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Manures and the principles of manuring
by Charles Morton Aikman
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As has already been pointed out, the excrements of the pig are, as a rule, very poor in nitrogen. This accounts for the fact that pig-manure is a "cold" manure, slow in fermenting.[160]

4. Sheep-manure.

The dung and the urine of the sheep, as we have already seen, are, weight for weight, the most valuable of any of the common farm animals. The total weight of the excrements voided by a sheep in a day may be taken, on an average,[161] at 3.78 lb., of which .97 lb. is dry matter. These excrements contain .038 lb. of nitrogen and .223 lb. mineral matter. Taking the amount of straw most suitable for absorbing this quantity of excrementitious matter at three-fifths of a pound, then the manure produced by a sheep in a day will contain .0429 lb. nitrogen and .264 lb. mineral matter. That is, in a year the quantities of nitrogen and mineral matter in the manure produced by a sheep would be 15.66 lb. of nitrogen and 96.36 lb. of mineral matter.

From its richness in nitrogen, and from its dry condition, sheep-dung is peculiarly liable to ferment. While richer in fertilising substances than horse-manure, it is not so rapid in its fermentation. This is due to the harder and more compact physical character of the solid excreta. The risks of loss of volatile ammonia are, in its case, exceptionally great. The use of artificial "fixers" is therefore to be strongly recommended.[162]

Fermentation of Farmyard Manure.

Having now considered the nature of the different manures produced by the four common farm animals separately, it is of importance to consider the exact nature of the fermentation, decomposition, or putrefaction which takes place in the manure-heap.

It is now more than thirty years since Pasteur showed that the fermentation which ensued on keeping a sample of urine was due to the action of a minute organism, for the propagation of which a certain amount of warmth, air, and moisture, as well as the presence of certain food-constituents, especially nitrogenous bodies, were necessary.

Subsequent researches by Pasteur and others have conclusively demonstrated that the micro-organic life instrumental in effecting the putrefaction or decay of organic matter of any kind, may be divided into two great classes:—

1. Those which require a plentiful supply of oxygen for their development, and which, when bereft of oxygen, die—known as aerobies.

2. Those which, on the contrary, develop in the complete absence of oxygen, and which, when exposed to oxygen, die—known as anaerobies.

In the fermentation of the manure-heap, therefore, we must conceive of the two classes of organisms as the active agents. In the interior portion of the manure-heap, where the supply of oxygen is necessarily limited, the fermentation going on there is effected by means of the anaerobic organism—i.e., the organism which does not require oxygen; while on the surface portion, which is exposed to the air, the aerobic (or oxygen-requiring) organism is similarly active. Gradually, as decay progresses, the aerobic organisms increase in number. It is through their instrumentality that the final products of decomposition are largely produced. The functions of the anaerobic organisms may be, on the contrary, regarded as largely preparatory in their nature. By breaking up the complex organic substances in the manure into new and simpler forms, they advance the process of putrefaction through the initial stages; and when this is accomplished, they die and give place to the aerobic, which, as we have just seen, effect the final transformation of the organic matter into such simple substances as water and carbonic acid gas.

The conditions influencing the fermentation of farmyard manure may be summed up as follows:[163]—

1. Temperature.—The higher the temperature the more rapidly will the manure decay.

2. Openness to the Air.—Of course it will be seen that the effect of exposing the manure to the action of the air is to induce the development of the aerobic type of organism, and thus to promote more rapid fermentation. If, on the other hand, the manure be impacted, the slower but more regular fermentation, due to the anaerobic type of organism, will be chiefly promoted. It must be remembered that in the proper rotting of farmyard manure both kinds of fermentation should be fostered. It is, in fact, on the careful regulation of the two classes of fermentation that the successful rotting of the manure depends. It must further be remembered that, even with a certain amount of openness in a manure-heap, anaerobic fermentation may take place. This is due to the fact that the evolution of carbonic acid gas, in such a case, is so great as to exclude the access of the atmospheric oxygen into the pores of the heap.

3. The dampness of the manure-heap is another important influence. This, of course, will act in two ways. First, by lowering the temperature. Where the manure-heap is found to be suffering from "fire-fang," the common method in practice is to lower the temperature by moistening the heap with water. Secondly, it acts as a retarder of fermentation by limiting the supply of atmospheric oxygen, and thus preventing, as we have just seen, aerobic fermentation.

4. The fourth chief influence in regulating fermentation of the manure-heap is its composition, and more especially the amount of nitrogen it contains in a soluble form. The rate at which fermentation takes place in any organic substance may be said chiefly to depend on the percentage of soluble nitrogenous matter it contains: the greater this is in amount, the more quickly does fermentation go on. There are always a number of soluble nitrogenous bodies in farmyard manure. These are chiefly found in the urine, such as urea, uric and hippuric acids, and ammonia salts.

Products of Decomposition of Farmyard Manure.

The most important of the changes which take place in the rotting of farmyard manure may be briefly enumerated as follows:—

1. The gradual conversion into gases of a large portion of the organic elements in the manure. Of these gaseous products the most abundant is _carbonic acid gas_ (CO_2). It is in this form that the carbonaceous matter which constitutes the chief portion of the manure escapes into the air. Carbon also escapes into the air, combined with hydrogen, in the form of _carburetted hydrogen_ or _marsh-gas_ (CH_4), a product of the decomposition of organic matter in the presence of a large quantity of water. This gas is consequently found bubbling up through stagnant water. Next to carbonic acid gas, _water_ (H_2O) is the most abundant gaseous product of decomposition. The nitrogen present in the manure, in different forms, is converted by the process of decomposition chiefly into _ammonia_, which, combining with the carbonic acid, forms carbonate of ammonia, a very volatile salt. It is to this fact that one of the great sources of loss in the decomposition of farmyard manure is due. If the temperature of the manure-heap be permitted to rise too high, the carbonate of ammonia volatilises. It is probable, also, that a not inconsiderable portion of the nitrogen escapes into the air in the free state. The last of the most important gaseous products of decomposition are _sulphuretted_ and _phosphoretted hydrogen_. It is to these gases that much of the smell of rotting farmyard manure is due.

2. The second class of substances formed are soluble organic acids, such as humic and ulmic acids. The function performed by these acids is a very important one. They unite with the ammonia and the alkali substances in the mineral portion of the manure, forming humates and ulmates of ammonia, potash, &c. It is these ulmates that form the black liquor which oozes out from the manure-heap.

In very rotten farmyard manure traces of nitric acid may be found; but it must be remembered that the formation of nitrates is practically impossible under the ordinary conditions of active fermentation of farmyard manure, except perhaps in its very last stages.

3. The third class of changes taking place have to do with the mineral portion of the manure. The result of the formation of so much carbonic and other organic acids is to increase the amount of soluble mineral matter very considerably.

Analyses of Farmyard Manure.

It is chiefly to the valuable researches of the late Dr Augustus Voelcker that we owe our knowledge of the composition of old and fresh farmyard manure. All interested in this important question should peruse the original papers on this subject contributed to the 'Journal of the Royal Agricultural Society' by Dr Voelcker. Typical analyses illustrating the variation in the composition of farmyard manure at different stages of decomposition will be found in the Appendix.[164] From what has been already said, it is obvious chat the composition of farmyard manure is of a very variable nature.

The quantity of moisture naturally varies most, and this variation will depend on the age of the manure, and the conditions under which it is permitted to decay. It may be taken at from a minimum of 65 per cent in fresh to 80 per cent in well-rotted manure. The total organic matter may be taken at from 13 to 14 per cent, containing nitrogen .4 to .65 per cent. The total mineral matter will range from about 4 to 6.5 per cent, containing of potash from .4 to .7 per cent, and of phosphoric acid from .2 to .4 per cent.[165]

As Mr Warington[166] has pointed out, one ton of farmyard manure would thus contain 9 to 15 lb. of nitrogen, about the same quantity of potash, and 4 to 9 lb. of phosphoric acid. These quantities of nitrogen and phosphoric acid, calculated to (95 per cent) nitrate of soda, and (97 per cent) sulphate of ammonia, and (25 per cent) superphosphate, give respectively 57.25 to 96 lb. nitrate of soda, 45 to 75 lb. sulphate of ammonia, and 35 to 79 lb. superphosphate. That is, in order to apply as much nitrogen to the soil as is contained in one ton of nitrate of soda, we should require to use from 23 to 41 tons of farmyard manure: similarly one ton of sulphate of ammonia contains as much nitrogen as 30 to 50 tons farmyard manure. In the same way one ton of superphosphate of lime contains as much phosphoric acid as 28 to 64 tons farmyard manure.

The value of rotten manure is, weight for weight, greater than that of fresh manure. This is due to the fact that, while the water increases in amount, the loss of organic matter of a non-nitrogenous nature more than counterbalances the increase in water. The manure, therefore, becomes more concentrated in quality. The loss on the total weight, according to Wolff, in the rotting of farmyard manure, should not exceed in two or three months' time 16 to 20 per cent—viz., a sixth to a fifth of its entire weight. Not only, however, does the manure become richer in manurial ingredients, but the forms in which the manurial ingredients are present in rotten manure are more valuable, as they are more soluble. These statements must not be taken as proving that it is more economical to apply farmyard manure in a rotten condition than in a fresh one. The distinction must not be lost sight of which exists between relative increase—increase in the percentage of valuable constituents—and absolute increase. The increase in the value of the manure by the changes of the manurial ingredients from the insoluble to the soluble condition may be effected at the expense of a considerable amount of absolute loss of these valuable ingredients. This is a point which is probably too often left out of account in discussing the relative merits of fresh and rotten farmyard manure; and it is important that it should be clearly understood. In the words of the late Dr Voelcker: "Direct experiments have shown that 100 cwt. of fresh farmyard manure are reduced to 80 cwt. if allowed to lie till the straw is half rotten; 100 cwt. of fresh farmyard manure are reduced to 60 cwt. if allowed to ferment till it becomes 'fat or cheesy'; 100 cwt. of fresh farmyard manure are reduced to 40-50 cwt. if completely decomposed. This loss not only affects the water and other less valuable constituents of farmyard manure, but also its most fertilising ingredients. Chemical analysis has shown that 100 cwt. of common farmyard manure contain about 40 lb. of nitrogen, and that during fermentation in the first period 5 lb. of nitrogen are dissipated in the form of volatile ammonia; in the second, 10 lb.; in the third, 20 lb. Completely decomposed common manure has thus lost about one-half of its most valuable constituent."[167] While, of course, a very great amount of absolute loss of the valuable constituents—the nitrogen and ash-constituents—of farmyard manure may take place through volatilisation and drainage, by taking requisite precautions this loss may be very much minimised. As regards the total loss, this, in two or three months' time, should only amount to 16 to 20 per cent—or one-sixth to one-fifth of the weight.[168] The use of fixers, to which reference has already been made, will greatly minimise this loss. The application of fixers is best made to the manure when still in the stall or byre. The health of the animal benefits by so doing, while the manure is at once guarded against loss from this source.

As to the relative merits of covered and uncovered manure-heaps, much difference of opinion exists. It is one of those questions which does not admit of final decision one way or another, as it depends so largely on the individual circumstances of each case. That manure produced under cover is more valuable than manure made in the open is readily granted. The question, however, is as to whether the increase in its value is sufficiently great to warrant the extra expense involved in building covered courts. This depends on the individual circumstances of each case, and cannot be decided in a general way. For experiments on the relative value of manure made under cover and in the open, see Appendix.[169]

The method of applying farmyard manure to the field is a question which belongs more to the practical farmer than, to the scientist, and must be largely decided by economic considerations. There is an aspect, however, of the question which may well be treated here. The first point in the production of good manure is in connection with its even distribution. It is of great importance that the excrements of the different farm animals be thoroughly mixed together. By the intimate incorporation of the "hot" horse-dung with the "cold" cow and pig dung, uniform fermentation is secured. Fire-fang—or too rapid fermentation—may occur from this not being properly done, and from the manure becoming too dry. It is important, also, as we shall see immediately, to have the manure uniform in quality when applied to the field. The manure ought to be firmly trodden down, to moderate the rate of fermentation. Where the manure-heap is exposed to rain, the quantity of water it will naturally receive will probably be quite sufficient, if indeed not too much, to ensure a proper rate of fermentation—except, perhaps, in very warm weather. The great point to be aimed at is to ensure regular fermentation. What has to be especially avoided is any sudden exposure of the manure to large quantities of water. The result of such a washing-out of the soluble nitrogen is to retard fermentation, besides incurring the risk of great actual loss by drainage.[170]

Application of Farmyard Manure to the Field.

In applying the manure to the field, and before ploughing it in, two methods of procedure may be pursued. First, the manure may be set out in heaps, larger or smaller, over the field, and be allowed to remain in these heaps some time before being spread; and secondly, it may be directly spread broadcast over the field, and thus allowed to lie for some time. Lastly, the manure may be ploughed in immediately; and it may be stated that such a method is, where circumstances permit, the safest and most economical method.[171]

In discussing the merits and demerits of these two methods, Dr Heiden points out, first, with regard to the distribution of the manure in small heaps over the field, that this is not to be recommended, on the following grounds:—

1. Because the chances of loss by volatilisation are thereby increased. The manure is distributed several times instead of only once or twice.

2. It is apt to ensure unequal distribution. The separate heaps run the risk of losing their soluble nitrogenous matter, which soaks into the ground beneath the heaps. The other portions of the field not covered by the manure-heaps are thus manured with washed-out farmyard manure, bereft of its most valuable constituents. The result is, that while certain portions of the field are too strongly manured, other portions are too weakly manured.

3. The proper fermentation of the manure is apt to be interfered with by the loss of that which is its most important agent—viz., the soluble nitrogenous matter—and also by the drying action of the wind.

The same objections hold good to a large extent with regard to the setting out in the fields of the manure in large heaps. The risks of loss, in one respect, may be said to be less, owing to the smaller surface presented. On the other hand, they may be greater, owing to fermentation taking place more quickly. Agricultural practice, however, often renders this custom necessary; and if precautions are taken not to let the heap lie too long, and to cover it over with earth, the risk of serious loss may be rendered inconsiderable.

With regard to the second method of procedure—viz., the spreading of the manure broadcast over the field, and allowing it thus to lie—Dr Heiden is of opinion that this should only be done when the field is level. In the case of uneven ground the risks are, of course, obvious. It has been affirmed that, by allowing farmyard manure thus to lie exposed for some time, an important loss of volatile ammonia—carbonate of ammonia—is apt to take place. This could only take place where the former treatment of the farmyard manure had been bad. Hellriegel has shown that in the case of properly prepared farmyard manure there is no danger of loss in this way. The absorptive power of the soil for ammonia, it must be remembered, is very great, and the amount of volatile ammonia in farmyard manure is relatively so small that it is scarcely possible that any could escape in this way. Hellriegel's experiments have demonstrated this in a very striking way. He has found that in the case of a chalky soil, and during the summer and autumn months, practically no loss of ammonia takes place. The following considerations may be further urged in support of this method of application, as against immediately ploughing in the manure, viz.:—

1. That fermentation takes place more quickly.

2. That it results in a more equable distribution of the manurial constituents in the dung, by gradually and thoroughly incorporating the liquid portion of the manure with the soil-particles.

Against, however, these undoubted advantages, one serious disadvantage may be urged—viz., that the manure, before being ploughed in, becomes robbed to a large extent of its soluble nitrogenous compounds, which, as we have repeatedly observed, are so necessary for fermentation; and that, therefore, when it is ploughed in, it does not so readily ferment. This being so, it is highly advisable, in the case of light or sandy soils, not to follow such a practice, but to plough the manure directly in.

As to the depth to which it is advisable to plough the manure in, it may be here noticed that it should not be too deep, so as to permit of the access of sufficient moisture to ensure proper fermentation, and to prevent rapid washing down of nitrates to the drains. Lastly, it need scarcely be pointed out that it is highly important to have the manure evenly and thoroughly incorporated with the soil-particles. Where the manure is permitted to cake together in lumps, it may successfully resist the action of fermentation for several years.

Value and Function of Farmyard Manure.

Practical experience has long demonstrated the fact that farmyard manure is, taking it all round, the most valuable, and admits of the most universal application, of all manures; and science has done much to explain the reason of this. The influence of farmyard manure is so many-sided that it is difficult even to enumerate its different functions. As has already been pointed out, its indirect value as a manure is probably as great as, if indeed even not greater than, its direct value. In concluding our study of farmyard manure, we shall endeavour to summarise, in as brief a manner as possible, its chief properties.

First, as to its value as a supplier of the necessary elements of plant-food. This, there can be little doubt, has been, and still is, grossly exaggerated by the ordinary farmer. Much has been claimed for it as a "general" manure. How far it merits pre-eminence on this score among other manures will be seen in the sequel. It is true that, since it is composed of vegetable matter, it contains all the necessary plant ingredients.[172] As has been shown in the Introduction, there is practically in the case of most soils no necessity to add to a manure any more than the three ingredients, nitrogen, phosphoric acid, and potash. Its value, then, as a direct manure, must depend on the quantity and proportion in which these three ingredients are present. These substances, as we have already seen, it contains only in very small quantities. It is, judged from this point of view, a comparatively poor manure. Furthermore, only a certain percentage of these substances is in a soluble or immediately available condition,—in this respect the rotten manure being very much more valuable than the fresh manure.

Again, a point of great importance in a universal manure is the proportion in which the necessary plant-foods are present. If it be asked, Are the nitrogen, phosphoric acid, and potash in farmyard manure present in the proportion in which crops require these constituents? the answer must be in the negative. Heiden[173] has very strikingly illustrated this point, in so far as the relations between the two ash ingredients are concerned, by some computations as to the amount which would be removed from the soil in the course of different rotations.[174] In the case of five different rotations it was found that the ratio between the potash and phosphoric acid removed was as follows:[175] (1) 2.96 to 1; (2) 2.76 to 1; (3) 2.95 to 1; (4) 4.13 to 1; (5) 3.78 to 1. This would give a mean of 3.32 to 1. This is not the ratio in which these ingredients are generally present in farmyard manure. Farmyard manure may be said to be much richer in the mineral constituents of plants than in nitrogen. Professor Heiden found that in the case of a farm at Waldau, the crops in the course of ten years removed from a morgen (.631 of an acre) the following quantities:—

lb. Nitrogen 329 Potash 263 Phosphoric acid 121

In order to supply these amounts the following quantities of manure would require to be supplied:—

1. For the nitrogen, 26 or 27 tons (manure containing .606 per cent nitrogen).

2. For the potash, 20 to 25 tons (manure containing .672 per cent potash).

3. For the phosphoric acid, 13 to 19 tons (manure containing .315 per cent phosphoric acid).

From the above it will be seen that farmyard manure contains too little nitrogen in proportion to its ash ingredients.

It is not merely the amount of fertilising ingredients removed by the crop we have to take into account in estimating the value of certain manurial ingredients for the different crops. Two other considerations have to be remembered—viz., the amount of the constituents already present in the soil, and the ability of the different crops to obtain the ingredients from the soil. If we take into account these two considerations in estimating the value of farmyard manure as a general manure, we shall find that they accentuate the inadequacy of the ratio existing between the nitrogen and the mineral ingredients. Messrs Lawes and Gilbert have found in the Rothamsted experiments with farmyard manure, that while it restored the mineral ingredients, it was inadequate as a sufficient source of nitrogen. Nitrogen is, of all manurial ingredients, in least abundance in soils. It is consequently found that the ingredient in which farmyard manure requires to be reinforced is nitrogen. With regard to phosphoric acid and potash, it has already been shown that the ratio between them is probably greater than that in a good average manure. We should, arguing from this alone, be inclined to think that farmyard manure would be best reinforced with potash. The reverse is the case, however, as every farmer knows. This is due, first, to the fact that the potash, unlike the phosphoric acid, is entirely of a soluble nature, and therefore immediately available for the plant's needs; and secondly, to the fact that the necessity for the application of potash as a manure is generally not nearly so great as in the case of phosphoric acid. The result is, that farmyard manure will be, as a rule, more valuably supplemented by phosphoric acid than by potash.

Another point of great importance, in estimating the value of farmyard manure as a chemical manure, is the inferior value possessed by much of the nitrogen it contains, as compared with the nitrogen in such artificial manures as nitrate of soda and sulphate of ammonia. According to the Rothamsted experiments, weight for weight, the nitrogen in farmyard manure is not half so valuable as it is in sulphate of ammonia. Much of the nitrogen becomes only very slowly available; not a little of it perhaps actually takes years to be converted into nitrates.[176]

Thus, with regard to the direct value of farmyard manure as a manure, we have seen—

1. That it contains a very small quantity of the three fertilising ingredients.

2. That the proportion in which these three ingredients are present is not the best proportion for the requirements of crops.

3. That the form in which a portion of these ingredients—nitrogen and phosphoric acid—is present is not of the most valuable kind.

It is consequently not as a direct chemical manure that farmyard manure is pre-eminently valuable. We must seek for perhaps its most valuable properties in its indirect influence.

It adds to the soil a large quantity of organic matter. Most soils are improved by the addition of humus. The water-absorbing and retaining powers of a soil are increased by this addition of humus, while it enables the soil to attract an increased amount of moisture from the air. This is often of great importance, as in the period of germination of seed.[177] The influence it exerts on the texture of the soil in the process of fermentation is also very great. This is especially so in soils whose texture is too close, such as heavy clayey soils. It opens up their pores to the air, and renders them more friable. Where such an influence is most required, as in clayey soils, the manure ought to be applied in a fresh condition, so that the maximum influence exerted by the manure in this direction may be experienced. On light soils, on the contrary, whose friability and openness are already too great, and which do not require to be increased, the manure will be best applied in a rotten condition. It adds, further, greatly to the heat of the soils by its decomposition. Thus on cold damp soils it effects one very marked benefit. The influence it exerts in its decomposition upon the fertilising ingredients present in the soil is also by no means inconsiderable. In the process of its fermentation large quantities of carbonic acid gas are generated. This carbonic acid probably acts in a double capacity. It will, in the first place, greatly increase the solvent power of the soil-water, and thus enable it to set free an increased amount of mineral plant-food; and secondly, it will help to conserve a certain quantity of the soil-nitrogen, by preventing its conversion into nitrates.

As its indirect and mechanical properties are greatest when in its fresh condition, it will be better to apply it in that condition to soils most lacking in these mechanical properties. We may therefore say that farmyard manure is best applied in a rotted condition to light sandy soils, and to soils in a high state of cultivation, where its mechanical properties are not so much required.

An important point still remains to be discussed—viz., the rate at which the farmyard manure should be applied. This, of course, should naturally depend on a variety of circumstances—the amount of artificial manures used as supplementary to the farmyard manure, the frequency of its application, and the nature of the soil.

These considerations naturally vary so much, that the quantities of farmyard manure it is advisable to apply in different cases are widely different. There is a strong probability that the rate at which farmyard manure has been applied in the past has been grossly in excess of what could be profitably employed. Opinion is gaining ground among practical farmers, that smaller and more frequent applications of farmyard manure to the soil would be fraught with better results than the older custom of applying a large dressing at a time. This is an opinion in the support of which science can urge strong arguments. It is only of late years that we have come to recognise sufficiently the various risks which all fertilisers are subject to in the soil, and the importance, therefore, of minimising these risks as much as possible by putting into the soil at one time only as much manure as it is safely able to retain.

"The famous old German writer Thaer regarded 17 or 18 tons as an abundant dressing; 14 tons he called good, and 8 or 9 tons light. Other German authorities speak of 7 to 10 tons as light, 12 to 18 tons as usual, 20 or more tons as heavy, and 30 tons as a very heavy application."[178]

In the new edition of Stephens' 'Book of the Farm,'[179] from 8 to 12 tons per acre for roots, and from 15 to 20 tons for potatoes, along with artificials, which may cost from 25s. to 60s. per acre additional, are quoted as general dressings.

The majority of recent experiments with farmyard manure would seem to indicate that, even in the case of what are considered small dressings, the extra return in crop the first year after application is not such as to cover the expense of the manure. Of course, as is commonly pointed out, the effect of farmyard manure is of a lasting nature, and is probably felt throughout the whole rotation, or even longer. This, to a certain extent, is no doubt true; still it may be strongly doubted whether farmyard manure is, after all, an economical manure, as compared with artificial manures. The desirability of manuring the soil and not the crop is, in this age of keen competition, no longer believed in; and the Rothamsted experiments have shown that it is highly doubtful whether even the soil benefits to anything like a commensurate extent by the application of large quantities of farmyard manure. This is of course assuming for farmyard manure the value that it would fetch when sold, or, to put it rather differently, the price it would cost if the farmer had to purchase it. Farmyard manure is a necessary bye-product of the farm, and can scarcely be regarded, therefore, in the same light as the artificial manures which the farmer buys.[180]

FOOTNOTES:

[131] See Appendix, Note I., p. 279.

[132] "The large amount of potash in unwashed wool is very remarkable: a fleece must sometimes contain more potash than the whole body of the shorn sheep."—Warington's 'Chemistry of the Farm,' p. 78.

[133] See Appendix, Note II., p. 279.

[134] The urine of the pig, from the nature of its food, is, as a general rule, a very poor nitrogenous manure.

[135] See Appendix, Note XV., p. 290.

[136] See Appendix, Note III., p. 280.

[137] See Appendix, Note XVIII., p. 291.

[138] The nitrogen present in the urine, it may be well to point out, is derived from the waste of nitrogenous tissue as well as from nitrogenous matter of the food digested.

[139] Note IV., p. 281.

[140] Warington puts this matter admirably in the following words: "If the food is nitrogenous and easily digested, the nitrogen in the urine will greatly preponderate. If, on the other hand, the food is one imperfectly digested, the nitrogen in the solid excrement may form the larger quantity. When poor hay is given to horses, the nitrogen in the solid excrement will exceed that contained in the urine. On the other hand, corn, cake, and roots yield a large excess of nitrogen in the urine." ('Chemistry of the Farm,' p. 137).

[141] See p. 281.

[142] See p. 282.

[143] See Heiden's 'Duengerlehre,' vol. ii. p. 58.

[144] Heiden's 'Duengerlehre,' vol. i. p. 404.

[145] The following quantities of nitrogen are found in rye, pea, and bean straw:—

Ranging from Average Lb. per cent. per cent. per ton.

Rye-straw .30 to .73 .57 12.76 Pea-straw .76 to 1.61 1.21 27.10 Bean-straw 1.15 to 2.62 1.92 43.00

[146] Dr J. M. H. Munro recommends the sprinkling of a little finely sifted peat-powder in addition to straw, as an excellent means of preventing loss of volatile ammonia in the fermentation of manure.

[147] See 'Mark Lane Express,' October 7, 1889, p. 475.

[148] See Appendix, Note VII., p. 283.

[149] For analyses see Appendix, Note VIII., p. 283.

[150] According to Storer, in a ton of autumn leaves of the best quality there would be 6 lb. of potash, less than 3 lb. of phosphoric acid, and 10 or 15 lb. of nitrogen. Another substance that may be used as a litter is sawdust. This substance is a good absorbent, but is of little value as a manurial substance.

[151] Heiden's 'Duengerlehre,' vol. ii. pp. 34, 66. In Boussingault's experiments the food consisted of 15 lb. hay, 4.54 lb. oats, and 32 lb. water; the total excrements amounting to 31.16 lb., containing 7.42 lb. dry matter. In Hofmeister's experiments the food consisted of 5.23 lb. hay, 6.18 lb. oats, 1 lb. chopped straw, and 25.57 lb. water; the excrements amounting to 25.07 lb., containing 5.32 lb. dry matter.

[152] This is taking no account of the amount of water which the manure will absorb, and which will probably double the quantity.

[153] See Appendix, Note IX., p. 283.

[154] The rapid fermentation of horse-manure is due to its mechanical as well as its chemical nature. The horse does not reduce its food to such small pieces, and its urine is rich in nitrogen.

[155] Schulze recommends one-third of a pound per day of sulphate of lime for each horse.

[156] See Appendix, Note X., p. 284.

[157] The food consisted of 30 lb. potatoes, 15 lb. hay, and 120 lb. water.

[158] For further analyses of cow-manure, see Appendix, Note XI., p. 286.

[159] This is for a pig of six to eight months old, and fed on potatoes.

[160] It has been asserted that the use of pig-manure, when applied alone, is apt to give an unpleasant taste to the produce grown.

[161] Taken from a very large number of analyses by a number of experimenters. See Heiden's 'Duengerlehre,' vol. i. p. 99.

[162] See Storer, 'Agricultural Chemistry,' vol. ii. p. 96.

A question of great importance is as to the amount of farmyard manure produced on a farm in a year, and its value. This is a question which is extremely difficult to satisfactorily deal with. Various methods of calculating this amount have been resorted to. It may be well to state these pretty fully. Some practical authorities estimate the amount by calculating that every ton of straw should produce 4 tons of manure. Another method consists in estimating the amount from the size of the farm. Sir John Lawes has calculated the composition of farmyard manure which should be produced in the case of a farm of 400 acres, farmed on the four-course system. He assumes that half of the roots and 100 tons of hay are consumed at the homestead; that the whole of the straw of the corn crops is retained at home as food and litter; that twelve horses have corn equal to 10 lb. of oats per head per day; and that about ten shillings per acre are expended in the purchase of cake for feeding stock. Under these conditions the amount of farmyard manure should be 855 tons (or an average of 8-1/2 tons for each of the 100 acres of root-crop) of fresh undecomposed dung. (For composition, see Appendix, Note XVII., p. 291.) Another method is by taking, as the data of calculation, the number of cattle, horses, sheep, &c., producing the manure. Lloyd considers that a fattening animal requires 3 tons of straw in the year, and makes about 12 tons of manure. A farmer, therefore, should make 8 tons of manure for every acre of that part of his land which, in the four-course rotation, is put down to turnips.

The last method consists in taking as the data the amount of food consumed and litter used in the production of the manure. Of these methods Heiden considers the last as alone satisfactory and trustworthy. Applying this method to the horse, he shows, from experiments, that a little over 47 per cent of the dry matter of its food has been proved to be voided in the solid and liquid excreta. Taking the average percentage of water in the excreta as about 77.5, the percentage of dry matter in the excreta will be 22.5. That is, every pound of dry matter in the food eaten by the horse yields a little over 2 lb. of excrementitious matter. To this of course must be added the amount of straw used as litter, which may be taken at 6.5 lb.

From these data we may calculate the amount of manure produced in a year by a horse, making certain assumptions as to the amount of work performed. This Heiden does by assuming that a horse works 260 days, of twelve hours each, in the course of a year, or 130 whole days, spending 235 days in the stall. Calculating from the above data, he estimates that a well-fed working horse will produce about 50 lb. of manure in a day, or 6.5 tons in a year. Of course this does not necessarily represent all the manure actually produced by the horse, but how much of the remaining portion of the manure actually finds its way to the farm it is impossible to say. According to the 'Book of the Farm,' Division III. p. 98, a farm-horse makes about 12 tons of manure in a year.

It has been calculated that cows void about 48 per cent of the dry matter of their food in the solid and liquid excreta, which contain of water, on an average, 87.5 per cent. That is, every pound of dry matter will furnish 3.84 lb. of total excreta. By adding the necessary amount of straw for litter (which may be taken at one-third the weight of the dry matter of the fodder), Heiden calculates that an ox weighing 1000 lb. should produce 113 lb. of manure in a day, or 20 tons in a year. The 'Book of the Farm,' Division III. p. 98, gives the annual amount at from 10 to 14 tons. According to Wolff, one may assume that on an average the fresh excrements (both liquid and solid) of the common farm animals (with the exception of the pig) contain of every 100 lb. of dry matter in the food consumed about 50 lb., or a half. Estimating the dry matter in the litter used at equal to about 1/4 of the dry matter of the food, this would mean that for every 100 lb. of dry matter consumed in food there would be 75 lb. of dry manure (viz., 50 lb. dry excrements + 25 lb. dry litter), which would yield 300 lb. of farmyard manure in the wet state—i.e., with 75 per cent water. The amount of food daily required per every 1000 lb. of live-weight of the common farm animals may be taken, roughly speaking, at 24 lb. dry food material and 6 lb. of straw as litter. The daily production of manure for 1000 lb. of live-weight would amount, therefore, to 18 lb. of dry, or 72 lb. wet manure. (See Appendix, Note XVII., p. 291.) According to J. C. Morton and Evershed, oxen feeding in boxes require 20 lb. of straw per head per day as litter. An ox, therefore, will make 8 tons of fresh dung in six months, using 32 cwt. of litter. This means that each ton of litter gives 5 tons of fresh dung. It is calculated that nearly twice as much litter must be used in open yards.

[163] It has been calculated that under ordinary circumstances sheep-dung, when allowed to ferment by itself, should do so in about four months, horse-dung in six months, and cow-dung in eight months.

[164] See Appendix, Note XII., p. 286.

[165] See Heiden's 'Duengerlehre,' vol. ii. p. 156.

[166] Warington, 'Chemistry of the Farm,' p. 33.

[167] Recent experiments by Muentz and Girard in France have shown that the loss in sheep excreta from volatilisation of the carbonate of ammonia amounted to over 50 per cent. By the use of straw litter this was reduced to about a half less, and with earth litter one quarter less.

[168] See Appendix, Note XIII., p. 288.

[169] See Appendix, Note XIV., p. 289.

[170] See Appendix, Note XV., p. 290.

[171] For spring application rotten farmyard manure is generally used, because in this condition its fertilising matter is more quickly available. On light land it is best to apply it in the rotten condition shortly before it is likely to be used. (See p. 261.)

[172] The total amount of plant-food in a ton of farmyard manure is together less than 1/20th of its total weight.

[173] See Heiden's 'Duengerlehre,' vol. ii. p. 171.

[174] For full details see Appendix, Note XVI., p. 290.

[175] Storer reproduces these results in his 'Agricultural Chemistry,' vol. ii. p. 21.

[176] This aspect of farmyard manure has been ably stated by Mr F. J. Cooke, a well-known Norfolk farmer. In commenting on the results of the Rothamsted experiments, he says: "It is clear enough that the faith of the farmer in the soil-enriching character of his home-made manure is amply justified; the only question being, indeed, if this quality be not too highly appreciated. It is not, after all, so much by the fattening of our land as by the bounty of the crop grown upon it that we reap the fruit of our exertions. The man of scientific mind keeps his purpose fixed on the production of good crops mainly, and the cheapest way to grow them. The experiments under consideration show that richness of land may be purchased much too dearly, and that richness of crop by no means bears the necessary relation to richness of soil which has sometimes been imagined. We may boast of the 'lasting qualities' of our dung, but the answer of science by these experiments is, that so great is the last that the life of one man may not be long enough to exhaust it. In the extravagant use of dung, therefore, such considerations, amongst many others, as length of purse, as well as length and character of tenure, must clearly be taken into account."

[177] See paper on "Manurial Experiments with Turnips" by author, in 'Transactions of the Highland and Agricultural Society of Scotland;' 1891.

[178] Storer's 'Agricultural Chemistry,' vol. i. p. 498.

[179] Division III. p. 130.

[180] Mr F. J. Cooke, who has already been quoted, has kindly furnished the author with his views on the peculiar functions of farmyard manure as a manure. He says: "I look upon it, broadly speaking, as chiefly of value in restoring to good land, after cropping, those particular advantages which good land alone can give, and in helping better than any other manure, when applied to poor land, to bring it up to the level of good land in those particular merits which belong alone to fine soils. I speak now of an inherent value in good soils, beyond that attaching to them as mere reservoirs of abundant plant-food. For instance, one may supply a poor soil by artificial manure with much more food—and in a highly soluble condition—than is needed by the crop to be grown upon it, and yet not get so good a crop as upon a naturally richer but otherwise similar soil less abundantly filled with immediately available food. This may arise from a more perfect distribution of the plant-food in the rich soil, or from the steady way in which it becomes available to the crop, as well as for other reasons. But whatever the cause, there, I think, is the broad fact of the power of farmyard manure to enrich poor soils, so to speak, more naturally—that is, in a way which makes them more nearly correspond to better soils than artificial manures can."

Hence the indirect benefit to the farmer from farmyard manure is probably greater than its direct value as a mere manure. And the usual provision and use of it amongst all straw-growing farmers is sufficiently justified. The extent, however, to which that course may be beneficially carried, is one of the most important of the many difficult economic and scientific problems which the farmer has to face.

On the economic side must of course be considered the cost of manufacture in individual instances, as ruled by the market value of the straw, and the different circumstances and conditions under which the various farm animals are kept and fed (I have the figures by me of one well-known farmer, which show the cost to him of every ton of home-made manure to be 20s. or more); the price the resultant crops may be expected to command; the cost at the moment of artificial manures, &c., &c. Whilst on the scientific side must be considered the nature of the soil, the particular rotation of crops, &c.

It was, amongst others, just these scientific and yet very definite and practical problems we have tried to throw light on in the series of field experiments conducted for several years by the Norfolk Chamber of Agriculture. (See reprint of summary of same in last year's Report of the Board of Agriculture.)



APPENDIX TO CHAPTER VII.

NOTE I. (p. 225).

DIFFERENCE IN AMOUNT OF EXCRETA VOIDED FOR FOOD CONSUMED.

With regard to the difference in the composition of the solid excreta voided by different fattening animals fed on the same amount of food, see Warington's 'Chemistry of the Farm,' p. 125, where it is shown that for equal amount of live-weight, the sheep produces on the same weight of dry food very much more manure than the pig, while the ox produces even more than the sheep. Of course this does not refer to the total amount of manure produced by the different animals, but only to the amount of manure produced from the consumption of equal quantities of food. This would seem to be owing to the greater capacity the pig has for assimilating its food.

NOTE II. (p. 227).

SOLID EXCRETA VOIDED BY SHEEP, OXEN, AND COWS.

To contrast with the analyses given by Stoeckhardt, it may be well to cite those based on Lawes and Gilbert's experiments, and quoted by Warington ('Chemistry of the Farm,' p. 138):—

I.—SHEEP (fed on meadow-hay).

SOLID EXCREMENT. Fresh. Dry. Water 66.2 - Organic matter 30.3 89.6 Ash 3.5 10.4 —— —— Nitrogen .7 2.0

II.—OXEN (fed on clover-hay and oat-straw, with 8 lb. beans per day).

Fresh. Dry. Water 86.3 - Organic matter 12.3 89.7 Ash 1.4 10.3 —— —— Nitrogen .3 1.9

III.—COWS (fed on mangels and lucerne hay).

Mangels. Lucerne hay. Water 83.00 79.70 Nitrogen .33 .34 Phosphoric acid .24 .16 Potash .14 .23

NOTE III. (p. 232).

URINE VOIDED BY SHEEP, OXEN, AND COWS.

The following are the results for urine, the animals being fed as in Note II.:—

Sheep. Oxen. Fresh. Dry. Fresh. Dry. Water 85.7 - 94.1 - Organic matter 8.7 61.0 3.7 63.0 Ash 5.6 39.0 2.2 37.0 —— —— —— —— Nitrogen 1.4 9.6 1.2 20.6

Cows. Mangels. Lucerne hay. Water 95.94 88.25 Nitrogen .12 1.54 Phosphoric acid .01 .006 Potash .59 1.69

NOTE IV. (p. 233).

PERCENTAGE OF FOOD VOIDED IN THE SOLID AND LIQUID EXCREMENTS.

According to Wolff, the following table shows the percentage of the dry substance of the food which is voided in the solid and liquid excrements of the cow, ox, sheep, and horse:—

Cow. Ox. Sheep. Horse. Average. Solid excreta 38.0 44.0 42.6 46.7 42.8 Urine 5.8 6.3 6.8 5.7 6.2 —— —— —— —— —— Total 43.8 50.3 49.4 52.4 49.0

NOTE V. (p. 234).

PIG EXCREMENTS.

The excrements voided by pigs are poor in manurial constituents, because the food on which they are fed is generally of a very poor nature. In their case the urine is always very much richer in manurial ingredients than the solid excreta. The relative composition of the solid excreta and the urine will be best illustrated by quoting some experiments carried out by Wolff on this subject. The experiments were carried out with two pigs nine and a half months old, and each 121.9 kilogrammes (a kilogramme is equal to about 2-1/4 lb.) in weight. The first consumed daily 1000 grammes of barley, 5000 grammes of potatoes, and 2572 grammes of sour-milk. The second one consumed the same quantities of potatoes and sour-milk as the first, and 1000 grammes of peas. The following table gives the results of excreta and urine daily voided, in grammes:—

Dry Nitrogen. Ash. Potash. Lime. Magnesia. Phosphoric substance acid. Solid { I. 217.7 8.7 28.6 7.3 4.4 3.0 10.3 excreta { II. 161.1 9.1 31.1 5.9 4.9 2.8 11.1

Urine { I. 112.8 19.3 56.2 33.0 0.4 0.9 6.7 { II. 137.7 30.6 62.2 37.1 0.2 1.1 7.1

NOTE VI.(p. 236).

MANURIAL CONSTITUENTS IN 1000 PARTS OF ORDINARY FOODS.

Based on Lawes and Gilbert's Analyses.

(Warington's 'Chemistry of the Farm,' p. 139.)

- - - - Dry Nitrogen. Potash. Phosphoric matter. acid. - - - - Cotton-cake, decorticated 918 70.4 15.8 30.5 Rape-cake 887 50.5 13.0 20.0 Linseed-cake 883 43.2 12.5 16.2 Cotton-cake, undecorticated 878 33.3 20.0 22.7 Linseed 882 32.8 10.0 13.5 Palm-kernel meal, English 930 25.0 5.5 12.2 Beans 855 40.8 12.9 12.1 Peas 857 35.8 10.1 8.4 Malt-dust 905 37.9 20.8 18.2 Bran 860 23.2 15.3 26.9 Oats 870 20.6 4.8 6.8 Rice-meal 900 19.1 6.1 23.8 Wheat 877 18.7 5.2 7.9 Rye 857 17.6 5.8 8.5 Barley 860 17.0 4.7 7.8 Maize 890 16.6 3.7 5.7 Brewers' grains 234 7.8 0.4 3.9 Clover-hay 840 19.7 18.6 5.6 Meadow-hay 857 15.5 16.0 4.3 Bean-straw 840 13.0 19.4 2.9 Oat-straw 857 6.4 16.3 2.8 Barley-straw 857 5.6 10.7 1.9 Wheat-straw 857 4.8 6.3 2.2 Potatoes 250 3.4 5.8 1.6 Swedes 107 2.2 2.0 0.6 Carrots 140 2.1 3.0 1.1 Mangels 120 1.8 4.6 0.7 Turnips 80 1.6 2.9 0.8 - - - -

NOTE VII. (p. 241).

ANALYSES OF STABLE-MANURE, MADE RESPECTIVELY WITH PEAT-MOSS LITTER AND WHEAT-STRAW (by BERNARD DYER, B.Sc.)

Peat-moss litter. Wheat-straw. Per cent. Per cent. Total nitrogen 0.88 0.61 Equal to ammonia 1.07 0.74 Phosphoric acid 0.37 0.43 Equal to Tribasic phosphate of lime (or Tricalcic phosphate) 0.80 0.94 Potash 1.02 0.59

NOTE VIII. (p. 242).

ANALYSES OF BRACKEN (by J. HUGHES, F.C.S.)

No. 1 No. 2 Young fern. Old fern. Per cent. Per cent.

Water 11.66 14.90 * Organic matter 83.38 80.54 + Mineral matter 4.96 4.56 ——— ——— 100.00 100.00 ——— ——— Containing— * Nitrogen 2.42 0.90 + Silica 1.60 2.81 Potash 1.15 0.10 Soda 0.64 0.26 Lime 0.44 0.62 Magnesia 0.13 0.47 Phosphoric acid 0.60 0.30

NOTE IX. (p. 244).

ANALYSES OF HORSE-MANURE.

For a fuller discussion of this question, the reader is referred to Heiden's 'Duengerlehre,' vol. ii. p. 185, and also to Storer's 'Agricultural Chemistry,' vol. i. p. 575. The statements in the different text-books as to the quantity of manure produced by the horse are such as naturally to perplex the student. This discrepancy is due, however, to the different methods adopted by different writers of calculating this amount. The subject is further discussed in the footnote to p. 252. The following analyses of horse-manure may be valuable for reference. They are taken from Storer's 'Agricultural Chemistry,' vol. i. p. 496:—

- - - - - - 1. 2. 3. 4. 5. Average. - - - - - - Water 75.76 69.30 67.23 72.13 71.30 71.15 Dry matter 24.24 24.82 32.72 27.87 28.70 27.67 Ash ingredients 5.07 5.05 6.49 3.37 3.30 4.65 Potash 0.51 0.63 0.22 0.59 0.53 0.49 Lime 0.30 0.74 0.17 0.41 0.21 0.36 Magnesia 0.19 0.29 0.20 0.17 0.14 0.20 Phosphoric acid 0.41 0.67 0.35 0.12 0.28 0.36 Ammonia 0.26 0.12 0.15 0.44 - 0.24 Total nitrogen 0.53 0.69 0.47 0.67 0.58 0.59 - - - - - -

NOTE X. (p. 247).

THE NATURE OF THE CHEMICAL REACTIONS OF AMMONIA "FIXERS."

For the student, the exact nature of the chemical reactions taking place may be of interest.

In the first place, it must be distinctly understood that the form in which ammonia escapes from the manure-heap is not, as is so commonly erroneously stated in agricultural text-books, as "free" ammonia. Whenever ammonia is brought into contact with carbonic acid, carbonate of ammonia is formed. When it is remembered that carbonic acid is by far the most abundant of the gaseous products of the decomposition of organic matter, it will be at once seen that free ammonia could not exist under such circumstances.

1. In the case of hydrochloric acid, the following chemical equation will represent the nature of the reaction—

2HCl + (NH{4}){2}CO{3} = 2NH{4}Cl + H{2}O+CO{2} (Hydrochloric (carbonate of ammonia,) (sal-ammoniac,) (carbonic acid.) acid,)

2. In the case of sulphuric acid, the equation will be—

H{2}SO{4} + (NH{4}){2}CO{3} = (NH{4}){2}SO{4} + H{2}O+CO{2} (Sulphuric (carbonate of (sulphate of ammonia,) (carbonic acid.) acid,) ammonia,)

3. With _gypsum_ (CaSO_{4})—

CaSO{4} + (NH{4}){2}CO{3} = CaCO{3} + (NH{4}){2}SO{4} (Gypsum,) (carbonate of (calcium (sulphate of ammonia.) ammonia,) carbonate,)

4. With _copperas_ (FeSO_{4})—

FeSO{4} + (NH{4}){2}CO{3} = FeCO{3} + (NH{4}){2}SO{4} (Sulphate of (carbonate of (ferrous (sulphate of ammonia.) iron,) ammonia,) carbonate,)

5. With _sulphate of magnesia_ (MgSO_{4})—

MgSO{4} + (NH{4}){2}CO{3} = MgCO{3} + (NH{4}){2}SO{4} (Sulphate of (carbonate of (carbonate of (sulphate of magnesia,) ammonia,) magnesia,) ammonia.)

Reference has been made to the fact that magnesium sulphate may probably not only fix the ammonia, but the phosphoric acid. When magnesium sulphate, soluble phosphoric acid, and ammonia are brought in contact with one another, the double insoluble phosphate of ammonium and magnesium (MgNH{4}PO{4}6Aq) is formed. While such a reaction is possible, it is highly improbable that it takes place to any extent. The double phosphate is a crystalline salt which only separates after a considerable time, and in the presence of a large excess of ammonia.

NOTE XI. (p. 250).

ANALYSES OF COW-MANURE.[181]

+ -+ -+ -+ -+ -+ -+ 1. 2. 3. 4. 5. 6. Average. + -+ -+ -+ -+ -+ -+ Water 85.30 77.71 74.02 72.87 75.00 77.50 77.06 Dry matter 14.70 22.30 25.98 27.13 25.00 22.50 22.93 Ash ingredients 2.04 4.71 3.94 6.70 6.22 2.20 4.30 Potash 0.36 0.46 0.56 1.69 0.39 0.40 0.64 Lime 0.29 0.37 0.58 0.41 0.24 0.31 0.48 Magnesia 0.19 0.11 0.13 - 0.18 0.11 - Phosphoric acid 0.16 0.13 0.07 0.20 0.14 0.16 0.14 Ammonia 0.06 0.16 0.07 - 0.27 - 0.14 Total nitrogen 0.38 0.54 0.41 0.79 0.46 0.34 0.48 + -+ -+ -+ -+ -+ -+

NOTE XII. (p. 259).

COMPOSITION OF FRESH AND ROTTEN FARMYARD MANURE (VOELCKER).

Composition of fresh manure, composed of horse, cow, and pig dung, about fourteen days old:—

Water 66.17 * Soluble organic matter 2.48 Soluble inorganic matter 1.54 + Insoluble organic matter 25.76 Insoluble inorganic matter 4.05 ——— 100.00 ——— * Containing nitrogen .149 Equal to ammonia .181 + Containing nitrogen .494 Equal to ammonia .599 Total percentage of nitrogen .643 Equal to ammonia .780 Ammonia in a volatile state .034 Ammonia in form of salts .088

Composition of the whole ash:—

Soluble in water, 27.55 per cent:— Soluble silica 4.25 Phosphate of lime 5.35 Lime 1.10 Magnesia 0.20 Potash 10.26 Soda 0.92 Chloride of sodium 0.54 Sulphuric acid 0.22 Carbonic acid and loss 4.71

Insoluble in water, 72.45 per cent:— Soluble silica 17.34 Insoluble silicious matter 10.04 Oxide of iron and alumina with phosphates 8.47 (Containing phosphoric acid, 3.18 per cent.) (Equal to bone-earth, 6.88 per cent.) Lime 20.21 Magnesia 2.56 Potash 1.78 Soda 0.38 Sulphuric acid 1.27 Carbonic acid and loss 10.40 ——— 100.00 ———-

Composition of rotten dung, six months old, is as follows:—

Water 75.42 * Soluble organic matter 3.71 Soluble inorganic matter 1.47 + Insoluble organic matter 12.82 Insoluble inorganic matter 6.58 ——— 100.00 ———

* Containing nitrogen .297 Equal to ammonia .360 + Containing nitrogen .309 Equal to ammonia .375 Total amount of nitrogen .606 Equal to ammonia .735 Ammonia in a volatile state .046 Ammonia in form of salts .057 Composition of the whole ash:—

Soluble in water, 18.27 per cent:—

Soluble silica 3.16 Phosphate of lime 4.75 Lime 1.44 Magnesia 0.59 Potash 5.58 Soda 0.29 Chloride of sodium 0.46 Sulphuric acid 0.72 Carbonic acid and loss 1.28

Insoluble in water, 81.73 per cent:— Soluble silica 17.69 Insoluble silica 12.54 Phosphate of lime - Oxides of iron alumina with phosphates 11.76 (Containing phosphoric acid, 3.40 per cent.) (Equal to bone-earth, 7.36 per cent.) Lime 20.70 Magnesia 1.17 Potash 0.56 Soda 0.47 Chloride of sodium - Sulphuric acid 0.79 Carbonic acid and loss 16.05 ——— 100.00 ———

NOTE XIII. (p. 263).

COMPARISON OF FRESH AND ROTTEN MANURE (WOLFF).

Fresh. Moderately rotten (Taking the quantity of dry matter as the same.) Dry matter 25.00 25.00 Ash 3.81 4.76 Nitrogen 0.39 0.49 Potash 0.45 0.56 Lime 0.49 0.61 Magnesia 0.12 0.15 Phosphoric acid 0.18 0.23 Sulphuric acid 0.10 0.13 Silica 0.86 1.08

NOTE XIV. (p. 263).

LORD KINNAIRD'S EXPERIMENTS.[182]

"Lord Kinnaird has given the particulars of a very careful experiment. He tried to test the comparative value of manure kept in an open court with that kept under cover. He selected the same kind of cattle, gave them the same kind and quantity of food, and bedded them with the same kind of straw. A field of 20 acres of uniform land was selected. This having been equally divided, 2 acres out of each 10 gave the following results:—

Potatoes grown with Uncovered Manure.

Tons. cwt. lb. First measurement—1 acre produced. 7 6 8 Second do. do. do. 7 18 99

Potatoes grown with Covered Manure.

First measurement—1 acre produced. 11 17 56 Second do. do. do. 11 12 26

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.

Weight per Produce in grain. bushel. Produce in straw. Acre. bushels. lb. lb. stones. lb. First 41 19 61-1/2 152 of 22 Second 42 38 61-1/2 160 of 22

Wheat grown with Covered Manure.

First 53 5 61 220 of 22 Second 53 47 61 210 of 22"

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):—

Dry substance 18.0 Magnesia 0.4 Ash 10.7 Phosphoric acid 0.1 Nitrogen 1.5 Sulphuric acid 0.7 Potash 4.9 Silica 0.2 Lime 0.3

NOTE XVI. (p. 270).

AMOUNTS OF POTASH AND PHOSPHORIC ACID REMOVED BY THE FOLLOWING ROTATIONS FROM A PRUSSIAN MORGEN (.631 ACRE).

Potash. Phosphoric acid. lb. lb. 1. Wheat 16.40 10.67 Oats 10.47 4.59 Potatoes 66.41 18.33 Hay 39.54 11.32 ——— ——- 132.82 44.91 ——— ——- The ratio of potash to phosphoric acid is 2.96 to 1.

2. Wheat 16.90 10.67 Barley 17.44 10.65 Potatoes 66.41 18.33 Hay 39.54 11.32 ——— ——- 140.29 50.97 ——— ——- The ratio of potash to phosphoric acid is 2.76 to 1.

3. Rye 20.03 12.15 Oats 10.97 4.59 Potatoes 66.41 18.33 Hay 39.54 11.32 ——— ——- 136.95 46.39 ——— ——- The ratio of potash to phosphoric acid is 2.95 to 1.

4. Wheat 16.90 10.67 Oats 10.97 4.59 Mangels 148.54 25.62 Hay 39.54 11.32 ——— ——- 215.95 52.20 ——— ——- The ratio of potash to phosphoric acid is 4.13 to 1.

5. Rye 20.03 12.15 Barley 17.44 10.65 Mangels 148.54 25.62 Hay 39.54 11.32 ——— ——- 225.55 59.74 The ratio of potash to phosphoric acid is 3.78 to 1.

NOTE XVII. (pp. 253, 254).

COMPOSITION OF FARMYARD MANURE (FRESH), (calculated by SIR JOHN LAWES).

Phosphoric acid Total dry Total mineral calculated as Potash. Nitrogen. matter. matter. phosphate of lime. Percent 30.0 2.77 .50 .53 .64 Per ton (in lb.) 67.2 62.0 11.1 12.0 14.3

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:—

1 ton of urine contains 1 ton of solid excreta in lb.: contains in lb.:

Nitrogen. Potash. Nitrogen. Cow 30 20 9 Horse 36 22 12 Sheep 38 30 16

FOOTNOTES:

[181] Storer's 'Agricultural Chemistry,' vol. I. p. 496.

[182] Scott's 'Manures and Manuring,' p. 19.



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 debris, 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 deg. Fahr.):—

1. Constituents easily soluble in Water.

Urate of ammonium 12.74 Oxalate of ammonium 13.60 Nitrogenous and sulphurous organic substances 3.61 Ammonium-magnesium phosphate 4.00 Ammonium phosphate .90 Ammonium sulphate 1.82 Ammonium chloride 1.55 Potassium sulphate 3.30 Sodium chloride 2.44 ——- 43.96 ——-

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

Uric acid 21.14 Resin 1.11 Fatty acids 1.60 Nitrogenous and sulphurous organic substances 2.29 Calcium phosphate 18.22 Phosphate of iron 1.04 Silica .64 ——- 46.04 ——-

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, Phoenix, 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.

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.

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