40 | 87 | |
| Baker Island | 39 | 85 | |
| Starbuck | 38 | 83 | |
| Enderbury | 37 | 81 | |
| Californian | 35 | 76 | |
| Aves | 34 | 74 | |
| Fanning Island | 34 | 74 | |
| Howland | 34 | 74 | |
| Sidney Island | 34 | 74 | |
| Mejillones | 33 | 72 | |
| Lacepede Island | 33 | 72 | |
| Malden Island | 32 | 70 | |
| Sombrero | 32 | 70 | |
| Browse Island | 31 | 68 | |
| Huon Island | 28 | 61 | |
| Patos Island | 24 | 52 | |
| Jarvis Island | 20 | 44 | |
| Cape Vert | 11 | 24 |
NOTE VI. (p. 314).
It may be of interest to refer to a theory put forward by Liebig as to the action of oxalic acid in guano. This, he considered, had the effect of gradually rendering the insoluble calcium phosphate soluble, and giving rise to the formation of ammonium phosphate and calcium oxalate. Such an action would probably take place were the guano allowed to ferment by itself. We know, however, that when it is brought in contact with the soil-particles, all its soluble phosphate is converted into precipitated phosphate.