Manures and the principles of manuring

Potatoes grown with Uncovered Manure.

Potatoes grown with Covered Manure.

This shows an increase of about 4 tons of potatoes per acre with the covered manure.

"The next year the weather was wet, grain soft and not in very good order, but the following was the amount of produce:—

Wheat grown with Uncovered Manure.

Wheat grown with Covered Manure.

NOTE XV. (pp. 231, 264).

Drainings of Manure-heaps.

The importance of not separating the liquid portion from the solid portion has already been pointed out in dealing with the composition of the solid excreta and the urine. These two constituents of the manure are complementary to one another, and the value of farmyard manure as a general manure is very much impaired if the liquid portion is not applied along with the solid. In one important respect do the drainings of manure-heaps differ from urine—that is, in the percentage of phosphates they contain, the latter being practically devoid of phosphoric acid.

The following is an analysis of drainings from a manure-heap (Wolff):—

NOTE XVI. (p. 270).

Amounts of Potash and Phosphoric Acid removed by the following Rotations from a Prussian Morgen (.631 Acre).

NOTE XVII. (pp. 253, 254).

Composition of Farmyard Manure (Fresh), (calculated by Sir John Lawes).

NOTE XVIII. (p. 232).

The Urine.

An important consideration we have omitted to take note of in the text is the quantity of the urine voided. It is this consideration that renders the urine so much more valuable than the solid excreta. In the case of a man it has been estimated that the urine voided is fifteen times as much, is twelve times as rich in nitrogen, three times in potash, and two in phosphoric acid, as the solid excreta (Munro). The relation of solid matter in the case of the farm animals is not exactly similar. The urine of the ox is about twice the weight of its solid excreta. Both the horse and the sheep, however, void as a rule more solid excreta than urine. Munro, in his work on 'Soils and Manures,' contrasts the composition of the urine and solid excreta of the different farm animals by the following statement:—

FOOTNOTES:

CHAPTER VIII.

GUANO.

Importance in Agriculture.

In the consideration of artificial manures, guano deserves the first place. This it does mainly on historical grounds, as it is now largely a manure of the past. Not merely has it been used in agriculture to an extent to which no other artificial manure has as yet ever approximated, but its influence on agricultural practice has been enormous. Introduced into this country about the middle of the present century, it was the first of artificial manures to be used in large quantities.[183] It may be thus described as having introduced the modern system of intensive cultivation, and given rise to the now almost universal practice of artificial manuring.

Influence on British Farming.

It is, indeed, difficult to over-estimate the important influence which the introduction of this most valuable fertiliser has exercised on British as well as, to a large extent, on European husbandry. Before its introduction the farmer was almost completely dependent on his farmyard manure. He was tied down to a great extent, by the exigencies of the then prevailing agricultural customs, to certain rotations of crops. He could do little in the way of enriching barren soils or of ensuring a heavy yield of crop. By the use of this very potent fertiliser, he quickly discovered that the most wonderful results ensued—results which must have seemed to him at first little short of miraculous. He found that by the application of a few hundredweights per acre, poor soils could be made to yield large returns, and that barren patches in a field could be brought up to the average of the surrounding portions by sprinkling merely a few handfuls of it; that by its means a good start could be ensured to every crop, and one slow of coming away could be hastened on. In short, in this wonderful brown powder, with such a characteristic odour, the astonished farmer discovered a manure which, for the speed of its action, and for the increase of crop it gave, completely threw into the shade both farmyard manure and bones. What wonder, then, that its fame as a manure should have become so quickly known and its use so extensive! It thus gave a most powerful impetus to intelligent farming by bringing home to the minds of those who used it the important position nitrogen and phosphates occupied as constituents of the soil, and the influence they exercised on plant-growth. It furnished, in fact, on an enormously large scale, a practical demonstration of the principles of manuring. The educational value which the use of guano thus exercised may be said to have been very great. It also led the way to the use of the various artificial manures so much used during the last fifty years. Impressed by the value of guano, farmers were favourably disposed towards the use of other fertilisers; and, largely owing to its widespread popularity, the new practice speedily gained ground.

Influence not wholly for Good.

But its influence, it must be admitted, was not wholly for good. In its very popularity lay the danger of its abuse. Had its value and the method of its action been more widely understood, and had the principles upon which the practice of artificial manuring depends been better realised, agriculturists would have been spared much of the needless pecuniary losses they sustained by being imposed upon by unscrupulous manure-dealers. Among the farming community the word guano soon became a name to conjure with, and under this title many spurious and worthless manures were attempted to be palmed off on the unwary farmer. Even the genuine article, there can be little doubt, was at one time largely adulterated; and as the farmer was almost invariably content to purchase the article not on any guaranteed chemical analysis, but simply on the ground of its appearance, colour, and more especially smell, every facility was given for the successful perpetration of such fraudulent imposition. Guano, it was very soon found, varied in its composition, but this variation in quality the farmer did not recognise. In the early days of its use all guano was in his eyes of the same value. Too often, as we have just pointed out, provided it had a good colour and a strong odour, it was all right. Under such conditions, it can scarcely be wondered at that its introduction should have proved not an unmixed blessing to agriculture.

Its Value as a Manure.

Guano derives its value as a manure from the nitrogen, phosphates, and the small amount of potash it contains. This at any rate is true of the great bulk of guano which has been used in the past. There are, as we shall immediately see, certain kinds of guano, known as phosphatic guanos, which only contain phosphates. The amount of such purely phosphatic guano directly used as a manure in this country is, however, inconsiderable, and guano may truly be described as owing its value chiefly to its nitrogen. Not a little of its value and popularity as a manure may be said to be due to the fact that it contains all of the three important manurial constituents, and that in this respect it may be regarded in a sense as a general manure, thus resembling most nearly, of all artificial manures, farmyard manure. Although its sources are now, to a very large extent, exhausted, and its total annual imports into this country are at present considerably less than what they were thirty or forty years ago,[184] it may be well, on account of its historical importance, to give a somewhat detailed account of its origin, occurrence, and value as a manure.

Origin and Occurrence.

Guano (which means dung)—or huano, as it is spelt in the Spanish language—was first used in Peru. It seems to have been used there long before that country was discovered by the Spaniards—probably as early as the twelfth century. Regarding its origin there can be little doubt. It is almost entirely derived from the excrements of sea-birds, such as pelicans, penguins, and gulls, as well as from the remains of the birds themselves, and of seals, walruses, and various other animals.[185] Under the influence of a tropical sun, and in a region in which rain scarcely ever falls, these excrements are soon dried, and remain little changed in their composition through centuries. Many of the Peruvian deposits must be extremely old, as they are covered up with sand and other débris, and are of considerable depth. Especially is this the case with deposits occurring on the mainland, such as those at Pabellon de Pica, where the layer of sand or conglomerate covering up the deposit varies in depth from a few feet to over a hundred. The effect of this superficial covering has been to protect the guano, to a certain extent, from loss of nitrogen.

Although guano of the best class has been derived from the neighbourhood of Peru, deposits have also been found in many other parts of the world—viz., in North America, West Indies, Australia, Asia, Africa, and among the islands of the Pacific.[186]

Variation in the Composition of different Guanos.

The guano found in these different deposits varies very considerably in composition. This is due to the difference in the nature of the prevailing climate of the places where these deposits occur. Where the climate is dry and warm, as is the case in Chili and Peru, the excrements dry quickly and remain very little changed, as one very important condition of fermentation—viz., moisture—is absent.[187] In a damp climate, on the other hand, speedy fermentation ensues, resulting in the loss of nearly all the organic matter, including nitrogen, in such volatile forms as carbonate of ammonia, carbonic acid gas, water, &c. The soluble alkalies, the most important of which is potash, as well as the soluble phosphates, are also, under such conditions, lost to the guano by being washed out by the rain. We have thus a wide difference in the quality of the different deposits, depending on the extent to which decomposition has taken place. Guano thus ranges from the rich nitrogenous Peruvian kind, which has undergone little or no change from the time of its deposit, to the purely phosphatic kind (such as those of Malden and Baker islands), in which everything of manurial value has been lost except the insoluble phosphate of lime. Even among the nitrogenous guanos we find a considerable difference in quality, some deposits being partially impoverished by the action of the atmospheric moisture, dew, spray or sea-water, but still containing a considerable proportion of their nitrogen. Other deposits, again, are largely admixed with sand, which has been blown in upon them to such an extent as to make them unsaleable. We can divide guano, therefore, into two great classes—viz., nitrogenous and phosphatic.

I.—Nitrogenous Guanos.

(a) Peruvian.

By far the most valuable and abundant deposits as yet discovered have been those on the Peruvian and Chilian coasts. As already pointed out, guano seems to have been used in this country from a very early period; and so impressed were the Incas with its importance as a manure, that the penalty of death was imposed on any one guilty of killing the sea-fowl during the breeding season in the vicinity of the deposits.

The occurrence of guano in Peru seems first to have been made known in Europe in the beginning of the eighteenth century. It was not, however, till the beginning of the present century—viz., 1804—that A. Humboldt, the great German traveller, brought some of the wonderful fertiliser home with him, and that its composition was able to be investigated by chemical analysis. Shortly afterwards, its practical value was demonstrated by experiments carried out on potatoes by General Beatson in St Helena. To Lord Derby is due the credit of having first introduced it into this country, the earliest importation into Liverpool being in 1840. Experiments were shortly afterwards instituted in different parts of the country, prominent among which were those by Sir John Lawes and Sir James Caird; and so striking were the results obtained, that the manure rapidly found favour with the farming community—so much so, that ten years later the importations into this country amounted to no less than 200,000 tons, while in 1855 the total exports from the west coast of South America reached the enormous amount of 400,000 tons. In all, it has been estimated that since the year 1840 over 5,000,000 tons of Peruvian guano have been imported into this country.

Different Deposits.

Peruvian guano has been derived from various deposits occurring in different parts of the coast, and from a number of small adjacent islands. The richest of these was that found on Angamos, a rocky promontory on the coast of Bolivia. Samples of this guano contained as high as 20 per cent of nitrogen (equal to 24 per cent ammonia).[188] Unfortunately, however, the quantity of this deposit was extremely limited, and became rapidly exhausted. Next to this deposit in quality was the guano found on the Chincha islands, three little islands off the coast of Peru. These deposits were the largest which have ever been discovered, and for a period of nearly thirty years were almost the sole source of the Peruvian guano sold in commerce, over 10,000,000 tons having been exported from them alone. Some of this guano contained 14 per cent of nitrogen (equal to 17 per cent ammonia); and although part of the guano shipped from these islands was not quite so rich, yet it was all of a high-class order. The deposits on these islands were in many cases 100 to 200 feet in depth, and rested on rocks of granite. The lower layers were consequently found to be poorer in quality, and mixed with pieces of granite. The Chincha island deposits have been long exhausted,[189] and the chief deposits of Peruvian guano since worked have been those on Guanape and Macabi islands—a considerably inferior guano, containing only 9 to 11 per cent of nitrogen (equal to 11 to 13 per cent of ammonia)—which in their turn have become exhausted; from Ballestas, almost as rich as the Chincha island guano, also now exhausted; and from Pabellon de Pica, Punta de Lobos, Huanillos, Independence Bay, and Lobos de Afuera. Quite recently a deposit of very high-class guano was discovered in Corcovado, and a good many cargoes have already been shipped to this country. It is found to contain nitrogen equal to from 10 to 13 per cent ammonia, 30 to 35 per cent phosphates, and some potash, being thus a most valuable guano.

Appearance, Colour, and Nature.

In colour it varies from a very light to a very dark brown, the richer samples being generally lighter. Samples taken from even the same deposit have been found to differ very considerably in appearance, those taken from the lower and older layers being usually darker than those taken from the more recent upper layers. It was soon found also to vary very much in composition. After a deposit had been worked for some time, the quality of guano it yielded was found to be inferior and coarser, and in many cases mixed with pebbles or pieces of granite, porphyry, &c. This led to the custom of screening it on arrival in this country, before it was used as a manure. In the richer qualities—e.g., in the Chincha guano—little round concretionary nodules, varying in colour from pure white to dark brown, were occasionally found. Analysis showed these nodules[190] to be composed chiefly of potash salts. Sometimes, also, little crystals of almost pure ammonia salts were found. It soon became customary, therefore, to prepare guano for the market by separating the stones and reducing the whole to a fine uniform powder. One of its most characteristic properties, and the one which seems to have impressed the public most, was its pungent odour. Undue importance was attached to this property, in the belief that it was caused by the ammonia it contained. It may be doubted, however, whether the characteristic smell of guano is due so much to its ammonia as to certain fatty acids.

Composition.

In composition it is of a most complex nature. It contains its nitrogen in a great variety of forms, the chief of these being urate, oxalate, ulmate, humate, sulphate, phosphate, carbonate, and muriate of ammonia; and also in a rare form of organic nitrogen peculiar to guano, called guanine. According to Boussingault, some guanos contain small quantities of nitrates. Its phosphoric acid is present both in the soluble state—viz., as phosphates of the alkalies (ammonia and potash)—and in the insoluble state as phosphate of lime; and lastly, its potash is present as sulphate and phosphate. The proportion in which these different forms of nitrogen and phosphoric acid are present varies considerably in different samples. The richer a sample, as a rule, the more nitrogen in the form of uric acid it contains. The most of the nitrogen is present as uric acid and ammonia. Damp guanos contain more of their nitrogen as ammonia than dry ones, this being due to the fermentation which goes on in the former. On an average, about a third of its total nitrogen is soluble in water. Of its phosphates, on the other hand, only about a fourth are soluble in water.

The following analyses of a sample of Chincha island guano by Karmrodt[191] will illustrate this. (Sample dried at 212° Fahr.):—

1. Constituents easily soluble in Water.

2. Difficultly soluble in Water, soluble in Acids, Alcohol, and Ether.

In the above analysis it will be noticed that none of the ammonia is present as carbonate. In most samples, however, of Peruvian guano, the ammonia in this form amounted to from 1 to 2 per cent. In the inferior qualities, chiefly those which had been subjected to the action of water, and consequently of fermentation, to a certain extent, this form of ammonia was found to be most abundant. Such guanos were most liable to loss of nitrogen by volatilisation.

The older Peruvian guano contained as high as 14 per cent of nitrogen (equal to 17 per cent of ammonia), and of phosphoric acid 12 to 14 per cent (equal to 26 to 28 per cent of phosphate of lime). It, however, gradually deteriorated in quality as the deposits became worked out, the percentage of nitrogen becoming year by year less, until latterly Peruvian guano, as imported, contains only from 3 to 4 per cent of nitrogen (equal to 4 to 5 per cent of ammonia). This guano is, however, richer in phosphates, containing often 50 to 60 per cent of phosphate of lime, and 3 to 4 per cent of potash.[192]

(b) Other Nitrogenous Guanos.

The guanos, other than those which come from Peru, are chiefly purely phosphatic guanos, so that the term Peruvian has not unfrequently in the past been used as a generic term synonymous with the term nitrogenous, and consequently applied to all nitrogenous guanos independent of their source. There are, however, a few deposits other than the Peruvian which have yielded considerable quantities of valuable nitrogenous guano. Of those, the richest in quality—in fact, the richest of any deposits hitherto discovered—was the Angamos guano, which came from a rocky promontory on the coast of Bolivia. The few samples of this which have been analysed showed over 20 per cent of nitrogen. Unfortunately, the deposit proved to be comparatively insignificant in amount, and has long been exhausted.

Poorer in quality, but more abundant in quantity, were the deposits found on the Ichaboe and other islands off the south-west coast of Africa. These deposits were discovered shortly after the introduction of Peruvian guano, and for a few years supplied considerable quantities of valuable manure. The deposits first discovered were soon exhausted, so that for a number of years Ichaboe guano ceased to be procurable. Fresh deposits, however, were subsequently found, and considerable quantities have of late years been used in agriculture.[193] Ichaboe guano is inferior in value to Peruvian. It exemplifies the influence of small quantities of rain on guano deposits in impoverishing them in their nitrogen. In much of the Ichaboe guano imported into this country a large amount of feathers is found. It also contains an abnormally large quantity of insoluble matter.

Among the other nitrogenous guanos may be mentioned the Patagonian, Falkland, and Saldanha Bay. They are, like the Ichaboa, of comparatively recent origin, and are collected in small quantities after the breeding season every year.

II.—Phosphatic Guanos.

Phosphatic guanos, as already pointed out, are similar in origin to nitrogenous guanos. In their case, however, the nitrogen, alkalies, and soluble phosphates which they originally contained have been almost entirely lost by the decomposition of their organic matter and the action of water.[194] Most of them still contain very small quantities of nitrogen, amounting to a fraction of a per cent. Of these deposits there are very many occurring on islands in different parts of the world. In appearance the guano obtained from them is very different from nitrogenous guano, being much lighter in colour, and of a fine powdery nature. It forms a very rich phosphatic guano, containing in many cases between 70 and 80 per cent of insoluble phosphate of lime. Such guanos are largely used in the manufacture of high-class superphosphates, by treating them with sulphuric acid. Being of an insoluble nature, they are not very suitable for direct application to the soil. Of these phosphatic guanos the following are the chief—those marked in italics being still unexhausted:—

1. Baker, Jarvis, Howland, Starbuck, Flint, Enderbury, Malden, Lacepede, Browse, Huon, Chesterfield, Sydney, Phœnix, Arbrohlos, Shark's Bay, and Timor—all found on islands in the Pacific Ocean.

2. Mejillones, on the coast of Bolivia.

3. Aves, Tortola, Mona, and other deposits in the West Indies.

4. Kuria Muria islands, in the Arabian Gulf.

For further particulars as to the composition of these different guanos, the reader is referred to the Appendix, Note V., p. 329.

Inequality in Composition.

That guano was a substance of by no means uniform composition was a fact early recognised in the history of the trade. Not only did guano from different deposits show on analysis different percentages of the manurial ingredients, but different samples of guano from the same deposit were often found to differ very considerably from one another. It soon became the custom, therefore, to sell it on chemical analysis, each separate cargo being carefully analysed. But this custom did not wholly obviate the difficulty, as the guano in even one cargo might differ. In the case of the older and richer guanos, there was certainly more uniformity in quality, but they were liable to differ in their percentage of nitrogen.[195] As, however, the deposits became gradually worked out, their lower layers were found more or less largely admixed with stony and earthy matter, and their composition was naturally rendered very variable. This state of matters was unsatisfactory to buyers and sellers, and led to much friction between the two, as it was found wellnigh impossible on the part of the seller to guarantee the composition of his manure. The custom of preparing the material by reducing it to a fine powder before sending it into the market, and the custom, subsequently introduced, of treating it with sulphuric acid, have done away with this difficulty to a large extent.

"Dissolved" Guano.

The treatment of guano with sulphuric acid was first had recourse to in the case of cargoes damaged with water. In such guano, as has been already pointed out, fermentation has been permitted to take place, with the result of the formation of volatile carbonate of ammonia in greater or less quantity. By the addition of sulphuric acid the ammonia was fixed, and the guano was prevented from losing its most valuable constituent. It was soon found, however, that guano so treated possessed greater activity as a manure. The result of the sulphuric acid was to increase very materially the amount of its soluble phosphates, and also its soluble nitrogen compounds.[196] It had, moreover, the effect of producing a guano of uniform composition. The custom, first introduced in 1864 by Messrs Ohlendorff & Co., was soon largely practised. The guano is treated with 25 to 30 per cent sulphuric acid (sp. gr. 1.73). After a short time the resulting hard mass is, by means of disintegrators, reduced to a uniform powder.

"Equalised" or "Rectified" Guano.

As guano decreased in its quality the demand for a high-class article became more and more difficult to meet. This led to the custom of "fortifying" or "rectifying"—as it is variously called—the natural material with sulphate of ammonia. A manure closely resembling in the percentage of its manurial constituents the older rich guanos is thus obtained. Of these so-called "equalised" guanos, two qualities are at present sold, the first being guaranteed to contain nitrogen equal to 8 to 9 per cent ammonia, 30 to 35 per cent phosphates, and 2 to 3 per cent of potash; the second quality containing only about half as much nitrogen, but more phosphates.

However valuable this fortified guano may be—and it is, undoubtedly, a most valuable manure—its action cannot be supposed to be exactly similar to the old Peruvian guano, which it resembles in the percentage of its nitrogen, phosphates, and potash. Much of the distinctive value of guano as a manure, as will be pointed out immediately, lies in the fact that it contains its manurial ingredients in a variety of differently soluble compounds, which are gradually rendered available in the soil for the plant's needs. This undoubtedly is one of the reasons why the action of guano among manures is quite unique; and there are other reasons which we probably do not clearly understand. However skilfully the composition of the guano may be artificially simulated, it still remains an undoubted fact that the "equalised" guano is not exactly similar in its action to the genuine article. Nevertheless, that it is superior in its results to the poorer classes of guano at present available, and to ordinary compound manures, there can be little doubt. A great merit of the equalised guano is, however, that it is sold at a lower price than guano as imported; and as the guano is sold on a guaranteed analysis, the practice has done much to advance the true interests of agriculture.